Edeor

Elegyto0es

The positive impedance converter

14 -bit D -A converter

SSB adapter

1 1 1 11 11 1770268 451005

EE

October 1987

BBC Micro Computer SystemBBC MASTER SERIES:AMB15 BBC MASTER 128K £375 (a)AMB12 BBC MASTER Econet _ E315 (a)ADC06 Turbo (65C1021 Card £99 Id)ADC08 512 Processor £195 1b1

ADF14 Rom Cartridge . £12.75 (c)ADF10 Econet Card £41 id/ADJ22 Ref. Manual I £14 IclADJ23 Ref. Manual Part II E14 (c)ADJ24 Ref Manual . £18 ic)

BBC ARCHIMEDESPlease enquire about avaaabWty anddetails of the stern.

UPGRADE KITS:1.2 OS ROM £15 fobONES ROM £17.50 (dlBASIC II ROM (BBC B) . . £22.50 tillADES ROM E26 (di"770 DES Kit £43.50 (dlScoria Kit (B&B-) £55 (dl

ACORN ADD-ON PRODUCTS:Torth ZEP 100 E229 (a)512 2nd Processor £195 lb)IEEE Interface ....... E265 lb)Teletext Adapter (95 lb$

Ask for fun details on our full range of software

WORD PROCESSOR ROMs:VIEW 2.1 . £37 (di VIEW 3.0 E49Sp.e8master £49 (d) VIEW INDEX £12WORDW1SE £24 (d) WORDWISE- £38 idl

SPELLCHECK (!WYSRV1G+ E21 (dl £31 fdiINTERWORD £46 EDWORD II £43

LANGUAGE ROMS:Micro Prolog E62 lc) Microtext . E52ISO PASCAL £47 fcl LOGOTRON E56LOGO . £46 Icl MACRONS E33 io.LISP E39 loll COMAL £43 fdl

Oxford Pascal E36 (c)

COMMUNICATIONS ROMS:TERMULATOR £25 fdMASTER TERMULATOR (34.75 IdCOMMUNICATOR E49 (dCOMMSTAR £28 IdMODEM MASTER £34 IdCOMMAND E34 id

UTILITY ROMs:DOTPR(NT PLUS for FX.RX compatiblesDOTPRINT DUAL for MX rangeAcorn Graphics Extension Rom £28 (dlMvfen with 57 disc utility commands100 page manual £37.50 Icl

MULTIFORM Z80 2nd Processor for the BBCThis unique Z80 2nd Processor running OS,M win allow use of almost -dam! CP.1.1 soft-ware On the BBC micro. It is supplied with a number of &Relent CP 7.! f% and includes autility to configured to read other formats. This is particularly useful - - - here com-puters with different CRM formats are used and the data cannot to . _ betweenthem. Mains powered (includes Pocket Wordstar & MSDOS RAN tit : £249 Ib)MSZOS ReadWrite Utitiry £49 (CI

META Version 3 ASSEMBLERAssembles 17 of the popular processors. Over 70K long program on two rams and a &sr andprovides complete &Ind% and Assembly friaries_ It uses appropriate mnemonics for differentprocessors. Fully nestatie macros. nestable conditional assembly IIEELSEENDIR,source code. true local and global lahers. 32 bit labels and arithmetic. 30 ways to send ob:actcode and 50 directives_A powerful editor with many features. Send for detailed leaflet. E145

PRINTERSEPSON KP915 (156 col) E369 fa)LX800 E209 (Cl BROTHER HR20 (349 (alFX800 .. .. E329 fat STAR NL10 IPar.lel ITface).. £190 (alFX 1000 £449 fal STAR NL10 (Serial Interface' . £219 falEX800 £409 (a( JUKI 6100 (Daisy Wheel) .... £319 (a)LQ800 180 col) _ £439 (a) INTEGREX 1Colotal £549 falLQ1000 (136 cod £589 fa) NAT PANASONIC KX P 1081. E159 fa)TAXAN KP815 180 coil £269 (al NAT PANASONIC KX P 3131. £249 falWe hat/ in stock a large scariery of printer 3ttoCh7W#5. Interfaces and consurnables.Please svnie or phone for detss.

BBC DISC DRIVES5.25" Single Drive:1 x 400K 40,80T DS: TS400 ... £105 (Cl PS400 with psu £115 lb)5.25" Dual Drive:2 r 400K 40:80T OS: TD800 .... £185 fa) P1)800 with psu . £209 lel2 x 400K 40i8OT DS with psu and Wit in monitor stand PD800P £229 fal3.5" Drives:1 x 400K 80T DS TS35 1 E75 lb) PS35 I with psu £99 (Dl1 x 400K 80T DS with psi{ TD35 2 E135 ,L, P035 2 with psu E169 dal

ACCESSORIESBUFFALO 32K Buffer for Epson painters E75 FX80 plus sheet f £129 Ibl:EPSON Serial Interface: 8143 E30 10): 8148 with 2K buffer £65 101.

EPSON Paper Rall Holder £17 (b); FX80.50 - .85 Tractor Attach £37 lb): RX:FX80Dust Cover £4.50 (dl; LX80 Tractor Unit E20 fel; LC1800 Tractor Feed (47EPSON Ribbons: filkRX,FX80 £5: 1.4X,RX_FX100 £10 (dl: LX80 £4.50 (dl;

!UM: Serial Interface £65 (dl: Tractor Attach. £149 tall Sheet Feeder £219 fal:Ribbon £2.50 (al; Spare Daisy Wheel £14 (d).BROTHER HR20. Sheet Feed £229; Ribbons - Carbon or Nylon £3.: Tractor Feed(116 (al; 2000 Sheets Fanfold with extra fine prat 9.5" - £13.50: 15" £17.50 lb).BBC Parcel Lead £6: Serial Lead E6 (di: IBM Paralel Lead (2(n) (12.1111.

3M FLOPPY DISCSIndustry standard floppy discs with a life time guarantee. Discs in packs of 10:

5'i. DISCS 3h DISCS401 SS DD £8.50 Id) 401 DS DD £10.50 (d) 80T SS DD £15.00 id)80T SS DD£11.50 (dl 80T DS DD . £13.25 (dl 80T DS DD £19.50 (dl

DISC ACCESSORIESSingle D)sc Cable E6 (dl Dual Disc Cabe £8.50 (dl10 Disc Library Case E1.80 lc) 30 Disc Storage Box. £6 fcl40 Disc Lockable Box E8.50 Icl 100 Disc Lockable Box £13 IclRoeticlene DrWehead Ginning Kit with 20 Wig.. xtVri cleaning kits 51i" E14.50 (dl: 3.:" £16 (dl

MONITORSMICROVITEC 14" RGB TAXAN K12SV620 12" £279 (al1431 Standard Resolution £179 (al TAXAN K12SV625 12" £329 (al1451 Medium Resolution E225 (a) 12" MONOCHROME MONITORS:1441 Hi Res E365 (al TAXAN:MICROVITEC 14" RGBJPAL & Audio Taxan KX 117 12" Green P31 E B5 (a)1431 AP Standard Resolution E199 la) Taxan KX 118 12" Green P39 £ 95 (a)1451 AP Medium Resolution £259 (a) Taxan KX 119 12" Amber .. £ 95 fa)

PHILIPS:7502 Green Screen E 75 la)7522 Amber Screen E 79 (a)7542 `.*. een E 79 la)Ad Pr supplied with swivelstand

MICROVTIEC 20" RGB.PALfAusSo2030 CS std Res E380 fat2040 CS Hi Res £685 la)Mitsubishi 14" RGB Med Res. (BBC IBM(

E219

BT APPROVED MODEMSMIRACLE TECHNOLOGY WS Range

WS4000 V21123.Hayes Compatible. Intelligent. Auto DratAuto Answer) £140 101WS3000 V21/23 ProfessionalAs WS4000 and with BELL standards andbattery back up for memory E265113)WS3000 V22 ProfessionalAs WS3000 V21/23 but with 1200 baud fullduplex £445 falWS3000 V22 his ProfessionalAs V22 and 2400 baud full duplex £585 la)WS3000i88C Data Lead E7 Id)

WS2000 V211V23Manual Modem (92WS 2000 Auto Dial Card . E27 (dlINS 2000 Auto Answer £27 (diINS 2000 SKI Kit £5 IdlINS 2000 User Port Leed . E5 (d)

(Offer Erni:0d to current stocks)

SPECIAL OFFEREPROMs/RAMS

2764-25 £2.80 (d)27128-25 £3.60 (d)27256 £5.00 (d)27512 £9.90 (d)6264LP-15 . . . . £2.60 (d)

PROJECTS:Junior Computer Kit £86 lb)Housekeeper kit £58 (b)Elekterminal Kit (1980) £50 (b)ASCII Keyboard kit £75 (b)J C Books 1. 2. 3, & 4E6.90 Ic) eaUniversal Terminal (6502) Kit £75 (b)Elekterminal Kit (19831. _ £70 (b)

503-N Jnr. Computer Monitor2708 £ 4.80

504 Disco fights 2708 £ 4.80505 Chess Intelekt . 2.2716 £14.60506 J C Tape Monitor _ 2716 £ 7.30507-N J C Printer Mon & PME

2716E 7.30SOB J C Bus Control 82S23

-E 4.80

510 150 MHz Freq Meter 2.82S23E 9.60

514 Dark Room Computer 2716 E 7.30

BOOKSNo VAT on

LANGUAGES:R502 Assy Lang Prog £19.958086 Book £23.95Acorn BCPL User Gude £15.00Acorn FORTH E7.50Acorn USP 7.50Acorn ISO Pascal Ref Manual_ _E10.00Intro to COMAL £10.00Intro to LOGO £7.50Micro Prolog Ref Manual ... £10.00Introduction to Turbo Pascal. (14.95Prog the Micro with Pascal . £8.50The UNIX Book E7.50Unix User Guide £19.95Understanding Unix £18.45

BBC MICRO GUIDE BOOKSBBC User Guide Acorn E15.00BBC Plus User Guide . £15.00Drawing your Own 88C ProgramsE6.95Inside Information E8.95Meth Rog in BBC Basic _ _ _ _

(10.95E7.95Toolbox 2VIA 6522 Book 4.50

PROGRAMMINGIUTILITYAdvanced Sideways Rant UserGuide E9.95Advanced User Guide (BBC)... £12.50Applied Ass. tang on the BBC £9.95BBC Micro Sideways ROM's RAMsE9.95Guide to the BBC ROM £9.95Beginners Guide to W.P £7.95

books; Carriage (c)3.0 User Gwce . £10.00

%I-rev:store £10.00Viawsheet E10.00Wordwise Plus £9.95

SOUND & GRAPHICS:Mastering Music E6.95

DISC DRIVE SYSTEMS:Advanced Disc User Guide ...Disc BookDisc Programming TechniquesDisc SystemsF -de Handling on the BBC

£14.95E3.50£7.95E6.95£6.95

APPLICATIONS:Interfacing Proj for BBC £6.9589C and Small Business (5.75

PROFESSIONAL SOFTWAREWords -tar made easy £16.95Introduction to Wordstar £17.95Wordstar Handbook £11.95ciBase-II for the fast time user E16.95Understanding dBase.ei E22.95Multiplan Made Easy £18.95MtAtimate Complete Guide (16.95ABC of LOTUS 123 £17.45

£16.95£22.95£17.95£16 50

1-2.3 for BusinessAdv Tech in &Lased/111Mastenng CPiMCP.1,1 &tieIntroducing C.RM on BBC & Z80 E9.95P.1S,PC DOS Prompt £10.95

PROGRAMMED ROMS FOR ELEKTORPROJECTS

tto ia..-ng Dice 2716 E 7.30521 CharGen & Video Routine for DOSJunior 2732 + 2716 £16.40522 CharGen & video: Routine for ex-tended junior 2732 ÷ 2.2716 E24.00523 Char. Generator .. 2732 E 9.00524 Ouantisizer 2732 L 9.00525 Universal Term. 2732 E 9.00526 Wind Dir Ind 2716E 7.30527 Elabyrinth 2716 f 7.30530 Daisynheel Iface 2 2716 £11.00

ALL PRICESEXCLUDE VAT.Please add carriage 50p unless

indicated as follows:

(aJf8 01E2.50 lc -1E1.501 talf1.00

TECHNOLINEVIEWDATA SYSTEM

Tel. 01-450 9764Using 'Prestel' type protocols.

For information and ordersavagable 24 hours. 7 days

a week.

SEE OUR PAGE 5 ADVERTISEMENT FOR COMPONENT PRICES

TECHNOMATIC LTDMAIL ORDERS TO: 17 BURNLEY ROAD, LONDON NW10 lED

SHOPS AT: 17 BURNLEY ROAD, LONDON NW10(Tel: 01 208 1177, Telex 922800)

305 EDGWARE ROAD, LONDON W2, Tel: 01 723 0233

PLEASE ADD CARRIAGE AS PER CODE & 15% VAT

(Export: no VAT. pap at Cost)Orders from Government Depts.& Colleges etc welcome_

Minimum telephone order £5.Detailed Price list on request.

I Prices subject to change without notice .*please mention ELEKTOR ELECTRONICS when contacting advertisers

CONTENTSOctober 1987Volume 13Number 149

13 Editorial14 Electronics News17 Telecommunications News20 Computer News

Technologists look to Britain inEurope's great Eureka project.p. 62

14 -bit D -A converterp. 38

INFORMATION48 Events; 56 New literature;63 New Products; 70 Readers'services; 70 Corrections; 72Terms of business.

GUIDE LINES73 Buyers' guide; 75 Switch-board; 78 Small ads;78 Index of advertisers.

ELECTRONICSTECHNOLOGY22 High -current switching regulator IC

simplifies supply design: a 2.5 A power ICthat reduces the cost of power supplies.

24 Electronmicroscopy comes to life: a newtechnique is paving the way to observingthe dynamics of life at high magnifications.

28 Filters - theory & practice Part 3: the finalpart of the article deals with the practicaldesign of modern filters.

49 Switch -mode power supplies: a discourseon the design principles and practicalaspects of these modern power supplies.

54 The positive impedance converter: A.B.Bradshaw describes a practical means ofsimulating inductance in AF circuits.

58 Research collaboration to boost IT: closerlinks are being forged in Britain betweenresearch and product development.

59 The desk -top supercomputer: modular con-cepts of computer structure will cut com-puting costs by some 90 per cent.

60 Background to hollow emitter technology:this technology, lying midway betweenbipolar and MOS technologies, provides aneconomic solution to high -voltageswitching.

62 Technologists look to Britain in Europe'sgreat Eureka project: a look at this import-ant research and development programme.

PROJECTS32 IEC-Centronics interface: a unit to ensure

correct timing of handshaking signals whenan IEC or IEEE bus is used to drive a Cen-tronics device.

36 Low -noise microphone amplifier: a qualitypreamplifier that can be used with high -and low -impedance, balanced and un-balanced microphones.

38 14 -bit D -A converter: a device that enablescomputer control of test, measuring, andelectrophonic equipment.

44 Record -playback amplifier: enables slidepresentations with spoken commentary ormusic while a separate track on therecorder is used for controlling the slidechanger.

46 SSB adapter: a low-cost add-on unit forSSB reception on virtually any AM short-wave receiver.

In our Novemberissue: Infra -red

transceiver Precise motor

speed regulator The birth of space

communications Digital audio tape Morse code

teachingprogramme forAcorn/BBC com-puters

Second -user testequipment review

Short-wavereceiver

Front coverProof of the ex-istence of supercon-ductivity: a disc ofsuperconductivematerial is freelysuspended above amagnet by theMeissner effect.When the disc isheated by the sur-rounding air, it losesits superconductivityand drops onto themagnet.(Photograph bycourtesy of FOM/Picture Report)

EE

October 1987

MULTIMETERS

Can'4?pill:4410S"'""

DM105 .c1 -£21.5C1A meter to suit ail pockets.=turfing the one that hotds thewand( Full complement ofrangim. 2V -1W DC.200V -750V AC. 2mA-2A DCcurrent and 2k -2M resistancerange Basic accuracy 05%

AffordableAccuracy

A comprehensive range ofquality Multimeters at verycompetitive pricesDIGITALAM models feature full ranges. 31/2 digit0.5 in LCD. low battery indication. autozero and auto polarity, strong ABScasing. 10 Amp range (except DM105).overload protection. Prices from £21.50to £52.50. Battery, spare fuse. test leadsand manual included with each model

ANALOGUEA choice of four meters with pricesranging from £5.50 to £21.00. Allmodels include battery, test leads andmanual.

Please add 15% VAT to allprices and 70p for post and

Chidpacking. EtAccess

Phone or write for fullCirkit Distribution Ltd. catalogue price £1.20 to

Park Lane, Broxbourne, Herts EN10 7NQ.Telephone (0992) 444111.

BUILD THE ELEKTOR VALVE PREAMPWITH COMPONENTS

1114 Aft

VISIT AUDIOKITSSTAND AT THE

HI -Fl SHOW,HEATHROW PENTAHOTEL, SEPT. 19th

Ft 20 th 1987

AND ENJOY SOUND QUALITY EVEN BETTER THAN THE ORIGINALIf you want the very best sound quality from an amplifier, you must use compo-nents of the highest quality. Standard 1% metal film resistors give a good perform-ance at a low price, but the Holco range of precision metal film resistors actuallysound so much better that AUDIOKITS sells hundreds each week to audioenthusiasts who are building new amplifiers or replacing the resistors in their exist-ing amplifier. At a typical price of 35 to 40 pence, can you really afford to use lowerperformance resistors? And for really high quality applications (such as the Elektorvalve preamp) AUDIOKITS is selling more and more Bulk Foil resistors at prices of£4.50 - £22 each.

January's Elektor gave an excellent summary on capacitors. AUDIOKITS suppliescapacitors of the very highest audio quality including lAR Wonder caps, close toler-ance polystyrenes up to lOOnF and grade 1 long life electrolytics.

AUDIOKITS sells high quality semiconductors including MATO2FH 1f8) andOP27GZ (£825) for use in the state of the art preamplifier; also OP5OFY 1E14_001,OP77GP (600V offset, (2.75), OP77EP125uV offset, £6.50); also Bourns conductiveplastic stereo pots, silver and gold plated switches, gold plated phono sockets.Kimber cable and much more.

To help you build the Elektor Valve Preamp or State of the Art preamp withAUDIOKITS components, AUDIOKITS are producing two technical notes whichinclude prices of components and advice on where to get better sound quality fromhigher quality parts. Price £2 each.

For full details of AUDIOKITS components and services, including some of the verybest complete amplifier kits avaRable, please send 9" x 4" SAE to:

AL.PDHOVOITR, PrrscEPrnn6, Mill Close, Borrowash, Derby DE7 3GU, England

Tel. 0332 674929

NEW THIS MONTHJUST ARRIVED!!A major electronic distributors discon-tinued lines. all being sold off at LESSTHAN 'A PRICE!! - boxes, cases, con-nectors. LED's switches, DIP boards,cable ties etc_ All goods detailed in a16 page supplement available nowFREE

Examples:Briefcase type combination locks

E4.71 per osirSloping front cases:

161 x 96 x. 57139mm 92p215 x 130 x 73!47rnm £1.49

Plastic box with PCB slots190.110.60mm £1.40Large steel case 336 x 269 x 148mm

£15.45'Tidyman' Kits: Contain a wide varietyof support pillars, stand offs, cablestraps and clamps etc 146 duff) all in at-tractive plastic case.Small: (201 total) £7.80: Large 1708total) £13.00Full details in Supplement. 1Post £2 onall above)

- e

Z652 Coin acceptor mechanism. Madeby Coin Controls, this will acceptvarious size coins by simple adjust-ment of 4 screws. Incorporates varioussecurity features - magnet, bent coinrejector etc. Mictoswitch rated 5A240V. Front panel 115 .64. Depth130rnm. Cost £10.85.Our price £4.00CREAM DISPENSERZ801 Coin opers-.e.c machine for dis-pensing hand Cabinet 620 x.365 x 200mm. 0kg. contains coinmech, PCB. co..--_- pump mech con-sisting of h:;- 7 = geared 6V motordriving [amt.:" cream. & sens-ng = nowered bvnal 6V 2.6A re::-argeatle ta::,rry

£15 -Parts available separs:s:,. Se= 30SPEECH CHIPZ733 SP0256A +, index chip - ULAchip as used in Currah microspeech_Cct and info fur using SP0256 withSpectrum. 2X81. BBC. VIC & C64. Noinfo on other 2 chips. All 3 for E3.00AUTO DIALLERSloping front case 240 , 145 90:50contains 2 PCB's: One has 4 keypads(total 54 switches) 14 digit LED dis-play. 2 x ULN2004, ULN2033 & 4067:the other has 12 chips - 4 powerdevices etc. Case contains speaker. 8core cable 2m long with plug. For usewith PABX. £9.00SWITCHED MODE PSUAstec type AA7271. PCB 50 50mmhas 6 transistor cc; providing currentoverload protection, thermal cut-outand excellent filtering. Input 8-24VDC. Output 5V 2A. Regulation 0.2%.£5.00

PANELSZ620 68000 Panel. PCB 190 .45 be-lieved to be from ICL's 'One per Desk'computer containing hiC68008P818MHz 16.8 bit microprocessor. - 4ROM's. all in skts: TMP5220CNL.74HCT245, 138, LSOB. 38 etc. £5.00

Z625 32k Memory Board_ PCB170 .170 with 16 a .x 8 6116 staticRAM's. Also 3.6 V 100 mAmernopack nicad, 13 other HC,LSdevices. 96w edge plug. 8 way DILswitch. R's. C's etc. £4.80Details of other similar PCB's in latest',sr

sinciairMICROVISION

CASES'!!We now have a supply of casescomplete with aerial at the specie'low price of £5.00We have a quantity of these unitsin varying states. From labels at-tached to some of the PCB's i:seems after assembly on the pro-duction line they did not functioncorrectly. No attempt has beenmade to repair them, though - instead the following parts wereremoved:

al RF Tunerbl Vol control & switchc) ZN401E chip

Z666 2 x PCB in good conditionwith 2 CRT that have been re-moved, but maybe repairatiTeConductive paint (15ml bor.I.r.£3.45) will probably be needed 17remake contacts. With diagram n.notes £6.95Z560 Circuit diagram and notes7 pages detailing tech. spec ce-scription, cct operatiop _ e_:-

nosis & repair, aid to !r_i_ 1 rcart, picture set up pfccec...7--PCB layout. info on the varic.,possibilities £2.00RF Tuner 1'6 95 7..-:£9.95: Vc: ------ ,knob `-1 OD

MOTOR - SOLENOIDZ659 Motor, high torque 6V operation

-:egral brass gearbox giving- =='.' Shaft 18mm long . 6mm die

Overall length exc. spindle- ,3mm. Ideal for robotics

r: being extremely hti-,£2-75

2738 solenoid single hole fix:-_46 16 18mm. Slug is 45mm long -

6.5mm dia with tapped cross hole andslot. 25mm pull. £1.75

SPEAKERS2578 Sub -min speaker 30 x 30x 3mmthick by Fuji_ 16R 0.4W. 60p ea; 10E3.70 25 E7: 100 E22; 1000 £180.Z575 70 .45mm 45R 0.5W 55p ea;10 £3.30 25 £6 100 £20

SOLDER500g reels resin cored. 18g £5.95500g reels resin cored 22g £7.95

LOGIC PROBEFor TTL, CMOS etc. LED and sound in-dication Pulse enlargement capabilityallows pulse direction down to25nsec. Max f = 20 MHz 4-16V. 1.1,Z:1M £9.99

'NEWBRAIN' PANELSZ494 Motherboard microprocessorpanel 265 x 155mm Complete PCB forcomputer. Z80. char EPROM etc_ 68chips altogether other associatedcomponents, plugs, skts etc £5.50Z495 RAM panel. PCB 230 x 78mmwith 14 x MM5290-2141161 (2 miss-ing) giving 28k of memory. Also 8 LSchips. These panels have not beensoldered, so chips can easily be re-moved if required £5.00Z679 Keyboard. 62 keys on allychassis 260 .90mm. No PCB £6.50Z670 Handbook 204 pp. Useful appen-dix (about *ri the book) gives tech. info

£5,00'NEWBRAIN' PSU

BRAND NEW Stabilized Supply inheavy duty ABS case with rubber feet.Input 2213:240V ac to heavy dutytransformer via suppressor filter_Regulated DC 7, -2A;13 -5VatO Allcomponents re,-,: . formods etc. Chunk,, has 2 xT(P31A. Mains lean h'.(tesc with 2 pincontinental plug) is 2m long. 4 coreoutput lead 1.5m long fitted with 6pole ski on 0.1" pitch. Overall size165 x 75 .72mm.

£5.95 ea 10 for £40

MEWGREENWELD

ELECTRONICCOMPONENTS

451)1"k -es indutle VAT; lust eOd Ko P&P.

or,tt,s frc-^.-. s.-to:,s et: Att.Min itccS ortt, E10 Official 1E3

. - - .. - .,...9e iliaC _ , __ . , . __.: ...:-:1 of components sna IS OPto

443E Millbrook Road SouthamptonSO1 OHX Tel 10703) 772501,783740

EE

October 1987

Managing Editor: Len SeymourPersonal Assistant: L. VousdenTechnical Editor: J BuitingAdvertisement manager: S Brooks

Editorial offices:1 Harlequin AvenueGreat West RoadBRENTFORDMiddlesex TW8 9EWEnglandTelephone: 01-847 2618Telex: 917490 (elektr gl

European offices:Telephone: 31 4402 89444Telex: 56617 (elekt nllFax: +31 4402 70161A Wolters A'luv.'ar Company

Overseas editions:Publitron Publicacoes Tecnicas LtdaAv ipiranga 1100, 9' andarCEP 01040 Sao Paulo - BrazilEditor: Juliano Barsali

Elektor sariRoute Nationale: Le Seau; B.P. 5359270 Bailieul - FranceEditors: D R S Meyer:G C P Raedersdorf

Elektor Verlag GmbHSasterfeld-Strage 255100 Aachen - West GermanyEditor: E J A Krempelsauer

Elektor EPEKaraiskaki 1416673 Voula - Athens - GreeceEditor: E Xanthoulis

Elektor Electronics PVT Ltd.Chhotani Building52 C, Proctor Road, Grant Road (ElBombay 400 007 - IndiaEditor: Surendra lyer

Elektuur B.V.Peter Treckpoelstraat 2-46191 VK Beek - the NetherlandsEditor: P E L Kersemakers

Ferreira & BentoR.D. Estefania, 32-1°1000 Lisboa - PortugalEditor: Jorge Goncalves

Ingelek S.A.Plaza RepUblica Ecuador2-28016 Madrid - SpainEditor: A M Ferrer

Electronic Press ABBox 63182 11 Danderyd - SwedenEditor: Bill Cedrum

International co-ordinating& technical manager:K S M ,,VairavenInternational editorial secretariat:GWPv Linden: M Pardo

Distribution:Seymour Press Ltd., 334 BrixtonRoad, London SW9 7AG.

Typeset & composed in theNetherlands by GBS, Beek (L).Printed in the Netherlands byNDB, Zoeterwoude.

Copyright = 1987 Elektuur B.V.

ABC

FORGOTTEN GENIUSREMEMBERED

Not many scientists have been treated as shabbily, or forgotten as quickly,by most of their countrymen as Alan Turing. Had our society in the 1940sand 1950s been as tolerant as that of the 1970s and 1980s, Turing wouldnot have committed suicide in despair at the early age of 42.

Yet, there were times when this brilliant mathematician was one of thecountry's heroes. That was during the Second World War when he led theteam at Bletchley Park that cracked the German Enigma Code andthereby assuredly helped to shorten the war.

The work at Bletchley Park into which Britain's best brains were drafted laidthe foundations for modern computer science and, more particularly, Ar-tificial Intelligence.

Alan Turing had been fascinated all his life by the idea of creating an in-telligent machine. Machine intelligence was foreseen as early as the 19thcentury by Charles Babbage, but it was not until Turing provided the theoryabout what questions could in principle be answered by such machinesthat artificial intelligence began to be researched seriously.

Machines to Turing were mathematical objects (as. indeed, they are nowto most researchers) and he was fascinated by the idea of determiningmathematical proofs with the aid of a universal computing machine. Sucha Turing machine can be used to determine the concept of computableand non -computable functions. Turing's main contribution to computingscience was his proof of a theorem that showed that the set of mathemat-ical tasks that is computable is exactly the same as the set that can beexecuted by the Turing machine.

It is gratifying that one of Turing's young colleagues at Bletchley Park. Pro-fessor Donald Michie, has taken up where Turing left off in 1954. ProfessorMichie led a group of researchers into artificial intelligence at EdinburghUniversity for over 20 years. A few years ago, the team moved to Glasgowwhere, with funding from the Scottish Development Agency and with thebacking of Strathclyde University, it has set up the Turing Institute. A fittingalbeit belated tribute to a man whom society did not allow to see hisvision come to fruition.

Thanks to Turing and his successors at the Turing Institute, Britain is still in theforefront of research into artificial intelligence, knowledge -based systems.and computer science.

The institute is a pioneer in inductive learning and is. indeed, a worldleader in this field. This invokes literally teaching the computer to learn foritself on the basis of its accumulative knowledge. Inductive programming isthe basis for knowledge -based systems, computer vision, and robotics.

It is, of course, true that there are people who fear that artificial intelli-gence will eventually deny our individuality and freedom. It is, however,equally true that research in artificial intelligence encourages a newrespect for the riches and power of everyday human mental processes. Isit, therefore, not a reasonable assumption that artificial intelligence willcounter the absence from the natural sciences of concepts like belief,reason, inference, purpose, and choice? Alan Turing would undoubtedlyhave been the first to welcome this aspect of artificial intelligence.

..sysEqK.-FEAU Cg- CAP.:iATOYS

EE

October 198714

ELECTRONICS NEWS ELECTRONICSEurope'selectromagneticcompatibility marketThe growing complexity anddensity of electronic equip-ment in military and aerospacevehicles and systems arecreating a greater awareness ofproblems associated with elec-tromagnetic interference, andgenerating a burgeoningEuropean market for elec-tromagnetic compatibilityproducts and services.Frost & Sullivan's report Elec-tromagnetic CompatibilityProducts and Services Marketin Europe (#E892) forecasts thismarket to expand from $194million in 1986 to $511 million by1993: an overall average annualgrowth rate of 14.8% in constant1986 US dollars.The report analyses the marketfrom a number of standpoints:by materials, products, and ser-vices; by applications; byOEMs and end -users; by size,industry structure, and nationalcharacteristics.In both service and productcategories, the UK will continueas the leading market, followedclosely by Federal Germany,and France third. The UK is theonly country in which in-digenous manufacturers out-number foreign distributors (93

to 39). In western Europe as awhole, there are 193 indigenousmanufacturers and more than250 distributors representing124 non -European companies.

BARTG AGMThe Annual General Meeting ofthe British Amateur RadioTeleprinter Group will be heldon Saturday 7th November at1400 h in The Churchill Room London House Mecklen-burgh Square London WC1(junction of Guildford Streetand Doughty Street, close toKing's Cross). Further infor-mation from Ian Brothwell(Secretary and Publicity Of-ficer) BARTG 56 ArnotHill Road Arnold NOT-TINGHAM NG5 6LQ.

Plating tin on tinMega Electronics can nowsupply a powder -form tinningsolution that is the only one cur-rently available capable ofplating tin on tin. This SENO-TIN solution has a number ofunique features important inPCB production.In addition to its ability to platetin on tin, SENO-TIN is de -

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SALES OF ELECTROMAGNETIC COMPATIBILITY

PRODUCTS & SERVICES FROM WESTERN EUROPE

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signed to work at room tem-perature, which means that thetinning process may be carriedout in unheated trays or othercontainers. It produces a tinplating of between 1.5 and2.0 pm in the first half hour, and4.5 pm in up to two hours. Thepowder may be mixed in or-dinary tap water, after which ithas a shelf life of around sixmonths. Its shelf life in powderform is indefinite.Shown in the photograph is anenvironmentally -safe dispos-able applicator, using theSENO-DEVELOPER, for theprototyping of PCBs.More details from Mega Elec-tronics Ltd 9 RadwinterRoad Saffron Walden CBU3HU Telephone (0799) 21918.

SchlumbergerTechnologiesIn a recent company reorgan-ization, the Schlumberger Corn-

puter Aided Systems andInstruments Divisions weremerged into SchlumbergerTechnologies headed byExecutive Vice PresidentMichel Guilloud.The two merged divisions, ex-cluding the transducer busi-ness, which is part of Schlum-berger Industries, are part ofSchlumberger's Measurement& Systems business segment.Also, CAS group members Sen-try and Factron are now com-bined into the Automatic TestEquipment unit of Schlum-berger Technologies.Schlumberger Technologieshas its headquarters at Sun-nyvale, California, and researchlaboratories in Palo Alto,California. It consists of high-technology business in the areaof computer graphics, instru-ments, computer aided designand manufacturing, and auto-matic test equipment.

Fieldtech Heathrow can supply the Meguro MAK-6581 AudioAnalyser, which incorporates the functions of an audio oscillator,distortion meter, SIN meter, and can store in RAM up to 100 frontpanel settings. Details from Fieldtech Heathrow ltd HuntaviaHouse 420 Bath Road LONGFORD U87 OLL Telephone01-897 6446.

1!1 EE

October 1987

ELECTRONICS NEWS ELECTRONICS N]Shaft angle encoderThe maximum output signal fre-quency of the new shaft angleencoders from Siemens (seephotograph) has been im-proved from 100 kHz to 300 kHz.

The outward appearance of thedevice remains unchanged.The shaft angle encoders,powered from a 5 V supply,deliver two TTL compatible out-put signals, electrically phase -shifted by 90' with a resolutionof 60 to 5000 pulses per revol-ution. Once per resolution anadditional pulse is delivered fordefining the zero point.

Quick IC replacementThe Dipmaster Rework Systemfrom TOOLRANGE savesvaluable time in delicateintegrated -circuit and connec-tor rework. Even non-standardcomponents can be removed,replaced, and resoldered fromthe component side of the

board without damage to eitherthe board or the component.The Dipmaster System hassolide-state temperature con-trol within the range 150 CC to450 °C and zero -voltageswitching, so that sensitivecomponents, such as MOSFETs,can be worked on in perfectsafety.Details from TOOLRANGELTD Upton RoadREADING RG3 4JA Tele-phone (0734) 429446.

New ERA laboratoriesERA Technology's researchand development capabilitywas further expanded in theearly summer with the openingof new laboratories and officesat its Leatherhead site. Thismarked the completion of thecompany's £3 million expan-sion programme, bringing thetotal facilities to 25,000 mt.The new building, the centre-piece of a development that in-cludes an improved road sys-tem and an additional car parkfor 163 vehicles, was formallyopened by Their Royal High-nesses the Duke and Duchessof York.Main occupants of the newblock are the Radio FrequencyTechnology Division whose ac-tivities include the design,manufacture, and testing ofmicrowave antennas for satelliteand ground communications.The division can now claim tohave some of the most ad-vanced facilities in Europe for

the development of radar andcommunications antennas,specialist radio frequencyproducts, active microwave cir-cuits, and space -approvedhardware.

New breed of pulse ca-pacitor from ERAResearch and developmentconducted by ERA Technologyhas resulted in a new gener-ation of high -voltage pulsecapacitors. Designed for highreliability and long life, theseextremely compact energystorage capacitors are intendedprimarily for firing lasers, butare also suitable for manysimilar applications where HVpulses are required.ERA has produced capacitorswith ratings as high as 15 nF at35 kV and as low as 1 nF at16 kV. Overall energy densitiesfor capacitors of higher ratingsare well over 60 mJ cm' with alife of more than 100 millionhalf -microsecond non -revers-ing pulse. Pulse repetition ratescan be up to 100 pps at an am-bient temperature of 85 C.

PCB protectionagainst ESDSchlumberger ATE's new DISS-STAT vacuum fixture for in -

circuit automatic test equip-ment protects PCBs againstdamage from static discharge.This new product, the firstavailable for ATE users,eliminates electro-static dis-charge (ESD) caused by air flowacross insulating surfaces, or by

movement of test fixture parts. Itprotects components on thePCB from complete or partialfailures caused by high -voltageESD or lower -voltage "elec-trical overstress", providing amanufacturing solution capableof meeting the most stringentquality and/or military ESDstandards.

Time in handA Digital Quartz Timer withclock, calendar, alarm, andstopwatch modes is availablefrom TMIC. This hand-helddevice, which can also be wornaround the neck by its integrallanyard, is easy to operate, light,rugged, and comes ready foruse with operating instructions.

It is art ideal tool for Technical,Business, Sport, Hobby, andLeisure applications. Its price is£11.95 plus VAT, and it isavailable from Harris Elec-tronics (London) Ltd 138

Grays Inn Road LondonWCIX 8AX Telephone 01-8377937.

16

'ELECTRONICS NEWS ELECTRONICS 1%11Elektor Kits & PartsD.R. & J.G. Taylor, one time kitsuppliers for Elektor projectsstill have a number of Elektorprinted circuits in stock, includ-ing Elekterminal and DiscoLight Controller. They also havea supply of componentsspecifically for a variety of kits,and stock a range of other com-ponents. Enquiries should beaddressed to D.R. & J.G. Taylor(Services) HolmhtustChurch Street Rudgwick West Sussex RHI2 3ET.

Culham Laboratory winsanother US contractCulham Laboratory of theUKAEA has won another majorcontract worth nearly half amillion pounds from the UnitedStates for supplying specialistmeasuring equipment for afusion research experiment.The contract forms part of thelaboratory's expanding com-mercial research programmeswhich have increased by 40% inthe past year.The contract has been placedby Princeton University onbehalf of the United StatesDepartment of Energy. Prince-ton is the major research centrein the United States for PlasmaPhysics and Fusion Research.Under the contract, Culham willdesign and manufacture a diag-nostic beamline which will beused to measure impurities inthe Princeton Beta Experimentby probing with a small intensebeam of fast atoms.In the photograph, Ian Gray,

Henry Kugel (Princeton) andJim Coupland examine a com-puter model of the DiagnosticBeam Line for Princeton on oneof Culham Laboratory's CADterminals.

LONDON ELECTRONICSCOLLEGEThe London Electronics Col-lege is launching a new seriesof up -dated one year full-timeBTEC National Certificatecourses from 21 September1987. The subject specialismsavailable will be Electronic equipment ser-

vicing; Computing technology; Information technology; Software engineering.

These courses are particularlyimportant for those wishing toupdate or re-train, either withEmployer sponsorship (up to£1,000 ATS grant aid) or forthose recently taking re-dundancy.The college is also a ManagingAgency for the M.S.C. Job Train-ing Scheme (ITS) and willrecruit suitable applicantsdirect onto the new JTS. Thisprogramme involves periods ofJob training and work ex-perience in industry; em-ployers interested in takingtrainees for 3 to 6 monthsshould also contact the Col-lege. (Trainees will receive afull training allowance from theMSC).Other courses available includea two year full-time BTECNational Diploma and a one

A new compact high -quality 1 kW amplifier, the JERICHO, designedto meet the requirements of the public address and industrialmarkets, has been announced by Tunewell. Further information fromTunewell Transformers Ltd 115a Myddleton Road Wood Green LONDON N22 4NG.

year full-time BTEC HigherNational (Computing Tech-nology, Control and Robotics).Short courses from 1 to 3 weeks(VCR servicing and Microcom-puter servicing) are also run-ning. The EITB Certificate ofBasic Technician training (Elec-tronic Engineering Appli-cations and EngineeringSoftware Applications) may alsobe awarded.For details and prospectus, con-tact M.D. Spalding, BSc, MSc,PGCert,ED., CEng, MIEE Principal The London Elec-tronics College PenywernRoad LONDON SW5 9SU.

PEOPLEEarlier this year, Mr Jean LouisCoulon was appointed Manag-ing Director of Bull CP8. Anative of Ajaccio, Mr Coulon,50, holds a License et Sciencesdegree from the Sorbonne andis a graduate of the Institut deControle de Gestion.

At their recent Annual GeneralMeeting, the British AudioDealers Association (BADA)elected the following newexecutive members.Jerry Lewin of Absolute Sound

and Video takes over fromKevin Maxfield as Chairman.Graham's Hi-Fi's MichaelLewin becomes Vice Chair-man: Dereck Aston Darker ofAston Audio, Treasurer; Hamp-shire Audio's David Block,Membership Officer; and Jef-fries Hi-fi's Kevin Maxfield, PROfficer.

Printronix has appointed IanTrew (see photograph) as Tech-nical Applications Managerwith special responsibilities forsecuring and supporting OEMbusiness. He will be based atthe company's new head-quarters in Woodley nearReading.

EE

October 1987

TELECOMMUNICATIONS NEWS TELECiNew -generation radiotelephoneIn -car radio -telephone usersare given a wide range of op-tions with a new synthesizedtwo-way AM/FM equipmentfrom Tactico. This mobile radio-telephone, the Type MR225, hasbeen designed for all channelspacings from 6.25 kHz. Fre-quency synthesis removes theneed for channel crystals andallows fast, economical pro-gramming with the aid of aplug-in EPROM.Further information fromTactico Ltd 65 Logie GreenRoad EDINBURGH EH7 4HF Telephone (031 556) 6167.

First flat -screen TV inEuropeThe first European televisionset with a completely flatscreen has been developed inFinland. Most currentlyavailable flat -screen TV setshave a screen size of 5 to 8 cm.They generally use liquidcrystal techniques and arealmost exclusively Japanese.The Lohja Corporation's FinluxFace has an 18 -cm screen and isbased on the company's elec-troluminescent display tech-nology. This technologyenables the image on the TVscreen to be clearly visibleeven in the presence of strongambient lighting. Lohja havealso taken into account the

future change in aspect ratiofrom the present 3:4 to thewider 3:5.3 high -definitionnorm.Other interesting features of theFinlux are that in a very smallset it offers stereo TV, teletext,and the capability of receivingall current TV standards. It isremotely controlled and, sincethe screen is only 2 cm deep, itcan easily be hung on the wallor placed on a table.Commercial sets will not beavailable until the end of theyear.

Euro-MAC for satellitetelevisionA European consortium formedby Logica, Fuba, ITT In-termetall, Salora-Luxor, Philips,and Thomson-CSF, has com-pleted its specification for apan-European satellite broad-cast television system calledEuro-MAC.The Euro-MAC consortium wasformed last year with the inten-tion of developing a system thatwould resolve the currentdebate over variants of the MACtelevision standard, which hasso far threatened the success ofsatellite broadcasting.Important aspects of the designinclude the fast delivery of de -scrambling messages to Pay -TVreceivers and the provision ofhigh -quality multi-lingualbroadcasting allowing theviewer to select the appropriate

language. The system could beused for satellite broadcastingwith or without controlled ac-cess to Pay -TV, and in the futurecould be implemented in homevideo recorders. The designalso makes allowance for futureapplications such as wide-screen displays and high -definition television.The consortium's system wouldbe able to provide individuallycontrolled access for the 150million potential viewers ofEuropean television. It will ex-ploit the new MAC technologyfor television with Euro-MAC,which is a derivative of theEuropean Broadcasting Union'sMAC/Packet family of systems.Logica will supply audiencemanagement systems, whileFuba will supply the encoders.Together, these elements willmake up the complete trans-mission systems. ITT In-termetall will supply integratedcircuits for the decoders, andPhilips, Thomson, and Salorawill manufacture set topdecoders and fully integratedsatellite television receivers.The system will be marketedjointly by all the members of theconsortium, but its specifi-cation will be made public, sothat all manufacturers can par-ticipate.The aims of the consortium areto create a unified EuropeanSatellite Television Trans-mission and ScramblingSystem, so that consumers needpurchase only one receiver andaccess system to be able toview the satellite programme oftheir choice. Programme pro-viders will, therefore, share thecost of the development of asingle system that will give ac-cess to all their programmes.

Business Televisiongoes BASYSBusiness Television, which hasjust started to produce a dailybusiness news for Channel 4,has installed a BASYS newsroomsystem. This brings the numberof BASYS sites world-wide toover 130. In the UK, all televisioncompanies who have com-puterized their newsroom oper-ations have installed BASYS inpreference to other systems. In

Europe, users of the BASYSsystem include the Swiss Broad-casting Corporation, the Fin-nish Broadcasting Corporation,RAI, the Italian State Broad-casting Company, TVES inParis, and AFN in Frankfurt.

New matrix panelA range of CTCSS SignallingPanels for mobile radio appli-cations is now available fromCommunication DevelopmentSpecialists Ltd. Many of these

panels are controlled by a rowof six links or diodes. With thisconfiguration, it is not possibleto remotely change the pro-gramming information. Thisproblem is overcome by the six -channel matrix panel.

Electronic Brokersenters fibre optic testmarketElectronic Brokers has enteredthe fibre -optic test market withthe Thorn EMI Megger range ofhandheld optical light sourcesand power meters. Together,these instruments can be usedto investigate attenuationcaused by connectors, splices,and the fibre itself.

October 19E8E7

TELECOMMUNICATIONS NEWS TELECINorth American satellitecommunications marketSending microwave signalsfrom one earth station toanother halfway around theworld costs no more, via com-munication space satellite, thansending them 100 miles-andno area is too rugged or remoteto receive them. Up to 6.3million bits of digital data canbe sent in one second. Minimalatmospheric interferencemakes the error rate only aboutone error per 100 million bits.Such clear-cut advantages havehelped commercial satellitecommunications burgeon overthe past 25 years. Yet, from arevenue standpoint, the reallygood years lie just ahead, ac-cording to a new Frost &Sullivan report: The SatelliteCommunications Market inNorth America-CommercialSystems, 1987-1996. (#A1739).The report sees annual earthstation sales expanding (in con-stant 1987 dollars) from $832million in 1986 to $3.4 billion in1991, peaking at $4.4 billion by1995, and then decreasing to$3.7 billion in 1996.Space segment revenues areforecast to rise from $869million in 1986 to $1.9 billion in1991, and to keep on growing to$2.5 billion by 1996. Thesefigures include the portion ofinternational systems (IN-TELSAT and INMARSAT) at-tributed to North Americancountries, as well as revenuesfrom US, Canadian, and Mex-ican domestic satellite systems.

Spacecraft sales-taking intoaccount the current launchproblems-are predicted togrow in dollar value from about$100 million in 1986 (only 2 com-mercial spacecraft launched) to$600 million by 1992 (12

spacecraft), the sliding to $350million in 1996 (7 lower -costspacecraft).Assuming an average launchcost of $40 million, total launchexpenditures are expected toincrease from $80 million in1986 to S480 million in 1992, thendecrease to $280 million by1996. Owing to launch failures,insurance rates have risen to20% (from about 8% in 1984).With more successful launches,the rates should drop to a levelof about 10% by 1996.

Big four useMarconi's ACEThe four largest networkoperators in the country havechosen Marconi Communi-cation Systems' AutomaticCross -connect Equipment-ACE-to provide networkmanagement facilities and in-crease the flexibility and ef-ficiency of their networks. ACEis already in service with BritishTelecom and Mercury Com-munications, and now thecellular network operatorsCellnet and Racal Vodafonehave ordered it. The total valueof these latest orders is around£1 million.ACE is used to automate the

SATELLITE COMMUNICATIONS MARKETIN NORTH AMERICA - 1986

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routeing and supervision of in-dividual 64 kbits/s timeslotswithin 2 Mbit/s channels. AnACE can be situated at the hubof a network of up to 4,000 cir-cuits, or any number of ACEsmay be distributed throughouta network and their operationco-ordinated from a remotecontrol equipment-RCE. Mar-coni's ACE (Type U4200) com-prises a TDM switching equip-ment in which the routeing oftimeslots is controlled by micro-processor from the RCE. Theequipment takes in 2 Mbit/ssignals and demultiplexes themto individual timeslots, which itthen connects to the timeslotsin 2 Mbit/s outgoing routes to apresent pattern. Routeing canbe provided on the basis ofunidirectional point-to-pointcircuits, both -way point-to-pointcircuits, unidirectional to multi -point circuits, and n x 64 kbit/scircuits.The equipment is based on asingle -stage, non -blockingtime -space switch employingLSI. The switch plane and its associated microprocessor con-trol are each duplicated,leading to high systemavailability. The maximumswitch configuration is a 128(2 Mbit/s) port timeslot matrix,but line equipment and switchshelves may be sub -equippedfor 32, 64, or 96 ports.

RADAR - 87An International Conference onRadar (RADAR - 87) will beheld at the Royal Borough ofKensington and Chelsea TownHall, London, on 19-21 October1987. The conference is beingorganized by the Institution ofElectrical Engineers (IEE) in as-sociation with the Institute ofElectrical and ElectronicsEngineers (Aerospace andElectronic Systems Society).Papers from 15 countries will bepresented at the conference,and a number of visits havebeen planned for Thursday, 22October. Establishments it ishoped to visit are: Royal Signalsand Radar Establishment, GreatMalvern; Admiralty ResearchEstablishment, Portsdown; GECMarconi Research Centre,Great Baddow; Plessey Radar

Ltd, Isle of Wight; Departmentof Electronic and ElectricalEngineering, University Col-lege London; and MEL,Crawley.A cocktail party for RADAR -87 registrants will be held at theScience Museum, London, onMonday, 19 October, when thespace and land transportgalleries of the museum will beopen for attendees.

Fibre optic links testingA new Optical Time DomainReflectometer (OTDR) fromSolartron, a division of theSchlumberger Group, offers ahigh degree of automation tosimplify and deskill opticalfibre testing.

Versions of the meter areavailable for a variety of opticalfibre types. All are designed tofacilitate bandwidth and at-tenuation measurements duringinstallation and maintenance oftelecommunication and LANlinks, as well as test and lengthmeasurement of cables duringproduction.

New Thorn EricssonfactoryThorn Ericsson Telecommuni-cations' new factory onHumberside was formallyopened recently by Sir GeorgeJefferson, Chairman of BritishTelecom.The factory, one of the world'smost streamlined productionlines, makes AXE10 digital elec-tronic telephone exchangesand other equipment for BritishTelecom.

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October 1987

TELECOMMUNICATIONS NEWS TELEC1

3Com Corporation andBridge Communicationsto merge3Com Corporation and BridgeCommunications, Inc., manu-facturers of network -basedworkgroup computing systemsand general purpose local areanetworks (LANs) products, re-spectively, have announced adefinitive agreement to mergethe two companies.

New signal processorfor F-15 aircraftA smaller and faster signal pro-cessor for the new tactical radarbeing fitted to F-15 fighter air-craft has been developed byHughes Aircraft Company,Radar Systems Group, of LosAngeles.The airborne signal processor,now in production for thecompany's APG-70 radar, packsthe power of 200,000 personalcomputers into a space of lessthan 1 cubic foot (28.3 dm'). Inthe photograph, a Hughes Air-craft Company systems en-gineer checks an electronicmodule in the processor.

The new signal processor is aspecialized computer that usesgate arrays-advanced verylarge scale integrated circuit-to help perform more than 34million complex operations persecond. Compared with itspredecessor used in the F-15'radar system, the unit is fivetimes faster and provides tentimes more memory.

SKYNET 4: the military com-munication payload for thisseries of satellites was de-signed, developed, andmanufactured by Marconi SpaceSystems, who are alsoresponsible for providing groundcontrol equipment.

Interface converterSweden's Westermo Teleindus-tri has launched an interfaceconvener that can also functionas a local network interchangefor up to 32 devices. The con-verter, Type MA -42, can also beused for local communicationover distances up to 1.2 km.Transmission is asynchronousat speeds up to 100 kbit/s.The photograph shows the con-vener with at its left the plug-inversion, Type MA -49.

Satellite radiopagingtrialsBritish Telecom will commencetrials of the world's first satelliteradiopaging service towardsthe end of this year.The service will provide radiolinks between British roadhaulage firms and their long-distance lorry drivers en routeacross Europe, the Middle East,and Africa. The system wasdeveloped by British Telecom.Messages sent by the inter-national radiopagers will betransmitted via BTI's satelliteearth station at GoonhillyDowns to an INMARSAT satel-lite. The signal will bedelivered to a small purpose-built antenna on the roof of alorry's cab and linked to apager and printer situated onthe parcel shelf of thedashboard. Messages to lorrydrivers can be telephoned orkeyed in.This satellite application is the

latest international extension ofexisting radionaging servicesoperated in the UK by BritishTelecom Mobile Communi-cations (BTMC). Later this year,BTMC will launch a transatlan-tic paging service, jointly oper-ated, with Metrocast, a UScompany, using a pageremploying earth -bound trans-mission.

Marconi satellitecommunications forGerman NavyMarconi Defence Systems haswon a contract to supply threeSCOT satellite communicationsterminals to the FederalGerman Navy.The terminals to be suppliedare the latest SCOT lA versions,similar to those currently onorder for the Royal Navy undera £40 million contract.SCOT IA accommodates thetransmission and reception ofspeech, telepgraph. data, andfacsimile traffic, and is fullyinter -operable with all currentand planned US, NATO, and UKmilitary communications satel-lites.It is the latest version of equip-ment that revolutionized navalcommunications planning inthe 1970s by offering immediateand secure long-distance satel-lite links that matched the qual-ity and reliability hitherto onlyobtainable from terrestrial line -of -sight equipment.

EE

October 198720

OMPUTER NEWS COMPUTER NEWS .Altos on the busesDeregulation of the bus in-dustry has led to a clutch oforders for Bewley Carlaw Com-puter Systems of Billingham,Cleveland, a value-addedretailer of Altos multi-usermicrocomputers supplied byLogitek PLC.The Bewley Carlaw package in-cludes modules for stock, per-sonnel, payroll, vehiclerecords, route costing, routemileage, bus ticketing systems,income analysis, and standardledger items. This gives the busoperators a much tighter con-trol over operations andenables them to handle theirown financial management.Previously, accounting oftencame under the local authority.

Miniature plain -paperprinter moduleCrotech Instruments' TypeMP -280-40 miniature printermodule, which is capable ofprinting 40 characters per lineon 69 mm wide plain -paperrolls, is ideal for use in instru-ments and other equipmentwhere space is an importantconsideration.The dot matrix is 5 x 7 and pro-vides a graphic point density of240 per line. Print speed is 4 dotlines per second. Power supplyrequirement is ±5 V; theaverage motor current is200 mA, with a peak needlecurrent of 2.5 A. The small di-mensions of the module(103.6 x 15.4 x 45.5 mm) allow it tobe incorporated into compactsand portable packages.RRP for the MP -280-40 is £48.94

and for the "packaged" ver-sion, the MP284-40, £72.15. Bothprices exclude VAT.Further information fromCrotech Instruments Ltd 2Stephenson Road St. Ives Huntingdon Cambridge-shire PE17 4WJ Telephone(0480) 301818.

Microcontroller develop-ment systemA PC -based full -function devel-opment system for Intel's8031/32, 8344, and 8051/52families of microcontrollers isavailable from Ashling Micro-systems: the Type CTS51.

The system operates with anIBM PC, XT, AT, or true compat-ible, via the RS232C interfaceunder MS-DOS. The family ofsystems provides developmentsupport for a wide range ofmicroprocessors and micro -controllers, with quick and easyupgrading to support other pro-cessors at moderate cost. Forinstance, the CTS51 with the ad-dition of an identity board and

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software package will also sup-port the Siemens SAB80515family.

Further details from AshlingMicrosystems Ltd Enter-prise House Plassey Techno-logical Park LimerickIreland Telephone 353 61334466.

3 + network forMacintosh3Com Corporation has com-menced delivery 3+ for Macin-tosh, an extension of its popular3+ network operating systemthat allows the integration ofMacintosh computers and IBMPCs and compatibles in a high-performance workgroup sys-tem.The new product allows usersof Macintoshes and IBM PCsand compatibles to share thefull range of the most powerfulnetwork services under 3+,available previously only to IBMPC, PS/2, and compatible com-puters.

Graphics spreadsheetfor signal analysisA version of the DADiSPWorksheet. the first technicalspreadsheet software for digitalsignal processing is nowavailable in the UK from AdeptScientific. DADiSP (Data Ac-quisition and Digital Signal Pro-cessing) offers over 150functions for displaying andanalysing waveforms, calculat-ing and prqsenting data withthe power and flexibility of aspreadsheet. Complex signalprocessing chains are created

in windows, allowing fullworksheets to be built up andstored quickly and easily. Thenew version adds the facility ofrunning external programswithin the DADiSP environ-ment.

Details from Adept ScientificMicro Systems Ltd 3 Letch-worth Business CentreAvenue One Letchworth Herts SG6 2HB England Telephone (0462) 683355.

RS232 testerComtest from TOOLRANGE is atime and trouble saving instru-ment for anyone who installs,repairs, or uses RS232 equip-ment. It needs no battery orother external power source, iseasy to use, and TOOLRANGEclaim that it is the most flexiblein -line communications testeravailable on the market today.

Details from TOOLRANGE Ltd Upton Road READINGRG3 4JA Telephone (0734)29446/22245.

1111 -LLo .,.7

30MPUTER NEWS COMPUTER NEWS

Honeywell IPC has expanded itsrange of IPC 620 programmablecontroller systems to includethe new powerful IPC 620.25and IPC 620-35 systems, aswell as the smaller low-cost IPC620-1011 and IPC 620-1511.The IPC 620-10 and 610.15have also been upgraded.

Real world control withVME I/O subsystemThe I/O subsystem from PSI ofCambridge offers the plantengineer a simple path to realworld control. It consists of anintelligent VME input-outputcontroller with a wide range ofbus -independent signal con-ditioning modules.A single 3U Eurocard provides32 digital I/O lines and 32analogue inputs. The system isvery easy to use and program.High-level commands can besent via the VME-bus to thecontroller, which is left to ex-

ecute them.The system can be used withany VME-bus. PSI VME basedsystems provide local intelli-gence for VME support disk,video, and keyboard, and also a68000 or 68010 CPU runningunder the OS -9 operatingsystem.

Further information from Cam-bridge Microprocessors Sys-tems Ltd BrookfieldBusiness Centre Twenty -pence Road Cottenham CAMBRIDGE CB4 4PS Tele-phone (0954) 51122.

Low-cost alternative toMotorola's MVME110The TVME 1612 single -boardmicrocomputer from TL In-dustries of Ohio is a low-costalternative to Motorola'sMVME110. Its one-off price isonly £670.

Manufactured in surface -mounttechnology, the board canoperate as a stand-alone con-troller in a single -processorVME-bus system, or with otherSBCs in a multi -processor en-vironment in applications suchas industrial control.

An advantage of the TVME 1612over the Motorola board is itscapability to supply the VME-

-bus with a 16 MHz clock whilethe microprocessor runs at10 MHz, eliminating the needfor a separate system controller.Further information fromUniversal Engineering andComputing Systems Ltd 5-UTower Street Newtown BIRMINGHAM B19 3UY.

First real-time imageprocessing chipsLSI Logic has unveiled a familyof image -processing ICs that,for the first time ever, allowstandard video images to beprocessed in real time. Thedevices are available as stan-dard products or as ASICmegacells and megafunctionsfor inclusion in more complexASIC designs.The family comprises fourchips that have four times theprocessing power of any com-peting digital signal processing

products currentlyavailable. These algorithmspecific products provide virtu-ally instantaneous data format-ting, filtering, noise removal,edge extraction, templatematching, and other operationsfor image processing and high -end DSP applications.

Data security in EuropeComputers and modern tele-communications equipmenthas become so ubiquitous thatthe potential for fraud and theftposes a serious threat to com-merce and industry. DataSecurity in Europe (#E894), a286 -page report just out fromFrost & Sullivan says thatbecause of this threat Euro-peans are trebling their spend-ing on countermeasures to $1.7billion a year by 1992.According to the report, datacrime figures show an increaseof 10% to 15% a year. Instruc-tions to a computer -drivenfinancial system to write andsend cheques for fictitionaltransactions is the most popularfraud in the financial system.The sums involved are large,witness the recent case whenPru-Bache narrowly managedto avoid a S6 million loss fromdata fraud.

Low-cost transputer-based moduleA 1 Mbyte transputer-basedmodule, Type TM2, is availablefrom Concurrent Techniques.Costing just £650, the TM2 canbe used as the basis for apowerful, compact parallel -processing system: up to eightTM2s cart be mounted on asingle Eurocard. This provides8 Mbyte and 80 MIPS from asystem that can be held in onehand.Applications for the TM2 in-clude robotics, image process-ing, PCB auto-routeing, finiteelement analysis, patternrecognition, and high-speeddistributed databases.Details from Concurrent Tech-niques 30 Baldslow Road HASTINGS TN34 2EYEngland Telephone (0424)714790.

EPROM/EEPROMprogrammerA new high -volume EPROM/EEPROM programmer, TypeXR16. is available from GP In-dustrial. It is designed for use inan industrial environment andsupports all the latest devices,up to 16 at a time.The programmer incorporatesultra -fast algorithms, such asQuick Pulse (Intel) and Flashrite(AMD), and is designed to sup-port 24, 28, 32, and 40 pinEPROMs and EEPROMs to oneMbit and beyond. A 512 x 8(4 Mbit) is supplied as standard.Further information fromGP Industrial Electronics Ltd Unit E Huxley Close Newnham Industrial Estate PLYMOUTH PL7 4J14 Tele-phone (0752) 342961.

tober 19: 11

HIGH CURRENT SWITCHINGREGULATOR IC SIMPLIFIES

SUPPLY DESIGNby Giuseppe Gattavari*,d

Containing a complete 2.5Aswitching regulator on a single chip,a power IC simplifies the design of

many power supply schemesand reduces cost.

While designers are attractedby the high efficiency ofswitching regulators, they areoften deterred by the com-plexity of circuits based on con-trollers such as the SG3524 anddiscrete power transistors.By integrating on a single chip acomplete switching regulatorcapable of delivering 2.5A at 5Vto 40V, the SGS L4960 High Cur-

rent Switching Regulator IC of-fers all the advantages of aswitching regulator yet is littlemore complex to use than a lin-ear regulator. A 2.5A/5V regu-lator can be built with oneL4960 and just eight compo-nents (Fig. 1) and higher outputvoltages are obtained by ad-ding two resistors. Moreover,the device includes current

limiting and thermal protectioncircuits, eliminating the need toadd extra circuitry.A further advantage is that theL4960's source -sink outputstage can switch in about 7Ons,allowing efficient operation (upto 90%) at switching fre-quencies of 100kHz. The IC is,in fact, tested dynamically at100kHz in production. Thanks to

1

.0-t1 !Or

SASITOOTtl

OSCILLATORCCso

Ald[CUP OUTPUT

STAGE

1.4960

*LIP5LCP

A0

1/1513/1 ALSRUIDGAM

A ACA

5 ISAEFERENCE

AEI;o50

L5,6

2_2 s.aC*,

S rs -

87176.1

Fig. 1. Containing a complete 2.5A switching regulator with current limiter and protection functions,the L4960 High Current Switching Regulator needs few external components.

the high frequency operationthe output LC filter componentscan be very small.The IC itself is assembled in thecompact Heptawatt 7 -leadpackage-both horizontal andvertical mounting versions areavailable-and requires only asmall heatsink. Consideringalso the few external compo-nents and small LC filter thecomplete application circuit isextremely compact (see photo).It can even be squeezed intothe corner of a system card.A versatile device, the L4960may be used in a number of dif-ferent ways.The most obvious is a basic DC -DC converter configurationwhere a 50/60Hz transformer,rectifier bridge and filter ca-pacitor feed the input of thedevice with an tmstabilized DCvoltage.

Multiple outputsAny number of devices may becombined to produce a mul-tiple output supply, permittinga building block approach tosupply design. In multi -chipsupplies it is desirable tosynchronize the switching fre-quencies and this can be doneby connecting the oscillatorpins in common to one RC net-work (Fig. 2).

EE

October 1987

2

105c

s-1224

L4960

L4960

87176.2

Fig. 2. So that several devicesmay be combined to producemodular multi -output supplies,the switching frequencies canbe synchronized by connectingthe oscillator pins together.

Very often low current auxiliaryoutputs such as +12V are re-quired. In this case it may benecessary to use severaldevices since an auxiliary out-put can be produced by addingan extra winding on the outputindustor as shown in Fig. 3. Inthis example the secondarywinding is not isolated-thebottom end is at 5V. This meansthat fewer turns are necessarythan if it were isolated, and loadregulation is improved.Circuits of this type have the ad-vantage of low cost and sim-plicity, and yield satisfactoryperformance as long as thepower drain on the auxiliaryoutput is no more than about20% of the power delivered bythe main output.Extending this principle,positive and negative auxiliaryoutputs can be obtained by ad-ding two windings, as shown inFig. 4. Since designers alwaysprefer to avoid inductors when-ever possible it should benoted that all of these circuitsrequire small toroids with asmall number of turns.

Pre -regulationIn all of the applications de-scribed above the L4960 sup-plies the load directly. Thedevice may also be used effec-tively as a pre -regulator forsupply schemes where on -cardlinear post regulators are used(Fig. 5). The advantage of thisapproach is that it enhancesregulation at the expense of ef-ficiency. Using an L4960 as thepre -regulator overcomes thepoor efficiency of post regu-lation without making thesupply excessively complex.The overall efficiency of this

Fig. 3. A low -current auxiliary output can be obtained by adding anextra winding on the output inductor. This technique is simple andinexpensive, yet works well provided that power drain on the auxili-ary output does not exceed 20% of the power delivered by themain output.

2 lrF

87176-4

Fig. 4. With two extra windings both positive and negative auxiliaryoutputs can be produced with just one device.

Fig. 5. An L4960 can be used as a pre -regulator in supplies whereon -card linear post regulator are employed.

scheme can be further in-creased by using new -gener-ation low drop linear regulatorslike the SGS L4941 for final regu-lation. These 5V/500mA regu-lators have a maximum dropoutvoltage of 650mA, allowing theuse of a lower intermediatevoltage.

Offline switchingsuppliesAnother important applicationis where the L4960 is used toregulate auxiliary outputs inhigh power supplies where themains transformer has been re-placed by an offline switching

Fig. 6. In a conventional offlineswitching supply, linear regu-lators are used to stabilize theauxiliary outputs. This solutionrequires a costly transformerand dissipation is a problem.

regulator to reduce size andweight.To understand the advantage ofusing switching regulator chipsin this application it isnecessary to examine thedrawbacIG of the conventionalcircuit, illustrated schematicallyin figure 6. In this example, afeedback circuit guarantees thenecessary precision for themain 5V output while conven-tional linear regulators stabilizethe other outputs.A major drawback of thissupply design is the cost of thetransformer. A separate sec-ondary is needed for each out-put and each must be opti-mized to obtain a low drop -outvoltage, otherwise power dissi-pation wil be excessive.The linear regulators used inthese supplies are either ICs(for currents up to 2-3A) ordiscrete circuits. Either way,power dissipation also be-comes a problem in overloadand short-circuit conditionssince the current limiters are ofthe constant -current type. It istherefore necessary to com-plicate the circuit further by ad-ding thermal protection circuitsor to use a large, and costly,heatsink.A final consideration concernsthe rectifier diodes betweenthe secondary windings (onefor each output voltage) and thefilter capacitors. With a linearpost regulator the input currentis always equal to the output

EE

October 198724

current so the diodes must bedimensioned accordingly.All of these problems areeliminated by using the L4960as a post regulator as shown inFig. 7. Note that for all of theauxiliary outputs only one sec-ondary is needed, simplifyingthe transformer. Cross regu-lation is no longer a problemand the power dissipated in thestage depends mainly on loadcurrent and is almost unaf-fected by dropout. Moreover,the diode on the secondary canbe smaller since the input cur-rent of a stepdown switchingregulator is always less than theoutput current.

Fig. 7. Using DC -DC convertercircuits in place of the linearregulators simplifies the trans-former and reduces dissipation.

Finally, short circuit protectionis provided for all of the auxili-ary outputs by the chip'sinternal current limiter andthermal protection circuit.

Giuseppe Gattavari is withSGS Microelettronica SpA

How it worksThe SGS L4960 is a monolithic stepdown switching regulatorproviding output voltages from 5.1V to 40V and delivering up to2.5A output current.At the heart of the device is a regulation loop consisting of asawtooth oscillator, error amplifier, comparator and source -sinkoutput stage. An error signal is produced by comparing the out-put voltage with a precise 5.1V on -chip reference which iszener-zap trimmed to ±2%. This error signal is then comparedwith the sawtooth signal to generate the fixed frequency pulse -width -modulated pulses which drive the output stage. Gain andfrequency stability of the loop are adjusted by an RC networkconnected to pin 3.When the loop is closed directly by connecting the supply out-put to the feedback input (pin 2) an output voltage of 5.1V is pro-duced. Higher output voltages are obtained by inserting avoltage divider in this feedback path.Output overcurrents at switch -on are prevented by the soft -startfunction. The error amplifier output is initially clamped by theexternal capacitor Css and allowed to rise, linearly, as this ca-pacitor is charged by a constant -current source.Output overload protection is provided in the form of a currentlimiter. The load current is sensed by an internal metal resistorconnected to a comparator. When the load current exceeds apreset threshold, this comparator sets a flip flop which disablesthe output stage and discharges the soft -start capacitor.A second comparator resets the flip flop when the voltageacross the soft start capacitor has fallen to 0.4V. The output stageis thus re -enabled and the output voltage rises under control ofthe soft -start network. If the overload condition is still present,the limiter will trigger again when the threshold current isreached. The average short-circuit current is limited to a safevalue by the dead time introduced in the soft -start network.The thermal overload circuit disables circuit operation whenthe junction temperature reaches about 150 :C and hashysteresis to prevent instability.

ELECTRONMICROSCOPYCOMES TO LIFE

by Dr Jitu Shah, H.H. Wills Physics Laboratory, University of Bristol

One important limitation of electron microscopes is that theconditions under which the specimen is examined make it

impracticable to view living matter. Results from a technique nowunder development are showing rapid progress in microscopy of

biological materials and are paving the way to observing thedynamics of life at high magnifications. Incidentally, it will alsoprovide industry with a powerful tool for inspection and fault

finding.

A desire to see structure, formsand morphology at micro-scopical scales is inherent tothe curiosity of mankind. Is wasthe driving force that led An-thony van Leeuwenhoek, aDutch clockrnaker, to devise acompound light microscope.Nowadays, of course, muchlarger magnifications can beobtained by electron micro-

scopes. Yet optical microscopystill has a powerful advantageover electron microscopy: itcan be performed on livingmatter without destroying it.It is interesting to note that in1926, when the US physicist LeoSzilard suggested to the Britishengineer Dennis Gabor that anelectron microscope might bemade by assembling electron

lenses, Gabor (later the inventorof the hologram and winner of aNobel prize in physics) rejectedthe idea and pointed out that liv-ing specimens cannot beplaced in a vacuum, which isessential for electron beam op-tics, and that energy in thefocused electron beam wouldburn and destroy anythingplaced under it.

In the event, the first suchmicroscope was built by theGerman scientists Max Knolland Ernst Ruska in 1931. Ad-vances since then in manybranches of materials science,biology and medicine can beattributed to the use of electronmicroscopy. This has been dulyacknowledged by the fact thatErnst Ruska shared a 1986

EE

October 1987

Scanning electronmicroscope column

To vacuumpump

To waterreservoir

To vacuum -4-pump

To videoamplifier

t. Electron beam

Intermediate chamber

Specimen chamber

Schematic diagram of the apparatus used for MEATSEM.

Nobel prize in physics, so it isappropriate now to review howfar electron microscopy forbiological and other difficultmaterials has progressed.With a modern, commerciallyavailable transmission electronmicroscope (the type devel-oped by Ruska) we can visu-alise features and structures ofonly a few tens of angstrOms.However, such an instrumentrequires the specimen to bethin, because an image is ob-tained by passing electronsthrough it. This means that sur-face features of a thick, three-dimensional object cannot beexamined very well. Addition-ally, because the specimenshave to be very thin, it is ex-tremely laborious to obtainthree-dimensional information.These disadvantages are over-come by the scanning electronmicroscope, a type of instru-ment first built by the Germanphysicist Manfred von Ardennein 1938.

Depth of focusThe first commercial scanningelectron microscope was madeavailable in 1965 by CambridgeInstruments, a British firm nearCambridge. In this kind ofmicroscope an extremely

small, focused spot of electronsis made to fall on the surface ofa specimen and scan across itin a 'raster', just as in an or-dinary television tube. Theelectrons interact with thespecimen and release second-ary electrons from near the sur-face. (Some of the primary,incident electrons are ab-sorbed within the specimenwhile some are bounced backout of the surface; more aboutthis back -scattering later.) Emit-ted secondary electrons yieldinformation about the surfacetopography.In a conventional scanningelectron microscope these sec-ondary electrons are collected,point by point, and used tobuild a picture. Deeper surfacefeatures of thick specimens canbe imaged in a scanning elec-tron microscope because thedepth of focus is much geaterthan that in an optical micro-scope, so the technique gives amuch more vivid impression ofthree -dimensionality. It displaysmorphological and topologicalfeatures at much higher mag-nifications than in an opticalmicroscope. Because the in-strument is relativily easy to useand can be combined withother analytical techniques, it

has become enormously popu-lar. Magnifications available

with modern instruments areonly slightly less than thosepossible in a transmission elec-tron microscope.When it comes to viewing liv-ing matter, scanning electronmicroscopy has the sameserious drawbacks as thosepointed out by Dennis Gabor.Therefore we must be able tokeep specimens in a micro-scope in a fully hydrated state,without loss of water. That is tosay, they must be kept as nearas possible to a living state.In any electron microscope, awell -focused beam of high-energy electrons, necessary forimaging, has to be producedand kept in a high vacuum. Itcannot travel long distances in ahigh-pressure gaseous environ-ment without being scatteredby gas atoms or molecules andlosing its energy, and a badlyscattered beam cannot renderhigh resolution. This is anobstacle to electron mi-croscopy of biological materialin its natural, hydrated state.For these reasons specimensare, conventionally, deliberatelydried out and made stable forviewing by using proceduressuch as chemical fixation,dehydration and fluid replace-ment. Additionally, for scanningelectron microscopy, dehy-drated specimens, which are

generally poorly conducting,are coated with a thin conduct-ing layer of gold or of an alloy ofgold and palladium to avoid abuild-up of charge, for detailedfeatures on charged surfacescannot be imaged well. Butthese techniques cause adrastic change in interfacialtension forces, which in turncauses delicate biologicalstructures to become distortedand even to collapse. In spite ofthe development of specialtechniques for preparingspecimens it has not been poss-ible to eliminate damage com-pletely.Loss of water in a vacuum canbe avoided by freezing thespecimen and keeping it at alow temperature, at whichsaturated water pressure is verysmall. In so-called cryo scan-ning electron microscopy,specimens are frozen, coatedwith metal and transferred intothe scanning microscope,where they are viewed at a lowtemperature. However, frozenspecimens are not free fromdamage which takes placethrough anomalous expansionof water as it changes into icecrystals. Obviously the cryotechnique, even if it were madefree from specimen damage,could not be used to view livingmatter.

EE

October 198726

Two regionsAnother approach for solvingthe problem of loss of wateris called moist environmentambient temperature scanningelectron microscopy(MEATSEM). This relies oncompartmentalisation of amicroscope into two regions:the first is a high -vacuum regionfor electron beam productionand electron lense optics; thesecond is a high-pressureregion at room temperature, tosurround the specimen andprevent it from losing fluid andgaseous constituents. (If aspecimen is kept at saturatedvapour pressure of water or 100per cent humidity it will remainwet, just like clothes hangingon a washing line on a humidday.) Complete compartment-alisation can be achieved byusing a window that is trans-parant to electrons but at thesame time tough enough tomaintain a high difference ofpressure between the two com-partments. This approach hasthe drawback that windowmaterials scatter the electronbeam badly. To keep scatteringdown to feasible levels the win-dow has to be extremely thin,which means it is extremelyfragile. Reliable windows withan acceptable loss of resolutionare difficult to make.We have adopted an alternativemethod of open -windowMEATSEM here at Bristol. Thefocused electron beam passesfrom the microscope to thespecimen chamber via smallapertures. as shown in the firstdiagram. Leakage of gases fromthe high-pressure region to themicroscope column is kept to aminimum by introducing abuffer space, or intermediatechamber, between thespecimen region and the elec-tron beam column. The in-termediate chamber isbounded by two walls contain-ing concentric limiting aper-

-so

Normalisation(Cu - C) zerobias -1

Grid image at -1 x 10' Vm'bias

-50 -40 -30

-16

12

8

4

0

10kV

Grid image at +1 x Vm-'bias

-20 -10 0 10 20

BIAS FIELD STRENGTH Ix 103 Vm )

C

Cu

I

I30 40 9360

Variation of 'normalised' specimen current with field bias strength for 10 -kV accelerated primaryelectrons. Normalisation is on the basis that the difference between the specimen current from copperand carbon at zero field strength is unity.

tures in the planes normal to theelectron beam, and it ispumped continuously so thatthe pressure gradients can bemaintained while the micro-scope is in use. Water lostthrough the window is re-placed by a continuous injec-tion off water vapour in thevicinity of the specimen. Tokeep damage due to water lossfrom the specimen to a mini-mum, a sponge is introduced tothe specimen chamber. Thesurface area of the sponge ismuch larger than that of thespecimen, so the proportion ofthe water lost from thespecimen to the total loss ofwater is very small.Scattering of the electron beamin this arrangement dependslargely upon the pressure in thespecimen compartment andhow far the electron beamtravels through the highpressure to reach the

specimen. Pressure in thespecimen chamber is kept atthe saturated water vapourpressure, at near to room tem-perature. With careful design ofthe apparatus the scattering ofthe primary beam can be keptdown to give reasonable resol-ution. We have used this open -window MEATSEM with somesuccess: it is now possible to in-sert a fully hydrated specimeninto a scanning electronmicroscope and keep ithydrated for a long time. Never-theless. preventing desiccationof a specimen in this way posesanother problem.

Additional electronsForming an image under thisconditions presents formidabledifficulties. The conventionaltechnique of constructing animage by secondary emittedelectrons does not work

because secondary electrons,primary electrons and back -scattered electrons ionise wateror gas molecules close to thespecimen and produce ad-ditional electrons. These elec-trons, which do not carry anyinformation about the specimensurface, have a similar energyrange to that of the secondaryelectrons emitted from thespecimen, so they cannot beseparated easily from thesecundary electrons releasedfrom the specimen surface.Without such separation, thereis a severe deterioration of thesecondary emitted image.Back -scattered electrons(deflected primary electronsfrom beneath the specimen)also carry image information.Because they are scatteredfrom a larger volume ofspecimen, the resolutionachievable by their use is not asgood as that obtainable by

Stomata, or breathing pores, viewed by open -window MEATSEM at successively higher magnifications, which eventually reveal a tubularstructure with a slit within a stoma.

EE

October 1987

Left: view of part of a circuit on a semiconductor wafer showing charging effects; 'spread' in the darker area is due to charging.Right: A view of the same circuit after charge neutralisation.

using secondary electrons.Further deterioration in the res-olution is also likely becausethe low -energy of back -scat-tered electrons means that theycannot be separated easily fromspurious electrons.Interaction of the primary elec-tron beam with the specimencreates a charge which, in turn,generates a minute current inthe specimen. The point-to-point variation of this currentwith scanning of the beam canbe made use of for image gen-eration. With a wet specimenthe current can be collectedwithout any metal coating. Aspecimen -current image is alsosusceptible to deteriorationthrough ambient ionisation. Ourresearch has shown that it ispossible to resharpen the im-age in a way that I shall now de-scribe.We have incorporated an ad-ditional annular electrode inthe specimen chamber so that asubstantial electric field can beproduced at the surface of thespecimen. The field has a con-siderable effect on the speci-men current, shown in thesecond illustration. The imagesare of copper grid bars on acarbon surface, and the curvesrepresent variations of speci-men current with the strengthof electric field from copperand carbon. It is thought thatthe electric field helps to con-duct the excess charged car-riers, produced by the inter-action of primary, back -scat-tered and secondary electrons,

through the gases, which en-hances the contrast in thespecimen -current image. Ap-plication of the field changesthe magnitude of the specimencurrent rapidly at first and thenmore slowly as one or otherplateau in the curve is reached.The image quality and contrastis re-established with themagnitude of the field applied.It is also possible to invert theimage contrast by changing thedirection of the imposed field.The curves shown for copperand carbon indicate that thecontributions to the current byboth the back -scattered elec-trons and the secondary emit-ted electrons are recovered to agreat extent in the plateauregions. So, once the specimencurrent reaches a plateau, thecontrast, sharpness and resol-ution of the specimen -currentimage of an object under highpressure are substantiallyrecovered. The image is com-parable in quality to the con-ventional, secondary emissiveimage of a similar object in ahigh vacuum.A series of pictures in the thirdillustration shows recovered im-ages of stomata of a fullyhydrated leaf, at roughly 16 °C,at various magnifications.Stomata are breathing pores ofa leaf, which automaticallyclose and open to regulate ex-change of water vapour be-tween the leaf and the air. Theyare therefore suitable speci-mens to study by MEATSEM ona fully hydrated leaf.

Fully hydrated internal tissuecells of animals can be imaged,too. The resolution obtained sofar is limited by factors notdirectly related to the principleof the technique, while difficult-ies stem from the fact that thecurrent from a typical uncoated'wet' biological specimen issmaller.Results indicate that we maywell see rapid progress in scan-ning electron microscopy ofhydrated biological materials.In turn this will open up meansof realistically assessingdeterioration from othercauses, such as radiationdamage due to incident elec-trons and heat produced by theinteraction of electrons with aliving specimen. Optimistically,we may expect other advancessuch as low -voltage scanningelectron microscopy combinedwith MEATSEM, which maywell enable us to view live mat-ter without inevitably killing thespecimen. This will not onlyfulfil a long standing dream ofmankind but also provide a toolfor observing the dynamics oflife at high magnifications.MEATSEM has led to a solutionof another long-standing prob-lem in scanning electronmicroscopy. I have alreadymentioned that insulating,semiconducting and poorlyconducting materials are diffi-cult to image, unless coated, ina scanning electron beam in-strument because of chargebuild-up on the surface of thespecimen. It alters the trajec-

tories of primary and second-ary (emitted) electrons and theprocess of emission of second-ary electrons; this grosslydistorts the image and is alsoaccompanied by loss of detailsand resolution. Charging canalso bring about electricbreakdown of the material,which is particularly serious inexamining semiconductorchips containing circuits andactive electronic devices.With certain modifications ofthe open -window MEATSEM, acharge neutralisation mechan-ism can be employed to reduceor eliminate charge build-up ona surface. The final illustrationshows before -and -after imagesof a circuit on a semiconductorwafer. The improvement wasachieved by charge neutralis-ation. Potentially, the techniqueis a powerful tool for inspectionand fault detection, and pro-mises to have other industrialuses. Cambridge Instruments,who built the first scanningelectron microscope, may wellbe the first company to makethe MEATSEM and its associ-ated techniques available com-mercially.

EE

October 198728

FILTERS: THEORY & PRACTICE 3by A.B. Bradshaw

Television, radar, data transmission, and other techniquesdeveloped during the 1940s and 1950s showed up the

limitations of the image parameter theory. The higher precisionand more exact characteristics required of filters from then on

caused the image parameter theory to give way to the modernnetwork theory that uses synthesis techniques and digital

computers.

36

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stop bud anemia:Labe.

transiason sodaappoodustseas

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VoSsiSOs

The underlying principle of thenetwork theory is to synthesizethe filter from a knowledge ofits voltage transfer function(voltage vs frequency charac-teristic). This is an essentiallymathematical approach usingthe ratio of certain types ofpolynomials. Known as approxi-mation theory, it is a verypowerful technique. Usingthese methods, three of the ap-proximations yield familiartransfer functions. Togetherwith the ideal brick wallresponse, they are shown inFig. 36.The development of the digitalcomputer greatly aided in theevolution of the polynomialcoefficients. This enables filterdesign tables to be producedfrom suitable computer pro-grams.The use of such tables, coupledwith a step-by-step design pro-cedure, enables the productionof superb filters to the Butter-worth, Chebyshev, and ellipticfunction approximations.The tables refer to normalizedlow-pass and high-pass sec-tions. "Normalized" means thatthe circuit values all refer to anetwork impedance of 1 Q at anangular frequency, (I), of1 radian. By using standardmultipliers, it is possible totranslate the filter impedance tothe desired value. Another setof standard multipliers enablesthe translation of the shape ofthe response to the requiredfrequency. These two oper-ations are carried out simul-taneously and are referred to asimpedance/frequencyscaling.The basic structures given inthe tables can be converted tohigh pass and a networktransformation enables trans-lation into band-pass structures.These new structures are then

scaled to the desired im-pedance and frequency to givepractical values for the com-ponents.Once a set of filter designtables is available and thedesigner has familiarizedhimself with their main proper-ties, it is easy to produce high -quality filter designs withoutthe need to know anythingabout the coefficients of realrational functions or Hurwitzpolynomials.

Elliptic function tablesThe elliptic function tables arechosen as these give the best

results for a given number ofcomponents in the design (Ref.1).

Each table refers to a specificnetwork. Each set of figures isgiven for a range of stop bandattenuations (usually in 5 dBsteps for the shorter network),and for a given pass -band rip-ple in dB. The figures in thecolumns are the actual com-ponent values referring to03=1 radian and Z=1.How the tables relate to the net-work is shown in Fig. 37 andTable 1. This table shows onlytwo lines of the general tablewith 1 dB pass -band ripples.Table 2 shows two lines of the

Table 1

Ws As Ci C2 U W2 C3

I I I I I I I

I I I I I 1 I

I I I I I I I

I I I I I I I

2.048 35 1.852 0.214 0.865 2.324 1.8522.418 40 1.910 0.145 0.905 2.762 1.19C

Table 2

Ws As Ca C2 I-2 W2 C3

I I I I I I I

I I I I I I I

I I I I I I I

I I I I I I I

2.921 35 0.958 0.0837 1.057 3.362 0.9583.542 40 0.988 0.0570 1.081 4.027 0.988

29 EE

October 1987

Table 3Ws As CI C2 L2 W2 C3 C4 LA W4 C5

I I I I I I I I I I I

I I I I I I I I I I I

I I I I I I I I I I I

I I I I I I I I I I I

1.145 35 1.783 0.174 0.827 1.597 1.978 1.487 0.488 1.174 1.2761.217 40 1.861 0.372 0.873 1.755 2.142 1.107 0.578 1.250 1.4271.245 45 1.923 0.293 0.947 1.898 2.296 0.848 0.684 1.313 1.5531.407 50 1.933 0.223 0.963 2.158 2.392 0.626 0.750 1.459 1.6351.528 55 1.976 0.178 0.986 2.387 2.519 0.487 0.811 1.591 1.7321.674 60 2.007 0.141 1.003 2.660 2.620 0.380 0.862 1.747 1.807

general table with 0.1 dB pass -band ripples.In the worked examples givenlater in this article, the longerlow-pass network of Fig. 38 willbe used. For this longer net-work, figures are given inTable 3 for stop -band attenu-ations from 35 dB to 60 dB with1 dB pass -band ripples.In the tables,ws is the frequency at whichthe specific attenuation begins;A5 is the specified stop -band at-tenuation;Cl-05 are the values of thecapacitors in farad;1,2 and L4 are the values of in-ductors in henry;Cat and C4/4 are the angular fre-quencies at infinite attenuation.The values of the capacitorsand inductors are very largebecause the network refers to1 o at 1 radian: they will be-come more practical during theimpedance/frequency scaling.Note that the pass -band edge isthe ripple limit and not the-3 dB point.

Low-pass filter forSSB receptionWith reference to the last threelines in Table 3, if the pass -bandedge is defined at 2.2 kHz(-1 dB), the following fre-quencies would obtain at the at-tenuations stated:

50 dB: 1.407 x 2.2=3.0954 kHz55 dB: 1.528 x 2.2=3.3616 kHz60 dB: 1.674 x 2.2=2.6828 kHz

If the pass -band edge were

defined at 2.7 kHz (-1 dB), thefrequencies at the given at-tenuations would become:

50 dB: 1.407 x 2.7 =3.7989 kHz55 dB: 1.528 x 2.7=4.1256 kHz60 dB: 1.674 x 2.7=4.5198 kHz

As regards the filter im-pedance, generally speaking,the higher this is, the larger theinductances become, and thesmaller the capacitances. Atrelatively high impedances, thecapacitors can be matchedmore easily by using 1% silvermica types. The large induct-ances may be avoided by elec-tronic simulation, of whichmore later.Using the last line of Table 3and deciding on a filter im-pedance of 1 kQ, and a pass -band edge of 2.3 kHz, the twoinductances can be calculatedwith inductance multiplier V.This multiplier is determinedby

L._(dekgr. bapedance)(ir.4,:xtarze from mEel2 .0,,,. -edge frequency)

The required inductancevalues, /f; and L are thencalculated as follows:

ICI'xM H=59.405 mHx2_3x10.

L:- x()-56:2 -O_Ce9E' 48 H.51E4-8 mil2:x2.3,00.

The capacitance multiplier, C',is determined from:

(capacm:ace Er= tah:e)(design 6sspedar.ceX2c (bard edgefrecrcenci)f

The capacitance values cannow be calculated:

C:= 2.037 -111.8799 rF103x2xx2.3x:6'

Ll= 0141 -175033 nF10.)atx23xI0P

Similarly,

C13.181.2982 nF

C<=26.295 nF

Cs =125.040 nF

Since these capacitance valuesare rather large, it is more prac-tical to decide on an im-pedance of 10 kQ, which makesthe inductances 10 times larger,and the capacitances 10 timessmaller. This will result in a10 kQ filter with the same at-tenuation vs frequency shape.as shown in Fig. 39. This figureshows the complete low-passfilter and its frequencyresponse.

Band-pass filter forCW receptionThe desired frequencyresponse curve of the band-pass filter is shown in Fig. 40.Frequencies f and 12 are theband edges at -1 dB (in thiscase); 13 and Is are the fre-

quencies about fo at which Asoccurs; and fo is the centre ofthe pass band. Note thatfi= fif2=f3f4 and that A /A-2. -1 =First, a value is chosen for fo.Then, from the tables, 14 for agiven As is determined, afterwhich 13 can be calculated.Subtracting /3 from 14 gives A2.Then, since ws is given in therelevant line of the table, Ai canbe calculated.The values of the following arenow known: el; Az; fo; 13; and fs.Now, since AI =12 -fl,

AI =f2-(filfz)

which is a quadrature in 12, sothat

46112=il-fl

This is a simple quadratic equa-tion, whose positive root is

f2=(A1 +1 Ai ÷4fo2)12

A2=f4-f3=

=e;sfo--fo/cos

Since A2/A, =

A14.13=a/S16-10/COS

from which

(fa-A1),..cs=fo/ws

and

[37]

tos=1fol(fo-A1) [381

This establishes ws and the lineof the table with which todesign the filter.Taking fa = 850 Hz (the mostpopular CW-morse code -tone), and a bandwidthAt =300 Hz, gives (from Eq. 38):

(05=1850/(850-300)=1.243

The nearest value to this inTable 3 is 1.245, and this wouldgive a stop -band attenuation of45 dB. Having established therelevant line in Table 3, the tran-

EE

October 198730

sition frequencies can becalculated. From Eq. 37:

12 = (300 +1 3002 + 4 x 8502)/2 ==1013 Hz

and

A=1013-300=713 Hz

f3=W sfo= 1.245 x 850= 1058 Hz

13.10/ ws=850/1.245=682 Hz

From these results, theresponse characteristic can bedetermined and this is shown inFig. 41. The actual filter diagramis shown in Fig. 42. If a morerectangular shape or a greaterstop -band attenuation at thisbandwidth is required, a morecomplex network needs to bedesigned.

42

This may be done by convert-ing the circuit of Fig. 42 to thatof Fig. 43. In this, eachcapacitance and inductance ofFig. 42 is resonated by placing.

the opposite reciprocal reac-tance in series or parallel with itas appropriate.The two rather untidy middlesections are then transformedto more simple ones by a step-by-step transforniation asshown in Fig. 44. For thistransformation, let

x=L/Ka=1+1/2xi3=1(02-1)y= a + /3La =1/(y+ 1)

With the aid of these identitiesand a hand-held calculator, thefirst mid -section of Fig. 43 iscomputed:

x=LIK=0.947/(1/0.293)=0.947 x 0.293 = 0.277471

C7 = 1+1/2x= 2.80199

11=1 (C12-1)= 2.61746

y=a+p=5.41945

Lo=1/(y + 1)= 0.155776

The values of the componentsin Fig. 44 can now becalculated:

KLo =(l/0.293) x 0.155776 ==0.531658

y/fLo =5.41945 x (1/0.293)x 0.155776=2.88129

1/yKL0 = 0.347065

1/Kbo =1.88090

44

KL0-rr,"--YKL°

1 tr a nslocms ---

-IFKLo

-

VIL3414.1

This gives a First mid -section asshown in Fig. 45.Treating the second mid-section of Fig. 43 in the sameway, gives

450..531658 2.88129

--II- I-0.347 065 1.88090

est:344s

x= 0.580032o =1.86202/3=1.570708y= 3.432728L0=0.2255947

from which

KLo=0.266031

yKLo=0.9132137

Ilyno=1.0950339

11Kto=3.7589604

This gives the second mid-section as shown in Fig. 46.

460266031

10--0.9132137

-II- -II-1.0450339 3.7589504

The complete filter is shown inFig. 47. For a 10 kg networkwith a centre frequency,L=850 Hz, the inductances andcapacitances can be calculatedfrom:

L=ZI2rEfo x (L in network)

and

C=(C in network)/2da

The following values are ob-tained:

L1=97.369 mHL2=99.548 mHL3 = 539.495 mHLl = 81.550 mHL5 = 49.8119 mHL6 = 170.991 mH177 = 120.567 mH

and

C1=0.36006 14FC2 = 0.06498 pFC3 = 0.35218 pFC4=0.42990 IXCs =0.20503 pFC6 = 0.70383 pFC7 = 0.29078 pF

Since these capacitor valuesare too large for practical pur-poses, it is propitious to in-crease the filter impedance to10 k to make the values of thecapacitances 10 times smallerand those of the inductances 10times larger. This results in thefinal design shown in Fig. 48.

The Positive Im-pedance Converter(PIC)As stated earlier, inductancescan be electronically simulatedand this is done by the use of

EE

October 1987

positive impedance converters.The theory of these devices isdiscussed on page 54.When the output port of a PIC isterminated by a resistance, theinput port becomes an inductorwith a very high Q. In Fig. 49

RI =270R 1%R2=5k6 I%R3=10 k 1%C=10 nF mica 1%

(2 x 5000 pF in parallel)IC =MC1458 (supply= ±12 V)

49C

ent3-1.1

At the input port,

Lin =KR0

where K=CR,R31R2

[391

With the MC1458, the value ofK=5.17155 x10-6. The deviationfrom the ideal K is due toopamp approximations. Withthis value of K,

Lin= 5.17155 x IVRo

Inductances in the filters dis-cussed in this article aresimulated by PICs as shown inFig. 50. In Fig. 50 (c), LI issimulated by PICI +PIC2Rol,while In is simulated byPIC2R02. The PIC can betrimmed to have a K value of5.17155 x10-' by adjustment of R3in Fig. 49.When the inductances are re-placed by PICs, the low-passfilter of Fig. 39 becomes asshown in Fig. 51, while theband-pass filter of Fig. 48 is

50-II

-- PIC

Grounded colt simulation

1+

y Ro

PICi

=NI

R.PIC2

Vp

Balanced cal simulation

L2

ItpPIC1

RotPIC2

0 Rot

Grounded / balanced coils simulationE/14341-5.3

51Ua

PICi

C17-C2

Cr

TM,"

PIC21, 1, ,

PIC3

Rot

C.3MIM

11313:p

CI

f714.1.14.51

LPF

tat

52Rot Rot

Plct

± If.-G.Ic 2.1.21

Ro3 Roy

ii

1. C

PIC2

TIECCEc

PIC3

CIL

Ros Ro6 R0.7 BPF

PICA

1.p

tak

171/3111-52

transformed into that of Fig. 52.It is important to match thePICs. The value of each Ro iscalculated with the aid of Eq. 39(Lio =KR°, whence Ro=IcnIK).Thus, in Fig. 51:

Rol =10qt/5.17155==(106/5.17155X694/103=134 k

R02= -(106/5.17155X596.5/103)==115 k

In the same manner, the valuesof Rot to Rol in Fig. 52 arefound; their values are:

Roi=188 kRo2=192 kR03=1.043 M.Ro.; =157 kRos=96 kRo6 =330 kRol =233 k

End

Reference:On the Design of Filters bySynthesis; IRE Trans: CircuitTheory, Vol. CT -5 1958,pp 284-328, by R. Saal andE. Ulbrich

More links to ChannelIslandsA recent Anglo-French agree-ment aims to strengthen com-munications between theChannel Islands and the Britishmainland. The agreement pro-vides for a new route bymicrowave from Dover toBoulogne, cross Normandy bymicrowave and cable toBarneville, and then by

microwave to Jersey, where itwill link into the ChannelIslands' own microwave system.At present, the Channel Islandsare linked to the UK by threecables, which have a total ca-pacity equivalent to 3,240 simul-taneous telephone callg, and bystandby microwave radio be-tween the Isle of Wight andAlderney, which is able to carry960 calls simultaneously.

The 120 km long microwavelink is affected by weather con-ditions, while the existingcables are liable to damage byshipping.A new submarine cable with 12optical fibres is planned to bebrought into service by early1989. This, will be digital, in-itially operating at 140 Mbit/swith two fibre pairs equippedto provide capacity for around

4,000 simultaneous calls.The new route across Francewill also operate at 140 Mbit/sand have a capacity of nearly2,000 simultaneous calls. Whenit comes into service by the endof November next year. it willprovide greater diversity andsecurity of communications.

EE

October 1987

IEC-CENTRONICS INTERFACEby K Fietta

The use of an IEC or IEEE bus for driving a Centronics compatibleperipheral device calls for a special interface circuit to ensure the

correct timing of handshaking signals NRFD and NDAC.

The IEC bus is mainly used onminicomputers and main-frames, but is currently findingits way in some home microsalso. In essence, the IEC bus isa parallel input/output port thatcan be adapted for use as aCentronics interface. The inter-face proposed here is a rela-tively simple type whichenables driving virtually anyCentronics compatible printerfrom an IEEE 488 bus. TheIEC/IEEE 488 and Centronicsinterfaces have a number oftechnical features in common,and may be considered virtu-ally identical when usedunidirectionally.

In 1977, the International Elec-trotechnical Commission (IEC)published the document Stan-dard interface system for pro-grammable measuring equip-ment. This was the technicalreference for the IEC interface,which enables controlling awide range of measuringequipment with the aid of acentral computer. The standar-dization of the interface waswelcomed as a great helptowards the development of thecomputer -controlled test site.

The IEC interface was not anentirely new concept, however.In April 1975, the American Na-tional Standard Institute (ANSI)had already documented theIEEE 488 interface standard forsimilar purposes. Interestingly,the proposals of both the IECand the ANSI concerning an ad-dressable interface were basedon Hewlett Packard's system,which had been in use since1965. Today, the IEC bus is usedmostly in Europe, and the IEEE488 bus in the United States.Apart from the connectorsystem used-IEC 25 -way; IEEE488 24-way-these standardsare very similar. The term GPIB(general purpose interface bus)is often used to refer to the IECand IEEE 488 interfaces simul-taneously. The use of a 24 -wayconnector system was ac-cepted for the IEC bus also inview of the widespread use of25 -way (D) connectors for RS232based equipment. In the re-mainder of this article, theterms IEC bus, IEEE 488 bus,and GPIB bus will consideredsynonymous for practicalpurposes.In spite of the strict standardsfor its implementation, the IEC

1

010 5

010 6DIO 7

DIO 8

IEC connector

DIO - 1

DIO -2

1310 -3

DIO -4

REN

E01

DAV

NRFD

NDAC

IFC

SRO

ATN

shield

87045 - I

bus still leaves room for certainadaptations that may be re-quired to solve compatibilityproblems. In practice, thismeans that equipment control-led via the IEC interface neednot recognize all specifiedfunctions. Contrary to the Cen-tronics interface, which is virtu-ally always used to drive asingle peripheral (usually aprinter), the IEC bus is by defi-nition tailored to connectseveral devices in a network.

The IEC busThe IEC standard defines 16signal and 8 ground lines. Eachdevice connected to the busshould recognize at least 1 ofthe following 3 functionalmodes:LISTENER: addressed in thismode, the device reads the datareceived via the interface.Examples include printers. dis-play units, and programmablesignal sources.TALKER: addressed in thismode, the device sends data viathe interface. Examples includea paper tape reader and a

remote sensor system. The IECbus can only work with I activeTALKER at a time.

CONTROLLER: addressed in,or set to, this mode, the deviceassigns the LISTENER orTALKER function to otherdevices. The CONTROLLER isusually a (mini or micro) com-puter with an IEC interface. TheIEC bus can work with only 1active CONTROLLER at a time.

The logic levels on the IEC buslines are based on the defini-tions for TTL circuits:0.00 V to 0.80 V: logic "1" level;low; active; true; valid.0.81 V to 2.00 V: not defined.2.01 V to 5.25 V: logic "0" level;high; inactive; false; invalid.Note that the logic levels "1"and "0" are inverted withrespect to the electrical highand low levels. The negationbars commonly put over logicsignal names are not used in thefollowing discussion to avoidconfusion arising from the con-nection of a system based onpositive logic (Centronics) toone based on negative logic(IEC). Voltages in the abovementioned non -defined range

2

0102

0104

DAY

h0AC

SRO

S7NELD

0101

0103

E01

liAFD

IFC

ATN

femaleIEEE 488 connector

II

II

II

II

1411

113131

ENOS

0107

0106

REN

MOS

GOD 6

GM 7

GODS

WC 9

011010

G140 11

LOGICG/10

E7:15 - 2

Fig. 1 The 25 -way IEC connector. Fig. 2 The 24 -way IEEE 488 connector.

EE

October 1987

may only exist during logiclevel transitions. The pinningand signal denotation of theconnectors are shown in Figs. 1and 2. The 16 signals can befunctionally divided into 8

datalines, 3 handshake lines,and 5 command lines, as shownin Fig. 3.Datalines D101...D108 incl. areused for sending and receivingbytes of which the least signifi-cant bit is carried by DIOL Thedatalines also carry status infor-mation of the devices connec-ted to the bus. Signal ATNallows a distinction to be madebetween 2 types of information:ATN="0": data transmissionATN="1": interface -specific in-formationThe control (management) bususes the following 5 lines:IFC (interface clear): the CON-TROLT,FR initializes all devicesconnected to the IEC bus. Thisline is activated immediatelyafter power -up.ATN (attention): indicates thepresence of data or status infor-mation (see above).REN: (remote enable): remoteselection of the functionalmode of devices connected tothe bus. Usually, this line is per-manently active. In the inactivestate it enables manual modeselection of a device.EOI (end or identify): when theATN line is active, the CON-TROLLER uses the EOI signal toidentify a bus -connecteddevice. A TALKER uses EOI asthe "end of transmission"marker (ATN= "1"; EOI = "0").SRQ (service request): devicescan request communicationwith the CONTROLLER, whichinterrupts its current program toexecute the servicing program.

The following signals on thehandshaking bus accompany adataword on the databus:DAV (data available): by ac-tivating this line, the sendingdevice indicates that thedataword on the bus is stableand valid.NRFD (not ready for data): thisline is activated when a bus -connected device is not readyto receive data (low = notready).NDAC (no data accepted): thisline is activated when a bus -connected device hat not (yet)read the dataword from the in-terface (low = not accepted).

The order in which the hand-shaking signals are active dur-

ing the transmission of data isshown in Fig. 4.(1). Initialization of the DAV

signal by the source.(2). When a device is ready to

process a new dataword, itswitches its NRFD output to thehigh impedance state. NRFDgoes high only when alldevices are ready.(3). A new dataword can be

sent, and DAV indicates the

presence of valid data (4).

Devices activate NRFD (5) tosignal inability to accept newdata while the previousdataword is being loaded (6).All devices have an individualNDAC line in view of thespecific data loading and pro-cessing speed. When alldevices have accepted thedataword, all NDAC lines form ahigh impedance, and the signal

3

device Ie.g. mkt ocomptter

TaLtListenControl

desice IIe -g. sensor unit

TadkLsten

device IIIe.g. Pinter

de -4:e IVe.g. ta;.e- reader

Tea

corrtrot bus(5 Ernes)

- - synctucr:cialien bus(3 rues)

data Ws(I3 fines)

87045.3

eiot_osat

NDAC, DAV, NRFD

IFC, API. SROREN, E01

Fig. 3 Basic structure of the IEEE 488 bus, which supports up to15 devices.

4DIO 1...8

DAV

intetedfre

1

NRFD* aril. . .

(Tr,NDAC* WI'log

O

2-4 etta-fle

Fig. 4 Essentials of the handshaking procedure used in an IECinterface.

goes high. The sending devicewaits for all NRFD lines to revertto the inactive state, whichmeans that all devices have pro-cessed the previously loadeddataword. It then de -activatesthe DAV line (= false) (7) andawaits state (8) (NRFD = false).The handshaking cycle is thencomplete.

Functional aspects ofthe IEC interfaceEquipment fitted with an IECinterface should have the fol-lowing functions:1. Source Handshake (SH):This function ensures the cor-rect placing of dataword ontothe bus, controls the DAV linewhile monitoring the NRFD andNDAC lines, and is used byTALKERS and CONTROLI,FRsfor sending data and status in-formation, respectively.

2. Acceptor Handshake (AH):This receiver function fordatawords on the bus controlsthe NRFD and NDAC lineswhile monitoring the DAV line.The start of a transmission canbe blocked, and the enddelayed. with the aid of NRFDand NDAC, respectively.

3. Talker (T):This function entails sendingdata to one or more LISTENERS.The CONTROLLER selects thisfunction by means of a 1 -byteaddress in the device.

4. Listener (L):This function entails receivingdata from the CONTROLLER ora TALKER. The CONTROLLERselects this function by meansof a 1 -byte address in thedevice.

5. Service Request (SR):This function controls the SRQline. The CONTROLLER is toidentify the SR source from thedevices connected to the bus.

6. Remote/Local (RL):This function selects betweenbus controlled device settingsand manual settings effectedwith switches, hardware con-trols, and the like.

7. Parallel Poll (PP):This function enables a bus -connected device to send itsstatus information in responseto an identification prompt fromthe CONTROLLER.

EE

October 198734

5

BUSY

ACAMG

DATA

STROBE

BUSY

AMMO

DATA

STROBE

ICS CAL

I

5 oar!

rtNItOA pa 0BiAll

Data licA:n=e

DATA

BUSY

ACA

pa onisL)

*Proagatase Darr Tame less than 200 Ns. =",.%4

Version AMX -82

Version 8RX 80

Version C

87045-5

Fig. 5 The relative position of the ACKNLG pulse is different for 3types of printer with a Centronics interface.

6a

0

ha3AC

IEC Bus

bDAV 7

BRED

MAC

IEC - Sus

1 0

0

0

STROBE

L BUSY

ACAtaG

37C-15 -Ea

I I

I

2O ars 20

STROBE

[BUSY

E7C45 - 6

Fig. 6 The handshaking signals used for a Centronics and an IECinterface differ in respect of timing and polarity.

CliSCOPICT ALL MITERFACECABLES BEFORE PENTORSOUG

0 COtalCeNCE 7 -EST.Ca nnbEscz

TEST

8. Device Clear (DC):This is the individual or generalreset command for bus -connected devices.

9. Device Trigger (DT):This function enables a localprocess in the device to takeplace.

10. Controller (C):This function is indispensablein any IEC bus where data isconveyed via different paths.

From this summary it is clearthat the IEC-Centronics inter-face about to be describedshould at least comply with theAcceptor Handshake function.

A matter of micro-secondsA complete description of allthe functions, specificationsand technical requirementspertaining to the IEC standardwould be beyond the scope ofthis article. None the less, a dis-cussion on the difference intiming with respect to the Cen-tronics standard is useful fordetailing the operation of thepresent circuit.Datawords of 8 bits can be con-veyed reliably via a Centronicscompatible interface thanks tothe use of the 3 handshakinglines STROBE, ACKNLG andBUSY, which operate as shownin Fig. 5, with 3 alternativetiming arrangements, A, B andC, depending on the type ofprinter. It was already notedthat the logic levels used for theIEC interface are inverted withrespect to the Centronics stan-dard, and this explains the useof 8 inverters on the datelines.The crux in designing the IEC-Centronics interface is the con-

nection of the asynchronoushandshaking signals: DAV toSTROBE. NRFD to BUSY, andNDAC to ACKNLG. Figure 6ashows that the DAV signal (1)can simply take the function ofSTROBE, even if it is con-siderably longer than usual.The BUSY signal from theprinter (2) need merely bepassed through an inverter todrive the NRFD input on theIEC bus. Converting ACKNLGinto NDAC (3) is not so simple. Itwas already seen in Figs 5a. 5band 5c that Centronics compat-ible printers may differ inrespect of the position of theACKNLG pulse relative to thetrailing edge of the BUSYsignal. For a printer of type A, itis sufficient to invert ACKNLGfor obtaining a proper NDACsignal. Printer types B and C,however, call for a more com-plex way of obtaining NDAC. Amonostable multivibrator trig-gered on the trailing edge ofACKNLG would do for printertypes A and B. while a a similarcircuit, but triggered on theleading edge of BUSY is re-quired to obtain the NDACpulse from a printer of type C.In practice, it has appeared thatthe circuit designed for "typeC" printers gives acceptableresults on type A and B printersalso. The circuit diagram of Fig.7 shows that the ACKNLG signalis only used to drive a LED.while BUSY is applied to dualmonostable IC a. MMV, andMMV2 provide a delay of 200 isand 20 Ns respectively to ensurethat the NDAC pulse occursalways within the active periodof NRFD-see Fig. 6b.

ConstructionFig. 8 shows that the printed cir-

EE

October 1987

7

24 (25) way IEEE 435Calfltett4

MIM

DAV

0101

D102

0103

0104

D105

0106

0107

I1RFD

MIM

liDAC 0

1

2

4

4 5

6

7

9

12

3

5V

9.

5V

°L 16 ICL.IC1 1C2 1C3

K2

12

?lY

R

668

f

IN

1

R21

N3

6

N4

N5 s

NS

N7

_ 8 111E1111111119

4

5V

CI

R

ECI3

3k3

15n

la

15

C2

1n5

13

N8

N9

N11

_r 5 10

t3 7

N10

R12

ffff 4

90 iol7 A B

MMV2

o6

sl

10

11

2

141...N6 = IC1 = 74LS 4N7...N12 = IC2 = 74LS14MMV1, MMV2 = IC3 = 74LS221

36 wayCentronicsconnect:4

87045 -7

5V

ACKULG

STROBE

7

rm

DI

112

D3

05

06

07

BUSY

Min

Fig. 7 Circuit diagram of the IEC to Centronics converter.

cuit board for the interface has4 wire links, which must not beoverlooked while populatingthe board. Resistors R4... R2I

are standard, miniature, typesmounted upright and common-ed with a length of horizontallyrunning wire to effect the con-nection to ground (114...R12incl.; WI) or +5 V (1113...R21incl.; W2). Flat ribbon cable canbe connected direct to rows IC,and K2. The cable connected toICI is terminated in a 24 -wayIEEE 488 plug, that to K2 in a36 -way Centronics plug. Referto the circuit diagram and Fig. 2for the pin numbers on theseconnectors.It should be noted that the IEC-Centronics interface does notconvey all of the printer signalsfound on a Centronics interface(PE, ERROR. SLOT IN, etc.). Thesupply voltage for the interfaceboard is applied via pin 18 ofthe Centronics connector. Mostprinters can easily supply therequired current. The length ofthe Centronics cable should notexceed 2 metres, while the IECcable may have a maximumlength of about 4 metres. D

Parts list

Resistors 1± 5%1:

11,-,R2= 18K

RI= 27ORRd . Riz incl.=3K3Ri]...Rzi incl.= 6K8

Capacitors:

C1=15nC2=1n5C1= 10p; 16V

Semiconductors:

DI= yellow LEDICI;IC2= 741S14IC3=74LS221

Miscellaneous:

PCB Type 87045 Mot availablethrough the Readers Services).

Fig. 8 The printed circuit board for building the IEC-Centronics interface.

...b.r1BEz11

LOW -NOISEMICROPHONE PREAMPLIFIER

A quality preamplifier that can be configured for low and highimpedance, as well as balanced and unbalanced, microphones.

Most dynamic microphones ofEuropean make (AKG, Beyer,Sennheiser) have a character-istic impedance of 200 Q, whilethose of Far Eastern origin areusually terminated in 500 to600 Q. The impedance of elec.tret condenser microphones istype specific, and usually in therange from 600 to 1000 Q. Mostmicrophones have a sensitivityof 2...3 mV/Pa. The termina-tion impedance, i.e., the inputimpedance of the preamplifieror the microphone transformer,should be equal to or higherthan the impedance of themicrophone. The transformer isoften precisely matched to themicrophone impedance(power matching), while pre-amplifiers give optimum per-formance when the terminationimpedance is slightly higherthan the microphone im-pedance (voltage matching).The use of a transformer with aan impedance ratio of 1:10 or1:15 relaxes the requirementsfor the sensitivity and thesignal-to-noise ratio of the pre-amplifier. However, the circuitmay still be susceptible to humand noise when the transformeris housed in the microphone.Obviously, this calls for high -quality microphone wire. Humand other interference isminimized when the micro-phone preamplifier has asignal-to-noise ratio of 70 dB ormore. Balanced systems (themicrophone, cable, and pre-amplifier input) are known fortheir high immunity to noise.

Circuit descriptionThe circuit diagram of themicrophone preamplifier isshown in Fig. 1. The amplifiercan be configured for use withbalanced and unbalancedmicrophones. Componentvalues for the unbalanced ver-sion are shown in brackets.

Components whose value is notshown for a particular versionare not required (also consultthe parts list).Balanced version: the inputsignal is applied to the + inputsof operational amplifiers ICIand IC2. Resistors RI ...RA incl.determine the input im-pedance. When jumper A is fit-ted, the output signals of theopamps are subtracted in IC3for effective suppression ofhum and noise. Due to thehigher number of active com-ponents, the S/N ratio of thebalanced version is a fewdecibels worse than that of theunbalanced circuit.Unbalanced version: wire linkB is fitted, so that IC3 functionsas a non -inverting amplifier. IC2and IC3 are not required. Theinput impedance is determinedby R3, R4 and RI,. The micro-phone signal reaches IC3 via CIand the wire link fitted in pos-ition R9. IC3 and ICA raise the in-put signal to enable driving theline input of an AF poweramplifier.The input impedance of thepreamplifier can be switched

between high and low by con-necting a switch between Syand ground, and Sr andground-the former is not re-quired for the unbalanced ver-sions. If necessary, the inputimpedance of the preamplifiercan be altered to match a par-ticular microphone. The inputresistance of the balanced ver-sion should consist of 2 equalresistors with a value of halfthe required termination im-pedance. In the unbalancedversion, R3 and RI may be omit-ted, so that RI, alone deter-mines the input impedance.

Construction and useThe printed circuit boardshown in Fig. 2 can be used forconstructing both versions ofthe preamplifier. Separate partslists are given to avoid construc-tion errors. Fit jumper A or B asappropriate, and do not forgetthe 2 wire links. Capacitors of 3different pitch sizes can be fit-ted in positions C, and C4. Fig-ure 3 shows prototypes of themicrophone preamplifier fittedin diecast enclosures to ensure

Low noise microphone preamplifier

Technical specification

Supply voltage:Current consumption:

=9...15 V± 7.5 mA (unbalanced version)± 15 mA (balanced version)

Signal-to-noise ratioNE5534: -87 dB (unbalanced version)

-81 dB (balanced version)OP -27: -89 dB (balanced version)

-83 dB (balanced version)Distortion: < 0.003%Voltage gain: 40 dBInput resistance: 24 kQ or 680 Q

(unbalanced version.45 kQ or 660 2 (balanced version).

Measurement conditions:

RL = 41(7; Uo= Vams 'A 0 dB; f = 1 kHz. 'SiN ratio measured with input short-circuited.

robustness and freedom of in-duced noise.The symmetry of the preampli-fier, and hence the attainablesignal-to-noise ratio, dependsmainly on the quality and thestability of the componentsused around ICI, IC2 and IC3.Equally important, however, isthe use of a high -quality micro-phone and a suitable cable. Sv

EE

October 1957

1 40

Sy

Sx

R2

n

R3

R4

n

R6

H

(471E5)

IC1

R5

R7

2

(6810)

31C2

1C1 -.1C4 = NE5534; OP27Dl; D2 = 1N4148C7...C14 = 100n

ff\A R

J1

/El (loon)

R9

(jumper)

Ub (9...15V)

+

0 7$Ub (9...15v)

2

3

R11

H

C2

11117221

RIO

EMSI(1800)

1C3

(47k5)

C3_I 1122_(2201

2

R13

B

R12

(8625)

1C4

7p5

(16001

C46

R14

B 110081

CST= DI-i0,7,

® 0.1.C6 02

C= X10176V

c

ci (/(Cl 1C2 103 1C4

; ;CE1±

T57058.1

Fig. 1 Circuit diagram of the low noise microphone preamplifier.

Fig. 2 The printed circuit board for the microphone preamplifier.

Parts list

Balanced version

Resistors (±1%):

RI;Rd=332RFR2:Rs=22K1FRs;Rr =6K81FRe= 1K5F

RERs=1K21FRio;RII:R12=5K62F1317=4K75F

fil<= 100KF

Capacitors:

Cs;C2= not requiredC3 =22p; styroflextpolystyreneC4=1175; MKT*Cs;Cs=100; 16 V; radialC7 CIA incl.=100n

Semiconductors:

DI;D:=1N4148ICI ...ICA incl.=0P-27 orNE5534

Miscellaneous:

PCB Type 87058 (availablethrough the Readers Services).

Parts fist

Unbalanced version

Resistors (+1%):

fl1:R2;Rs;Rs;137= not requiredR3;Ril=47K5FR.I=681RFRs=100RFRs= wire linkR 1KOF

R12=8K25FR14 =100KF

Capacitors:

C1=1µ0; MKT*C2:C2= 22p; styroflevpolystyrene

C4 = 1115; MKT*

Cs:Cs=10y; 16 V; radialC7...Cis incl.=not required

Cll.. .C14 Ind. =100n

Semiconductors:

DI;D2=1N4148ICI;IC2= not requiredICEIC.4= OP -27 or NE5534

Miscellaneous:

PCB Type 87058 (availablethrough the Readers Services).

MKT capacitors are Siemensstyle, blue cased, TypeB32529. Available fromElectroValue 28 St JudesRoad Engiefield Green Egham Surrey TW2O OHB.Telephone: (0784) 33603.Manchester branch: (061 432)4945.

Fig. 3 Prototypes of the preamplifier housed in Eddystone enclosures.

EE

October 198738

14 -BIT DIGITALTO ANALOGUE CONVERTER

A high resolution D -A converter that enables computer control oftest, measuring, and electrophonic equipment.

Most D -A converters (DACs) thatfind applications in home-madeperipheral equipment are 8 -bittypes. The converter chip usedin this project. however. is a14 -bit type originally designedfor use in compact disc players.The programmable number ofsteps of this chip is 224, or16,384. The present converterboard has a parallel input forready connection to most typesof microcomputer. Appli-cations of the board include acomputer -controlled functiongenerator (see the above photo-graph), a power supply con-troller, or a high quality driverfor synthesizers and effectsequipment. Many other appli-cations are within reach pro-vided the appropriate softwareis available-and that is wherethe programmer's own ingen-uity and creativity come in.

The Type TDA154014 -bit DACThe standards, and thereforethe manufacturing technology,for ensuring the accuracy of a14 -bit DAC are quite differentfrom those applied to, say, 8 -bitconverters. In essence, the con-ventional DAC based on the use

of a R -2R ladder network (Fig. 1)requires no trimming if up to 10bits are converted; the stabilityof the resistors is simply in-creased to meet the requiredstandard. For DACs with morethan 10 bits it becomesnecessary to calibrate the re-sistor ladder by means of a pro-cess called laser trimming, but

Table 1

TDA1540 14 -bit digital to analogue converter

Supply voltages:SIN (full scale sine Wave)at analogue output:Non -linearity (Ta -20 to ÷70 °C):Maximum clock frequency:Full scale temperature coefficientat analogue output:Total power dissipation:

±5V; -17V

85 dBLSB

12 MHz

i30.10a K 1350 mW

this also has its practical limi-tations. Applied to 14 and 16 -bitDACs, the calibration of thechip would be upset when thisis fitted in its plastic or ceramicenclosure.A different method of dividingthe current in the network is re-ferred to as dynamic elementmatching-see Fig. 2a. A 14 -bitversion of this circuit can attainthe required accuracy withoutthe need for trimming, stabiliz-ation, or other adjustments. Thecurrent supplied by the refer-ence source is divided in 4equal currents by 4 matchedtransistors. It is evident that theinevitable production toleranceon the transistors causes smalldeviations, if, from the idealcurrent distribution:

(I+_11)+(1+_1/2)+(1 .113)+(f+J/4) = 41

EE

October 1987

Fig. 1 The accuracy of an R -2R ladder network is insufficient for a14 -bit DAC.

whence

1/1+1/21-1/3+_1/4 = 0.

The 4 currents (ii-i/n) are alter-nately fed to the 3 outputs. Thiseffectively time -averages theerror currents 1!, so that out-puts 1, 2 and 3 carry currentswhose average values arerelated as I:I:2J = 1:1:2 (see Fig.2b). Ripple currents are sup-pressed with the aid of an R -Cfilter. The ripple frequency is50 kHz, i.e., one fourth of the os-cillator frequency. The R -Cfilters also ensure that theaverage current is used in theD -A conversion when sampleswith a frequency of more than50 kHz are applied.Figure 3 shows the internal or-ganization of the TDA1540 14 -bitDAC from Signetics. The cur-rent divider for the most signifi-cant bits, the reference and theamplifier form a current mirror.The reference current sourcealso supplies the current for themost significant bit, eliminin-ating the need for additionalfiltering. A different current div-ider is used for the least signifi-cant bits. To avoid the need foran increase in the negativesupply voltage for the chip, thecurrent is not divided by con-necting matched transistors inparallel, but by designing andmanufacturing these in accor-dance with the required distri-bution.For optimum operation the out-put voltage should be kept vir-tually nought, since thisensures the effectiveness of the

R -C filters while avoidingspurious products caused bythe switch circuitry. This is im-portant because samples seemto come off the disc at a rate of176,400 per second when theCD is a type with quadrupleoversampling. The high sam-pling frequency lowers theoverall resolution to some ex-tent because the currents areaveraged over a longer period.A compact disc is essentially aserial storage device, and theTDAI540 is, therefore. designedfor serial processing of digitaldata. The most significant bit isfirst fed into the shift register.Data is stored in a latch toeliminate spurious analogueoutput currents. The principaltechnical specifications of theTDA1540 are shown in Table 1.

From parallel toanalogue informationThe quickest and simplest wayof outputting computer data to aperipheral device is via a paral-lel port. As already stated. theTDA1540 handles serial data,but the standard serial (RS232)port on a computer is generallytoo slow for direct interfacing.A parallel -serial converter istherefore required to enablestraightforward driving of theDAC board with the aid of 2parallel output ports.The block diagram of the 14 bitDAC board is shown in Fig. 4.The 14 bits are applied as 2bytes, which are converted intoserial format by a shift register.

Fig. 2 An accurate current ratio is obtained by time -averagingations Ain in a distributor circuit.

The most significant bit (MSB) ofeach byte is not used. Lines PA6and PAY are used for startingthe shift register, and also indi-cate which byte (MSB/LSB) is tobe loaded. The control circuitryon the DAC board activates theRDY line to signal readiness forreception of the next 2 byteswhen the shift operation is com-

devi-

plete, and the D -A conversionhas been started.A transimpedance amplifier atthe output of the DAC convertsthe output current into a corre-sponding output voltage.

Circuit descriptionWith reference to the circuit

EE

October 198740

3

[0-78

SHIFT REGISTER

LSB V V. PASS

LATCH

: 1 : 2 : 4 :

OSCILLATOR &4 - BIT

SHIFT REGISTER

analogueoutput

i

0 E00000

: 1 :

: 1 :

CD

CO

: 1 : 2

: 1 :

O

00

0

: 1 :

ilref

S7160.3

Fig. 3 Block diagram of the TDA1540. The filter capacitors are fitted externally.

4 ORGY

o"6oP*7

CLK

CONTROL

SHIFTREGISTER

0 TIM 1540

137160 -4'

Fig. 4 Block diagram of the complete 14 bit DAC.

diagram of Fig. 5, the DACboard is connected to the com-puter ports via connector Kt. APIA (peripheral interfaceadapter) for the CommodoreC64 computer was described inReference (I). while MSX usersare referred to Reference (').The operation of the circuit isexplained with reference to thetiming diagram of Fig. 6, andthe flowchart for generating asawtooth voltage shown in Fig.7. The numbers in betweenbrackets refer to the pulses atparticular points in the circuitdiagram. The timing diagram isvalid for a single FOR/NEXTloop. At the onset, data isloaded into the shift registers.ICs and ICI°. The least signifi-cant byte on port lines PBx isloaded by making PA6 logiclove PA6 is then made logichigh, and PA7 logic low. Thismust happen simultaneously toprevent N3 prematurely supply-ing a start pulse. Now the circuitcan load the second (MS) byte,whose bit 6 and 7 are kept logiclow to ensure the correct oper-ation of the converter. PA7 issubsequently made logic highto enable the circuit to startshifting data into the D -A con-verter. Bistables FF1 and FFzenable the clock signal (4) to befed to the shift registers.Counter IC: counts the numberof output bits from the shiftregister. When the 15th and 16thbit have been shifted out, andthe 14th bit appears on outputOtt. Nis is enabled by N7 topass clock pulses (7) to theDAC. IC7. After a total of 16clock pulses. all bits areavailable in the DAC. point (6)goes high, and N12 supplies anoutput pulse (8) that causes the14 bits to be latched in the DAC,and FFt and FF2 to be reset.The ready signal (RDY) goeshigh, and the computer can out-put the next 2 bytes. The pulsediagram shows that the the cir-cuit is not activated until the bitsare loaded. This arrangementeffectively prevents the pro-duction of spurious signals.Operational amplifier ICstranslates the output currentfrom the DAC into a corre-sponding voltage. A virtualground potential is created toensure a low offset at the outputof the TDA154 O. The maximumoutput voltage of the opamp is4R2 V, where R2 is given in kip.The minimum load impedanceis 600 0.Separate +15 V and -17 V sup-

EE

October 1987

5X I

PAZ

PAlP42PA3

PAZ

PASLOAD Lsaita PASLOAD KS Byte PA7

DO KtDI PSI02 PS2D3 PS304 PSI135 PBS

06 PS607 pg/

ROT CAS

mi.

I Mgt

W

R6

Ni N2

3

C21

100p

6

5V

4r)

3 CLK e 0FF1

OP

10

16)5

6

0FF2

P

Si

ft

12

SV

N11

11

14

2

N13

10

K1 NS -

000o

00

C>

fliOO

O0O

tg

Zfl

C24

0

C)

B 1C9 SEF113

D 74HCT

55 G 165 CLK

*" T1II 9t5

12

"3

5V

11 to 13

A g

IC10CLK

0

E 74F HCTG 165HO

2

2

5V

3 8CU(

1C4E

74HOT

"R 161wr .1,<au01 41 11

9

216

C>

x112

s-

85

C 0

13 P 017V

N 1, NZ. N5, tt6, N11, N13 = 1C3 = 74HCT04N3, NI, NB.N12=102 7414132N7. N9,1110 = IC1 = 74HCT27FF1, FF2 = 1C11 =74HCT74

2

17V

C6

B2009 11 22

our

15V00211.

1.00n

R24 82B

2

25 LE - -Iry ..v

8ey

:****2"4:::**

CP 1REF1

DATA IC7

TDA1540

13RaA Rag

CfE3

I RE/ 3 17 italCi9

IC8

7

NE5534

6

Ca

220

6

0I7V

47160-5

Fig. 5 Circuit diagram of the 14 bit DAC.

plies are required to feed theDAC board. Standard designswith a Type 7815 regulator(+15 V), and an LM337 (-17 V)are adequate for this purpose.Resistors R3 and R4 are highstability. (1%) types. The valuesstated for R2, R3 and R4 ensureoptimum performance of theconverter. R2 and R4 may bemade from series connectedresistors as shown in the circuitdiagram and the parts list.

ConstructionThe ready-made printed circuitboard for building the con-verter is shown in Fig. 8. Besure to fit all wire links shownon the overlay; the 2 long linksin between 1C2 and 1C3 shouldbe made in insulated wire. Thevoltage regulators are fitteddirect onto the board, and may Fig. 6 Timing diagram for a single sampling cycle.

EE

October 1987

7

start sawtooth

initialize 1,0 portPA6 = PA7 = "1"

loop

FOR X = 0 TO 2'14-1

MSB = INT (X/2561LSB = X-(MSB2561PA6 = "0"place LSB in shift registerPA6 = "1": PA7 = "0"place MSB in shift registerPA7 = "1": REM start conversionwait until done

NEXT X

goto oop

Fig. 7 Flowchart for generating a sawtooth voltage.

Table 2

PS2

-;:sat__:

RE.,,L AS "get n.--n;ne -75-antic= natttne

EiC-... MACHINE CODE

.7 ...DC:E8Z AND AS.-- THEN 1.9.0 'select ..tie-AN _ 7;8.81N :13

,,NL: A! 1' ,!7 13. THEN 190

u 39.:VERVER.&HCZ-058 EN - -:DEFGE;ReaHC0.35

L..DATE : 430;03TO 270E7,:-. -_de

anr:ws cri screen

:Tv!

1.A iNE....7

;GI IT DE.M56S7:7,

RETRNreel-ETATLi

Fr!7 USING

- : -

1HCOZE.-:RETURN

SIN,:E. X MOD 2E8

117 DB;LSS -1da3 shiftreg. 3'read HIV_Idad shirtreg. tead FICsenerate 5,:51.11 pal:2e

T1-1,1RTE--;HEXS.D1.18

8.-;-Ct= -.HEX5 _

1:PICT VOLTAGEVOLTAGE

PRINT- C. SINE -WAVE -

be fitted with small heat -sinks. Itis recommended to fit theTDA1540 in an IC socket.

Samples and filtersThe number of samples fed tothe DAC board depends on thespeed of the process to be con-trolled by the computer. Themaximum sample rate of thecircuit is 10 MHz/16 = 687,500per second, but this is not likelyto be attainable in view of thetime required for the computerto load the shift registers. As arule of thumb, the sample fre-quency is at least 2 times thehighest frequency of theanalogue output signal.A filter is required when theDAC is used for audio ormeasuring applications as in,for instance, a computer -controlled function generator.It can be shown that the

analogue output of the DACsupplies a modulated signalwith spectral impurities due tomixing products. Figure 9ashows a spectral analysis ofan audio signal sampled at44.1 kHz, without digital filter-ing. It is seen that mixing prod-ucts are generated above22 kHz. These spurious signals-and possibly intermodulationproducts that arise from them-can become audible in theamplifier, and call for an ex-tremely steep -skirted low-passfilter to achieve sufficient sup-pression. The need for a filter isalso evident from the fact thaton a CD a 20 kHz sine -wave isrepresented by only 2 samples.Obviously, this sine -wave canonly be restored with the aid ofa filter. In a compact disc playerusing quadruple oversampling,the sample frequency is176.4 kHz. Figure 9b shows thatthis relaxes the requirements

Table 3

Cc vow,' o re 054

REM SELECT DORA:Rai ALL OUTPUT

1-0 ;REM SELECT DRA..713.0 :REH SELECT DDRB

7: F:KE D8.255 :REM ALL OUTPUTE0 F-8:5 :a.f, :REM SELECT DRS

18.Tx :EFATE MACHINE CODE .aTO 85

11I1 READ A120 PORE SC:50-tX.A130 NEXT X190 REM **. nA:N FRCAGRAM200 CH21:2E,':i-1NT CHRS;147):REM CLEAR SCREEN.:1 1:2TR :0,1,0

7F AS 5-- ANL: :114310E.0 THEN 213AND T5E,ICE 52 THEN 217

-:- AND AS AND AS, -3- THEN 210- THEN CHCaCE.At-1,CiAS11F..-; :HEN ,102U3 EZZO:SYS S CO3A

7KEN 1,000

AS

'8 0.1-=2.Z2.:G=.189.128.141.00;222. .M222_173,00. 194

=5 :,:.:-1.0.222.232.209.229201.63,208,219;169.0

_.;i.169;192,141,0,222,53,9e

DDL.173.1.194.11,2.1211.273.0.194;141.2.222

I _ATA00 REM...

FOR 1.1.3 7: : :7EF.12320 X=8191.5-=:1: ''S1N it3030 MSBeINT X3040 PORE DA.SDc3050 PORE DB,LSE3060 FJEE 0A.34£2070 POKE DS,MES3080 POKE DA.SC03590 NEXT U;RETURN6003 REM INPUT ROUTINE8010 INPUT -ENTER VALUE -;S7010 T.TE S:200.INTtB/2S61

- c'231,13-INTIB/2560256- :000;RETURN

EE

October 1987

Fig. 8 Printed circuit board for building the 14 bit DAC.

for the slope of the low-passfilter, and makes it possible touse a third -order filter withBesse! or Butterworth charac-teristics and yet attain morethan adequate performance.

SoftwareTable 2 lists a program forgenerating a direct voltage, asawtooth voltage, or a sine -wavewith the aid of an MSX com-puter. A similar program for theCommodore C64 is shown inTable 3. It should be noted thatthe addresses of the input/out-put devices may have to bealtered as required. In the MSXprogram, the loading of the D -Aconverter is effected in lines470...510, in the C64 programin lines 3040...3080.

D

References:

(11 Computerscope - 2. ElektorElectronics, October 1986,p. 44.

C2' MSX Extensions - 4. ElektorElectronics, January 1987.

Parts list

Resistors I ±5%):

Ri =2K7Fiz=2K5 (1K0+1K5)R3= 82RFR4= 620RF (470RF+150RF)Rs =4K7R6 = 2K2

Capacitors:

Ct . C4 incl.;Cli:C22 . C26incl. = 100n

Ca:C1.1...Cta incl.= 10nC6 = 820pCi=1n0Cs= 22pCs = 470nCm= 220nC12 =47nC13=2211

C19= 1n5Czo;Czt = 100pC27= 2112: 16 V; axial

Semiconductors:

ICI =74HCT27IC2= 74LS132IC3= 74HCT04IC4= 74HCT161ICs= 7805ICs = 7905IC7=TDA1540ICa=NE5534ICs;ICio= 74HCT165ICit=74HCT74

Miscellaneous:

Xi = 10.000 MHz quartzcrystal, 30 pF (AT) series res-onant: HC1811.1 enclosure.

Kt = 20 -way, double row, maleheader.

PCB Type 87160 {availablethrough the Readers services).

Signetics-Philips MullardHouse Torrington Place London WC1E 7HD. For UKdistributors see Infocard 509(EE May 1987).

It is regretted that software forcomputers other than the C64and those in the MSX series isnot available.

kaudio band/22 44.1

Fhuhuh176.4

f [kHz]

22

8711.0 - 9

175.4f [kHz]

Fig. 9 Output spectrum of a DAC at a sample rate of 44.1 kHz (a) and 176.4 kHz WI.

EE

October 198744

RECORDING/PLAYBACKAMPLIFIER

This amplifier enables accompanying slide presentations withstereo commentary or music whilst using a separate track on the

cassette recorder for controlling the slide changer.

This simple to build amplifiermakes use of a 4 -track re-cording/playback head fittedin lieu of the 2 -track head in anordinary cassette recorderused for audio-visual presen-tations. Four -track heads can bepicked up occasionally fromsurplus outlets, or purchased asa servicing part for auto -reversecassette players. The proposedsignal assignment on the4 -track head is shown in Fig. 1.The non -used track in betweenthose assigned to the stereoprogramme and the controlsignal ensures acceptablelevels of crosstalk. The pro-gramme and the slide controlsignal can be recorded separ-ately. If required, the controlpulses can be erased by revers-ing the cassette and recordingsilence.

Circuit descriptionThe circuit diagram in Fig. 2shows that the recording/playback amplifier is set uparound the Type TDA1002A in-tegrated amplifier fromMullard. Although this compo-nent is not aimed at the highquality market, its technicalqualities are still adequate foruse with most types of (semi -portable) stereo cassetterecorders or decks commonlyavailable. The TDA1002A re-quires relatively few externalcomponents to make a versatilerecording/playback amplifier.As shown in the circuitdiagram, the chip comprises apreamplifier and a recordingamplifier with automatic levelcontrol (ALC). The controlrange of the ALC circuit isstated as 50 dB ±2 dB.When 4 -pole toggle switchSi is set to RECORD as shownin Fig. 2a, the slide controlpulses are applied to pin 1 of

the TDA1002A via switch sec-tion c and terminal C. Also, theRECORD LED lights (section a),and one side of the symmetricaloutput of the record/playbackhead is grounded. Since ter-minal D is connected to E (sec-tion d), the preamplifier workswith feedback circuit C1 -R3

connected in series betweenoutput pin 4 and input pin 2.The amplified signal is availableat the output of the circuit, but itis also fed to the input of the re-cording amplifier (pin 8) viaRa-CT, and the input of the ALCcircuit (pin 6) via Rs. The inputof the recording amplifier isheld at a fixed potential with theaid of voltage divider Ri1-R10-R9.The negative feedback networkbetween output pin 9 and inputpin 7 is composed of R12 -R15incl. and C11 -C14 incl. The ALCcircuit acts on the output of therecording amplifier via1112-Ria-Cg. The limiting time(10 ms typ.) and the recoverytime (35 s typ.) are fixed with C15and C16-1119 respectively. Theamplified and limited re-cording signal is fed to the headvia Clo-RIG, terminal A, switchsection b and R1.When Si is set to the PLAY mode,

terminal A is grounded viaswitch contact b, LED DI is ex-tinguished, and the playbacksignal from the head is fed tothe input of the TDAI002A.Switch section d selectsnegative feedback networkR5-05-116 between the outputand the input of the preampli-fier, which is so dimensioned togive the appropriate gain. Notethat the ALC and the recordingamplifier are ineffective in thePLAYBACK mode. The outputsignal can be fed to the avail-able slide change circuit.The circuit is fed from aregulated 10 V supply set upwith IC2. The unregulated inputvoltage should not exceedabout 15 V. It may be necessaryto redimension R20 in accord-ance with the regulated orunregulated voltage available inthe cassette recorder.

Construction andsetting upThe layout for the printed cir-cuit board for building the re-cording/playback amplifier isshown in Fig. 3. Note that theboard does not hold the partsshown in Fig. 2a. It is rec-

1U A

B

C

D

A = track RB = track L

C = not usedD = slide change track

Fig. 1. Suggested track assignment on a 4 -track head.

ommended to fit the completedPCB at a suitable location in thecassette recorder. Most types oflow cost, modern cassette deckhave plenty of space inside tohouse a small additional PCB,and generally do not presentproblems as regards the supplycurrent for the proposed ampli-fier. The 4 -pole toggle switch,Si, and the LED, D1, are fitted onthe front panel.Carefully remove the existingstereo head, and make sure tohave connection data of the4 -track head available beforethis is fitted. In some cases, thenew head requires a fewmodifications to be carried outon the existing head mountingassembly, and possibly to theazimuth adjustments also. Referto Fig. 1 and connect the two re-cording/playback channels ofthe head to the existing cir-cuitry in the recorder. Connectthe head section for the slidecontrol signal to 111-R2 (these arefitted direct onto Sib) via a shortlength of shielded, symmetricalwire, grounded centrally at ter-minal B as shown in Fig. 2a. Itshould be noted that the equal-ization characteristics of theTDA1002A are dimensioned forFe cassettes only. The total gainof the device is about 40 dB atan average distortion of 0.5%.The maximum input and outputvoltage are 20 mVnits and 2 Wirsrespectively. The input im-pedance is about 16 kQ. De-pending on the sensitivity ofthe head used, the stated valueof R16 may have to be slightlyaltered to ensure the amplitudeof the recording signal.Resistors R3 and R4 determinethe gain of the playback ampli-fier. Low frequency oscillationmay occur when the amplifier isdimensioned for a relativelylow gain.Test the newly installed 4 -track

45 EE

October 1987

2a

RECORDPLAY

RECORD

511

RECORD

0pI t -N

0

OC

OB

OF

OE

head by first playing a pre-recorded stereo music cassette,or, if available, a test cassette.Adjust the head until the qualityof the playback signals is ac-ceptable. Rewind the tape tothe start, and replay it whileusing the recording/playbackamplifier for recording theslide control signal on the thirdtrack. Stop the tape, rewind it,and check whether all signalsare played back at acceptablelevels of distortion andcrosstalk. Slide change signalsof a wide amplitude range canbe recorded without causingtape saturation, thanks to theALC circuit in the recording/playback amplifier.

2b 520 ,A

R16

16

RIB

Ell

13 6

CIO

I10WIRV

C9-10-*106166

R11

10

C17

CB

479166

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$01,

PRE ARP

IC 170A 1002 A

A. L C. REC ARP

Cl

IC 278L10 0

CIS

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5 4 12

106 16V

R3 RS

R6

fl

C5

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C1RM2 C3

79 710601.11V

R4

gR7

CIS 619=1

146716V

la

CSLIi73616V

C16

2209I6V

R13

fl

C11

2209

612

ELM

R15 614

C12 C14 C13 R9nim MIR

1729 79 175r,16V

BMOM

'p57456 -2D

Fig. 2. Circuit diagram of the recording/playback amplifier.

Parts list

Resistors 5%1:

RI:112=22R

RS = 6K8

R4=220RRs =- 560K

R6= 12K

R7= 100R

RS:1111=33K

Rs= 1COK

Rao =68K

R12 =2K7

Ras= 1EOR

11,4;1116=27K

Ras =2K2111;;Rl6 = 10K

R/9=100R27.r= 1K5

Capacitors:

Cr,C4;Cs;Cs;C10=10,2; 16 V; axial

C;;Cia=3reCa =1001;16 V; axialCs;C17= 10nC7= 100n

C6=4714 16 V; axialCal =220pCa2=274r; 16 V; axialCu = 15nC15 = 4y7; 16 V; axialC16= 220y; 16 V; axialC76 =330x1

Ca s =820p

Semiconductors:

Da= red LEDICI =TDA1002A1C2=78L1O

Miscdaneous:

St miniature 4 -pole toggleswitch.

4 -track recording/playback headfor eAste.tte recorder.

It is regretted that the PCB forthis project is not availablethrough the Readers Services.

Avafiable from Universal Semi-conductor Devices Limited (ad-dress and telephone numberappear elsewhere in thismagazine).

+ Available from CricklewoodElectronics Limited (address andtelephone number appearelsewhere in this magazine).

Fig. 3. Track layout and component mounting plan of the PCB for building the recording/playback amplifier.

EE

October 198746

SSB ADAPTER

A low-cost add-on unit that enables single-sideband reception onvirtually any AM short-wave receiver.

Every experienced short-wavelistener knows that single side -band (SSB) transmissions cannot be received unless aspecial detector is installed inthe receiver. Unfortunately,however, an SW receiversuitable for SSB reception isgenerally far more expensivethan an AM/FM general cover-age, radio set having adequatesensitivity and selectivity. Tothe dedicated SW listener,amateur and utility stationstransmitting SSB signals areoften more interesting than(broadcast) AM stations in viewof their uniqueness, and thelarger distance covered. SSBtransmitters are more economi-cal than AM transmitters asregards bandwidth and powerconsumption, due to the ab-sence of the carrier and thesecond sideband.

Carriers andsidebandsIt can be shown that the RFpower contained in the carrierand one sideband of an AMmodulated RF signal is redun-dant, because it is not, strictlyspeaking, needed to convey in-

formation to the receiver. Forthis purpose, one sideband suf-fices. The RF output signal of anAM transmitter modulated witha single, sinusoidal frequency isshown in Fig. 1. The instan-taneous amplitude, U, of the RFcarrier is a function of the am-plitude of the modulating AFtone, which can be recon-structed by drawing a linealong the peak excursions ofthe RF voltage (the envelope

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waveform). Mathematicallysimplified, this AM signal is de-scribed by the expression

/TAM = Efc(fc)i-mU c(fc + fin) ++mUc(fc-fm).

It is seen that the amplitude ofthe AM signal, IfAm, is the sumof 3 terms. The first, Uc(fc), isthe amplitude of the carrierwith frequency fc. The secondand third term are of equal am -

Fig. 1 RF output signal of an AM transmitter modulated with asingle tone.

plitude, mUc, but denote sig-nals adjacent to the carrier, i.e.,below and above fc. The factorm represents the relative ampli-tude of the modulating signalwith frequency fm. Figure 2ashows an analysis of the AM sig-nal in the frequency domain(spectrum analysis). The carrieris modulated with a single tonethat gives rise to 2 side tones,each having a lower amplitudethan the carrier. Modulating theAM transmitter with a composi-te AF signal, e.g. music orspeech, causes two side bandsrather than side tones adjacentto the carrier, and so increasesthe overall bandwidth occu-pied by the signal. Returning tothe above formula, it is readilyseen that the terms mUc(fc+fm)(upper sideband, USB) andmUc(fc+fm) (lower sideband,LSB) convey the same intelli-gence, namely the modulatedsignal, while the carrier, Uc(fc),does not convey any intelligen-ce. Evidently, the carrier andone sideband are not needed toconvey information from thetransmitter to the receiver, andthis forms the basis of the SSBmodulation method, which issometimes-more properly-

EE

October 1987

2 of

a

fc-fm fm

87662X -2a

b

U4

u.

fc "fin Mal -fm iris c frn r -m fc moan

Fig. 2 Spectral analyses of AM signals. Fig. 2a: single tone modulation. Fig. 2b: modulation with a composite AF signal.

Parts list

Resistors (-1-5%):

RI =10KRERs= 1K0R4 =100RRs = 4K7

= 6K 8

Pi =1008 linear potentiometer

Capacitors:

C1=2009 variable capacitorC2 = 6n8

C3;Cg =39nCs= 2n2Cs;C7= 100nCa =1n0CS =10nClo =22nCri =470n

Inductors:

= Neosid Type 7A1Sinductor assembly (see text)

1.2:L3=270pH

Semiconductors:

DI;D2=1N4148TI;T2;T)=BF494

Miscellaneous:

Si = miniature SPST switch.PP3 battery 19 VI and clip -onconnector.

PCB Type 87662X (not availablethrough the Readers Services).

Suitable metal enclosure.

' Neosid inductor assemblies areavailable fromNeosid Eduard House Brownfields Welwyn GardenCity Hertfordshire AL7 1AN.Telephone: (07071 325011.Telex: 25423.

or fromBecton Inductive ComponentsLimited Unit 8b Cambridgeshire Business Park Angel Drove Ely Cambridgeshire CB7 4DT.

Fig. 3 Circuit diagram of the SSB adapter for AM receivers.

referred to as SSBSC (singlesideband, suppressed carrier).In theory, an SSB transmitteruses only a quarter of thepower of an AM transmitter forconveying the same infor-mation. In an AM transmitter,half the power is "wasted" inthe carrier, the other half goesinto the sidebands. The RFpower of an (ideal) SSB transmit-ter drops to nought in theabsence of a modulating signal.Hence an SSB transmitter has afar better power efficiency thanan AM transmitter. and at thesame time occupies less band-width; relatively low power SSBtransmitters can, therefore, beused to cover considerabledistances (maritime communi-cations, radio amateurs, etc.)

without laying too heavy a claimon the available power source.

From SSB to AMThe operating principle of thepresent adapter follows fromthe previously discussed rela-tionship between AM and SSB.An SSB signal can be convertedinto AM by adding a carrier anda sideband. Both are obtainedwith the aid of an oscillator tun-ed to the receiver's in-termediate frequency (IF),which is usually 455 kHz. Theexternally generated carrierserves as the reference fre-quency against which the (up-per or lower) sideband isdemodulated. The second side -band is automatically obtained

in this process, so that a doublesideband AM signal is availablefor demodulating. The combi-nation of the AM receiver andthe SSB adapter is, understan-dably, not up to a real SSB com-patible receiver with its special,narrow band, IF section. Nonethe less, the results obtainedwith the present add-on unit aresatisfactory for relatively strong,interference -free, signals.

Circuit descriptionThe SSB adapter is a simple cir-cuit. shown in Fig. 3. TransistorT1 oscillates at 455 kHz with theaid of parallel tuned circuitCI -Li. The oscillator signal israised and filtered in a cascodeamplifier set up around T2 and

Fig. 4 Printed circuit board for the SSB adapter.

EE

October 198748

Fig. 5 The Type 7A1S inductorassembly from Neosid. 1:screening can. 2: ferrite cup. 3:iron dust core. 4: ABS formerand base.

T. The amplitude of the outputsignal is made variable with Pi,enabling optimum perform-ance with any receiver. Theadapter's output signal is con-nected direct to a length of in-sulated wire, wound as 1 or 2turns around the receiver (in-ductive coupling). The adapteris fed from a 9 V battery.

Construction andalignmentThe printed circuit board forthe SSB adapter is shown in Fig.4. Construction is straightfor-ward with the possible excep-tion of inductor assembly L, -see Fig. 5. Viewed from under-neath, the base of the ABSformer in the Type 'MS as-

sembly has 5 pins, 3 at one sideand 2 at the other. Inductor LI isconnected to the latter 2 pins.Close -wind 53 turns of20.2 mm (36 SWG) enamelledcopper wire onto the 2 sectionsof the former, and make surethat the ferrite cup (part 2 in Fig.5) can be fitted on top. Securethe winding with a piece ofSellotape. Check the continuityat the base, and fit the formeronto the PCB. Carefully slidethe screening can over theformer, then push -fit and solderits mounting tabs in the holesprovided. Make sure that thetop end of the former fits snuglyin the hole in the top of thescreening can. Tuning capaci-tor CI and level control P, arefitted as external components.

It is recommended to fit the SSBadapter in a metal enclosure toprevent spurious radiation.Set variable capacitor Ci to thecentre position, and PI to maxi-mum. Connect the couplingloop around the receiver to theadapter output. Tune the re-ceiver to an AM broadcaststation, and switch the adapteron. Adjust the core in LI with anon-magnetic trim tool until awhistle (beat note) is heard inthe receiver. Lower the fre-quency of the beat note by ad-justing LI, until it is no longeraudible (zero beat tuning).Switch off the adapter, and tunethe receiver to an SSB station.Switch the adapter on again,and adjust CI and Pt until thespeech becomes intelligible. B

EVENTS

Dataquest's 4th annual Inte-grated Circuits Outlook Con-ference, focusing onApplications Markets, ASIC's,and Telecommunications willtake place on 19th October atCentrepoint House, LondonWI, and on 20th October at theSheraton Hotel, Edinburgh.Further information fromCochrane CommunicationsLtd CCL House 59 FleetStreet LONDON EC4Y 1J11 telephone 01-353 8807

Top speakers from industry,government, and science willbe among those providingpapers at SEMI's fourth STEPconference in Brussels on 1-2October. The dinner speakeron 1 October is Gaston Geens,the Belgian Minister of FlemishAffairs. Further informationfrom SEMI EuropeanSecretariat CCL House 59 Fleet Street LONDONEC4Y 1JU telephone 01-

353 8807

The 1987 Internepcon Elec-tronics Packaging Show will beheld at the Metropole Hotel,BRIGHTON, from 6 to 8 Oc-tober. Further information fromBush Steadman & Partners Ltd The Hub Emson Close Saffron Walden EssexCB10 1HL telephone (0799)26699.

The Sixth International Con-ference on Automotive Elec-tronics will be held at the IEE.The conference is beingorganized by the IEE and the

Division of the In-stitution of MechanicalEngineers. It is co -sponsoredby automotive and electronicsprofessional societies and insti-tutions in the USA, Japan, andEurope, and alternates everyother year with the "Con-vengence" InternationalAutomotive Electronics Con-ference in the United States. Avisit to Ford Research &

Engineering Centre, Dunton,Essex, will be organized for Fri-day 16 October, at which it ishoped to exhibit and demon-strate relevant vehicles withelectronic systems. Further in-formation from ChristinaDagnall IEE Press Officer Savoy Place LONDONWC2R OBL Telephone 01-240 1871 Ext. 272.

Advances in techniques for Im-age Processing have now madepossible a wide range of practi-cal applications in Industrial In-spection, Robotics, Medicine,Document Handling, Car-tography, Defense. Transpor-tation, and Communications. Tosupport this important develop-ment field, the First Inter-national Exhibition andConference on the Image Pro-

cessing of Systems is beingheld at the Kensington Exhi-bition Centre, London, from 14to 16 November 1988. Papers forthe conference are now re-quested. The Chairman of theSteering Committee is Pro-fessor R. Grimsdale, MSc. PhD,FBCS. CEng, MIEE. Universityof Sussex, Falmer, BRIGHTONNBI 9QT. Further details fromNetwork Events Ltd PrintersNews Market HillBUCKINGHAM MK18 1JXTelephone (0280) 815226.

Information and advice aremajor features of Electrotec'87, the 4th North EuropeanTrade Exhibition for Elec-tronics, Electrical Engineering,Power Transmission and Hand-ling Technology, which will beheld from 25 to 28 November1987 at the Hamburg ExhibitionCentre. Further informationfrom Hamburg Messe andCongress GmbH Jungius-strasse 13 MessehausD-2000 HAMBURG 36 Fed-eral Germany.

Papers are now requested forthe Fourth International Con-ference on Electrical Safety inHazardous Areas, which willbe held at the IEE, London,from 22 to 24 November 1988.The aim of the conference is toreview the developments that

have occurred since the lastconference, in December 1982,on the safety of electricalequipment installed in areaswhere there is hazard due to ex-plosive gases, vapours, mists,and dusts. Those wishing to of-fer a contribution should sub-mit a synopsis of not more thenone side of A4 paper by 9 Oc-tober 1987 to Conference Ser-vices IEE Savoy Place LONDON WC2R OBL.

49 EE

October 1987

SWITCH -MODE POWER SUPPLIES

Recent advances in power semiconductor technology andinductive components have boosted the use of compact, high

efficiency power supplies of the switch -mode type. Now SMPSs ofvarious power ratings are becoming widely available at

reasonable prices, it seems timely to focus on their designprinciples and practical aspects.

Most electronic circuits can notwork without a power supply ofsome kind. The basic mainssupply consists of a trans-former, a rectifier, a filter(smoothing/reservoir capaci-tor), and a linear control circuit(regulator) for adjusting the out-put voltage to the desired value.It may be argued that the basicpower supply has a number ofimportant disadvantages. Forrelatively high powers, themains transformer is oftenbulky and expensive, and thesame goes for the smoothingcapacitor(s). Moreover, theproduct of the voltage dropacross the regulator and thecurrent consumption of theload forms dissipated, andtherefore wasted, power. whichresults in a very low overall ef-

Fig. 1 The 3 basic configur-ations of a switch -mode powersupply.

ficiency, especially at relativelylow output voltages. Not sur-prisingly, in the rapidly ex-panding world of microelec-tronics there arose a growingneed for a high -efficiencypower supply.This need was met by theswitch -mode power supply(SMPS), in which the outputpower is not regulated continu-ously, but pulsed at a relativelyhigh frequency. An output filteris included for smoothing thesupply voltage.The filter components can bekept small thanks to the highfrequency, and the same goesfor the (toroidal) transformer if

Basic configurationsA switch -mode power supply isessentially a DC -DC converter.The 3 basic circuit configur-ations are shown in Fig. I. Theflyback circuit works asfollows. A magnetic field buildsup in the inductor as long as theswitch remains closed. Whenthe switch is opened, the induc-tor functions as an energysource. The voltage across theinductor is reversed, and theconducting diode passes theenergy to the reservoir capaci-tor. Note that the output voltageis reversed with respect to theinput voltage.The forward converter doesnot reverse the polarity of theinput voltage. The capacitor ischarged via the inductor whenthe switch is closed. The differ-ence between the input and theoutput voltage is available onthe inductor. In contrast to thatin the flyback converter, theswitch is closed when the ca-pacitor is being charged. Whenthe switch is opened, the mag-netic field of the inductor isweakened via the flybackdiode. The switch is, of course,a power transistor, and the di-

ode affords protection againstthe induced voltage. In a for-ward converter, the input volt-age is higher than the outputvoltage.The third basic configuration isreferred to as boost or step upconverter. This circuit in-creases the input voltage, and isfunctionally similar to theflyback converter. Energy isstored in the inductor when theswitch is closed. When theswitch is opened, this energy issupplied to the load at the out-put via the diode.

The continuous anddiscontinuous modeTwo modes of operation can bedistinguished, depending onthe current in the inductor-seeFig. 2.After closing the switch, thecurrent in the inductor in-creases linearly up to a specificmaximum value (IL = constant).After opening the switch, thecurrent decreases linearly. The

circuit operates in the discon-tinuous current mode if the cur-rent is nought in every period.The capacitor supplies the loadcurrent during the remainder ofthe period. The discontinuousmode is characterized by thegood response of the closedregulation circuit to fluctuationsin the input voltage (line regu-lation), and the output load(load reaulation). There is noenergy in the inductor at thestart of each period, and regu-lation can, therefore, take placeon a period -to -period basis. Itcan, in fact, be argued that theinductor is not present in theregulator circuit. The maximumphase shift of 90° in the buffercapacitor ensures the stabilityof the closed regulation circuit.A disadvantage of the discon-tinuous mode is the relativelyhigh peak current carried bythe power switch. Flyback andstep up converters usuallyoperate in the discontinuousmode.In the continuous current

Fig. 2 The discontinuous (a) and the continous current mode (b) dif-fer in respect of the current carried by the inductor.

EE

October 198750

Fig. 3 A traditional soft iron core (background) and aferrite core of equal power rating.

mode, the current through theinductor does not drop tonought at the end of everyperiod. The ripple current inthe inductor is small relative tothe load current, and this re-quires a fairly high self-inductance. The buffer capaci-tor, on the other hand, can bekept relatively small. Thefavourable shape factor of thecurrent through the power tran-sistor and the diode makes thecontinuous mode eminentlysuitable for high power appli-cations. The response to loadfluctuations is, however, worsethan that of a circuit in thediscontinuous mode. Eachchange in the output load cur-rent requires a correspondingchange in the direct currentthrough the (relatively large)self-inductance, and this pro-cess may take several periodsto complete.It is not possible for a system toautomatically switch from con-tinuous to discontinuous oper-ation, or vice versa, becausethis would cause a con-siderable change in the openloop transfer characteristics,giving rise to instability of theclosed regulation system. Thismeans that the load current of asystem in the continuous modeshould be higher than half thepeak -to -peak value of the ripplecurrent in the inductor. Forwardconverters usually operate inthe continuous current mode.

Off-line operationIn many cases, the input voltageis a rectified and smoothed

modern ETD

voltage obtained direct fromthe mains. The direct voltage soobtained (approx. 335 V at a240 VAC mains supply) is rarelyused for converting down to,say, 12 V, in view of the resultantlow duty factor, and the needfor large self -inductances. Also,a direct connection to themains is dangerous, and nor-mally not permitted. This callsfor a (ferrite) transformer,which, in an SMPS, has the ad-vantage of being much smallerthan a soft iron type used in thetraditional 50 Hz mains supply(see Fig. 3). There are, however,a number of important con-siderations as to keeping thelosses of the core materialwithin acceptable limits. Ferriteis used instead of laminatediron, and offers a number of ad-vantages. The construction of aferrite core is relatively simple,and ferrite is a light and in-sulating material.The turns ratio of the ferritetransformer enables convertingthe high input voltage down to avalue close to the desired out-put voltage. The conversion in-creases the duty factor, andhence reduces peak currents inthe power transistors.

Transformer circuitsThe simplest configuration ofan SMPS is the single transistorflyback converter shown in Fig.4a. This circuit is well-known inlow power supplies with an out-put rating up to about 250 W. Inthis application, the transformeris more properly referred to asa coupled self-inductance,

because it assumes the functionof the inductor shown in Fig. la.The forward converter in con-tinuous mode is more suitablefor feeding relatively heavyloads. The most commonlyfound version is based on asingle transistor and ademagnetization winding in theprimary circuit-see Fig. 4b.The transistor must be able tohandle twice the input voltage.The demagnetization windingcan be omitted if the circuit isextended with a transistor and aflyback diode as shown in Fig.4c. In this circuit, the transistorsneed only withstand half thevoltage. They are, however,driven with respect to differentpotentials, just as in the bridgecircuits to be discussed.Half or full bridge circuits areused mainly for high power ap-plications. The full bridgevariant is suitable for very heavyloads thanks to the fact thatthe effective input voltage isdoubled. The last variant,shown in Fig. 4g, is also abridge circuit, based on acentre -tapped transformer thatenables the transistors to be

driven with respect to a com-mon reference potential.Bipolar transistors as well aspower FETs can be used in theprimary circuit. Bipolar tech-nology is suitable for switchingfrequencies up to 50 or 100 kHz.Power FETs are faster, and canbe used at higher frequencieswithout running into excessiveswitch losses. Currently, themaximum usable frequency isabout 1 MHz, and power FETsare expected to becomepredominant in SMPSs in viewof the ever increasing switchingfrequencies. Power FETs forrelatively high voltages are,however, still quite expensive,and more attractive for use incountries with a 117 V mainssupply, such as the USA.

Core saturationAny transformer winding formsa self-inductance, and theaverage voltage across itshould, therefore, be nought.When this is not so, the remain-ing direct voltage causes an lin-early increasing direct currentuntil the core is saturated. The

Fig. 4 Various configurations of the switching power stage in anSMPS.

1111 EE

October 1987

Fig. 5 Functional diagram of a SMPS with the control electronicslocated at the secondary side la) or the primary side (b).

H -field, and with it the current,then increases exponentially, inaccordance with Faraday's lawof constant increase of the mag-netic flux per unit of time. Thiseffect must be preventedbecause it can lead to destruc-tion of the primary circuit.In the circuits of Fig. 4b and 4c,the field in the transformer coreis weakened with the aid of theflyback diode(s), but only aslong as the duty factor remainsbelow 50%. Problems owing topermanent magnetization arenot expected to arise in the cir-cuit of Fig. 4d, where the coup-ling capacitor ensures theabsence of direct currentthrough the primary winding.The situation is more complexin Fig. 4e.Although the primarywinding is AC coupled, a directvoltage may still exist at thejunction of the capacitors. Thispositive or negative potentialmay arise from less than perfect(i.e., unbalanced) driving of thepower transistors, which mayhave different recovery timesalso. Unbalancing of theprimary circuit can beprevented with the aid of a com-pensation winding and 2 fly-back diodes.A coupling capacitor forblocking the magnetizing

direct current is rarely used inthe circuit of Fig. 4f. becausethis is rated for very highpower. Both the positive andthe negative current in theprimary winding are measured,and any difference betweenthem is compensated by con-trolling the duty factor. Thissafety measure can be appliedto the circuit of Fig. 4g also.

Voltage controlIn a switch -mode power supply,the output voltage is measured,compared to a reference, andkept constant by controlling theduty factor of the drive signalapplied to the power switches(i.e., transistors). The regulatingeffect of the control circuitdepends on the open -loopcharacteristics of the system.The simplicity of the flybackconverter makes it less suitablefor many purposes, since theduty factor depends primarilyon the load at a constant outputvoltage. Good voltage regu-lation requires a high amplifi-cation of the measuring andcontrol circuit. In a forwardconverter, the voltage controlcircuit need not have a stronglyregulating effect because inessence the output voltage

depends only on the turns ratioof the transformer (assuming aconstant input voltage).There are 3 basic types ofvoltage control system: Direct duty factor control.

The error signal is amplified,and drives a pulsewidth modu-lator, which in turn adjusts theduty factor as required. A highoverall amplification is needed,at the cost of some stability-notably in the case of con-verters operating in the con-tinuous mode. Voltage feedforward. This is

the most commonly usedsystem. Preregulation of theduty factor is implemented as afunction of the input voltage,enabling the output voltage ofthe open loop system to bemade independent of the inputvoltage. The control circuit is,therefore, only required forcompensating load fluctuations.The preregulation system im-proves the line regulation, andso ensures sufficient suppres-sion of hum. Current mode control. A sec-

ond control circuit (innerloop) inside the voltage controlcircuit (outer loop) enablesswitching off the power transis-tor at a more or less fixed peakvalue of the current. The effectso obtained is the (quasi) disap-pearance of the inductor fromthe output filter. The wholesystem is then essentially a firstorder network with the capaci-tor in the output filter as theonly phase changing element.The stability of the wholesupply, as well as the responseof the closed system to fluctu-ations in the input voltage and

the load current, is excellent.High power forward convertersof the continuous type are oftenequipped with a current modecontrol for obvious reasons.

Location of thecontrol circuitThe voltage control circuit canbe located at the primary or thesecondary side of the supply. Acircuit at the primary side (Fig.5b) makes it possible to drivethe power stage direct from theIC, while it is a relatively simplematter to implement circuits forprimary current monitoring andpreregulation. A disadvantageof the primary location is theneed for an insulating device inthe control loop for transmittingan analogue signal from theprimary to the secondary side.This is usually done with the aidof an optocoupler. Only the er-ror signal is transmitted to ruleout instability of the outputvoltage owing to ageing effectsin the optocoupler.A control circuit at the second-ary side (Fig. 5a) enables directcoupling of the voltage controlcircuit. Also, it allows the use ofthe the reference circuit builtinto many of the currentlyavailable integrated SMPS con-trollers. The PWM signal is fedto the power stage via a fast op-tocoupler, or a special pulsetransformer. Differences in thedrive applied to several powertransistors are relatively simpleto monitor and correct, but theprimary location makes it diffi-cult to keep tabs on the primarycurrent.

6 C $1.. 1.1,n Ua IstatiCired)

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Fig. 6 General block diagram of an integrated SMPS controller.

EE

October 1987

Whatever control circuit isused, it must have its own (start)supply. The self -generatedvoltage is, of course, onlyusable after the supply is fullyoperational.

SMPS controllersA wide variety of integrated cir-cuits is currently available forcontrolling switch -mode powersupplies. These ICs are essen-tially very similar, and a generalblock diagram is thereforegiven in Fig. 6 to explain theiroperation.The pulsewidth modulator iscomposed of a sawtooth gener-ator, a voltage comparator and aset -reset bistable. A second in-put on the comparator is con-nected to the output of anopamp that amplifies the differ-ence between the real and therequired (set) output voltage.An accurate, and temperaturecompensated, voltage refer-ence is often included for ad-justing a specific outputvoltage.The remainder of the circuits inthe chip have auxiliary func-tions, and serve for varioustypes of protection. Voltagefeedfonvard or current modecontrol is possible by changingthe slope of the sawtooth signal.Special control inputs make itpossible to set a duty factor ofnought. An analogue input isactivated above a predefinedvoltage level, and can be usedfor making a 2 -level short-circuit protection. When theoutput current reaches the firstlevel, the duty factor is heldconstant, and the circuit sup-plies a constant, maximum, cur-rent. The duty factor is madenought above level 2. A digitalinput enables remote control ofthe supply (computer -controlled test sites, etc.).An input for setting the maxi-mum duty factor is standard onmost SMPS controllers. Prop-erly driven, it prevents satu-ration of the transformer core,and hence an exponentially ris-ing primary current. This safetymeasure is especially useful forsupplies operating in the con-tinuous current mode. In these,the duty factor has a tendencyto rise to the maximum value ateach change in the output cur-rent, in an effort to correct thedirect current through the in-ductor in the output filter in ac-cordance with the new load.

7

1.59:2W-1--i

B 250C 700

1pF220V

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220V-100!!

OC

R, a

2x220AF350 \r'.2C,

B 250C 3000

1800

BY 28911000

1'1

n2201122W

150pF630V T

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2.2 k!!- BUZ 80 2125

40,9 B

101(1!

coR, I

II

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820 pF

i

HIRT12kfiI-16

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1 nF

Hi330 nF

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U W 2 4.71.11!--1_1

01

R7 02TDA 4718

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13

Li, WOW,ISYN OSYN

100

2.2k!!

4.7 k1.1

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CNY 17.2

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1,.2 i4.7nFBYS 28 lsonH

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controlboard

15

18 ki/

zs 12 VAIN 22°PFI16V

L

14

12 kiin

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1

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4

220 HD 2.2 kf tn

loonFl- L471(111-11

3.0V

87131-7

O

0O

Fig. 7 Circuit diagram of a 5 V; 20 A; 50 kHz supply !courtesy Siemens).

The multi -voltagesupplyAdditional supply voltages arefairly simple to implement in aSMPS with the aid of appro-priate auxiliary windings on thesecondary of the transformer.In computer equipment, theusual combination is a powerful5 V section, and auxiliary +12 Vsupplies. Voltage control isusually only effected on the+5 V rail. If the magnetic coup-ling between the secondarywindings on the transformer issufficiently tight-this is typicalof a well -constructed trans-former-the output voltage ofthe auxiliary windings isregulated along with the mainsupply, at acceptable accuracy.

LossesSwitch -mode power suppliesare known mainly for their highefficiency. In spite of this, somepower is, of course, wasted.

Switching losses in thepower transistors. Faster

switching-e.g. with the aid of aspeed-up capacitor-keepsthese losses acceptable. Thepower loss incurred in the con-ductive transistor is relativelysmall, especially at high inputvoltages. Transformer losses can be

classified as copper or corelosses. At switching fre-quencies below 100 kHz, cop-per losses are the mainconsideration in finding the op-timum specifications of the

transformer in the SMPS. Also,care should be taken to countera considerable skin effect,which reduces the effectivediameter of the copper wire asthe frequency increases. ManySNIPS manufacturers use litzewire for their transformers toprevent losses arising from theskin effect.

Core losses are due to eddycurrents and hysteresis of theferrite material. They dependon the so-called flux densitysweep, and the frequency.Manufacturers of ferrite corescan supply graphs to establishthe maximum permissible corelosses as a function of the ther-mal resistance of the core. andother parameters. Core losses

EE

October 1987

form the crux in designing atransformer for use in an SMPS. Rectification and filter losses.These become more serious atrelatively low output voltages(5 V), and are mainly due to theforward voltage drop across thediodes. Schottky diodes areoften used in view of their lowforward voltage drop and goodswitching characteristics. Somepower is also wasted in the in-ductor as part of the outputfilter.

A practical circuitThe circuit diagram of a typicalswitch -mode power supply isshown in Fig. 7 (Siemens Appli-cation).Buffer capacitor Ci is fitted atthe output of a bridge rectifier,which is fed from a mains filter.Power resistor limits thepeak charge current when thesupply is switched on. The typeof transformer used makesclear that the circuit is a for-ward converter. The primaryand secondary winding (N2; Ns)are in phase, as indicated by thedots. Auxiliary windings NI andN3 serve to demagnetize thecore. The dotted line in the coreindicates the use of an elec-tromagnetic shield. The con-figuration of the secondaryoutput filter shows that thesupply is designed for oper-ation in the discontinuous cur-rent mode. A relatively smallself-inductance is used in con-junction with a large buffercapacitance to ensure sufficientoutput power when the induc-tor carries no current. The out-put voltage is divided andcompared to a 3 V reference.The error signal from the oper-ational amplifier is fed to theTDA4718-based primary controlcircuit via an optocoupler.Components Cr and RT definethe switching frequency of50 kHz. Provision has beenmade to set the maximum out-put current (pin 9). The maxi-mum primary current ismonitored with the aid of thenetwork connected to pin 8.The capacitor fitted at pin 15 ofthe controller ensures a gradualincrease of the duty factor afterpower -on (soft start). The inputvoltage is checked via pin 6 and7. The duty factor is madenought when the input voltageis either too low or too high.Voltage feedfonvard is im-plemented with the aid of RR,connected to pin 2. The switch

Fig. 8 A compact switch -mode power supply.

signal at the output of the con-troller is fed to the powerMOSFET via a number of paral-lel CMOS buffers contained in aCD4049 package. The controlcircuit is fed from the mains viaa capacitive voltage divider.Figure 8 shows a compact SMPSfitted on a printed circuit board.The arrows point to the follow-ing, essential, parts: (1) mainsfilter; (2) primary rectifier; (3)buffer capacitor for primaryvoltage; (4) switching transistor;(5) pulse transformer for basedrive; (6) SMPS controller forpulsewidth modulation; (7) (sec-ondary) voltage reference anderror amplifier; (8) ferrite coretransformer; (9) primary flybackdiode for weakening the trans-former field; (10) inductor inoutput filter; (11) secondary rec-tifier and flyback diode; (12)output capacitor.

Further developmentsThe scope of this introductoryarticle does not allow a detaileddiscussion of all the technicalconsiderations that go intodesigning a switch -modepower supply. In a forthcomingissue of Elektor Electronics thesubject will be reverted to inthe context of a constructionproject.The theoretical aspects of theSMPS have been known forsome time, but it was not untilthe coming of fast power tran-

sistors, integrated controllersand new ferrite materials thatserious development of theSMPS was launched. Everhigher switching frequenciesmake it possible to reduce thesize of the secondary filter, butat the same time pose a real dif-ficulty as regards elec-tromagnetic interference (EMI)due to the often large numberof strong harmonics and otherspurious products. It is with thisin mind that there is a growinginterest in free -running sup-plies, in which the currents aresinusoidal rather than rec-tangular. Meanwhile, suppliesof the types discussed in thisarticle are constantly reworkedand enhanced to make the cur-rent consumption from themains sinusoidal. This ensuresless interference on the mains,a higher efficiency of the recti-fier thanks to the morefavourable shape factor of thecurrent, and reduced peak cur-rents in the buffer capacitor(s).

TW

For further reading:

High frequency powertransformer and chokedesign. Part 1...4 incl.;Philips Technical publi-cation, September 1982.

Electronic Components &Applications. Vol. 2; No. 1;Philips, November 1979.

Unitrode SwitchingRegulated Power SupplyDesign Seminar Manual;Unitrode, ed. 1986.

Schaltnetztelle (SNT),Techmk und Bauelemente;Siemens Technische Mit-teilung No. B9 -B3269.

Steuer und Uber-wachungsschaltungen fuermoderne Schaltnetzteile (SNT)TDA47xr Familie; SiemensTechnische Beschreibung No.B/3132. Integrierte Schaltnetzteil-Steuerschaltungen, Funktionund Anwendung; SiemensTechnische Beschreibung No.BI -B3116.

SGS power supply appli-cation manual; July 1985. Various databooks and ap-plication notes: Intersil;Mullard; SGS; Siemens; Thom-son; Unitrode.

EE

October 198754

THE POSITIVEIMPEDANCE CONVERTER

by A.B. Bradshaw

One of the very practical means of simulating inductance inelectrical circuits is by the use of gyrators. The positive im-

pedance converter is a member of this family. Its main use is toreplace wound inductors in AF circuits, particularly where these

have large values, or to simulate coils at very low frequencies.

The positive impedance con-verter makes use of operationalamplifiers: two are needed tosimulate a grounded inductor;four are required to simulate abalanced inductor. But onlyfour opamps are needed tosimulate a node, containingbalanced and grounded induc-tors, as will be shown later.Where simulation of groundedinductors is used, the opampsshould be operated frombalanced power supplies.The writer has used the PIC asa circuit element for a numberof years in the design of high-performance AF filters. The Qvalues obtained with thesedevices is very much higherthan that of the wound equiv-alent. Instability problems arerare. Although the frequencyresponse of the opamps usuallylimits the operating range ofPICs to about 40 kHz, this is ad-equate for most AF and even anumber of data filtering re-quirements.The circuit diagram of a typicalPIC is shown in Fig. 1. The inputimpedance of this circuit ap-pears as a pure inductancewhen the output is groundedthrough Ro. Resistors RI, R2and R3, as well as capacitor C

are normally 1% types. ResistorR0 is used as the inductancesetting component.

The general symbol of a PIC isshown in Fig. 2, but in practicalcircuits, when used as a circuitelement, it is usually indicatedas in Fig. 3.

3

57154 - 3

Analysing the PICThe analysis of gyrators is nor-mally performed with the aid ofmatrix algebra and the formalnodal analysis of networktheory. The formal approachhas a lot to offer as regardsgenerality, but it sometimes .

tends to obscure the practicaloperation of the circuit.Because of this, the writer hasadopted an approach whichwill be familiar to most readers.Assuming that opamps areperfect, the analysis can be

simplified considerably. In anideal opamp, the voltage gain is infinite:

Aro=ce; the input resistance is in-finite: = co ;

the output resistance is zero:row= 0;

the bandwidth is infinite:BW = co;

there is zero input offsetvoltage: E. = 0 if EH/ = O.

Since the voltage gain is infinite,any output voltage is the resultof an infinitely small inputvoltage. In effect, therefore, thedifferential input voltage iszero.The preceding assumptions areused as axioms in the following.For the purposes of examiningthe operation of a PIC, it isredrawn in Fig. 4. Some of thevoltages and currents areshown twice to emphasize thecircuit action.

(141-V2)1R3 =I3

(111-174)1 R2= A

Eq. 1

Eq. 2

(1/1-114)1 R = 12 Eq. 3

Since the input resistance of theopamps is infinite. /0=0,whence

13=15

and

12=1m

From Eq. 3:

VI- V4 =R1.12

Dividing both sides by R2 gives

(V1-14)/ R2= Ili -1R /R2 Eq. 4

Since 13=15. Eq. 1 is equal toEq. 2, so that

(1/1- V2)/R3 = ( 174)1R2 =

IffiRi1R2 Eq. 5

To remove V2 from Eq. 5, con-sider the middle section ofFig. 4, which for convenience'ssake is reproduced in Fig. 5.

EE

October 1987

-V2= /4 =Jo) C

Also, since /0=0, /4/ VilRo

Combining these expressionsgives

V2= VilfioCRo Eq. 6

Dividing both sides of Eq. 6 byR3 gives

( V1- V2)/R3= //co CR0R3

in which the left-hand term isalso that of Eq. 5, whence

LnRi1R2=VtljoiCRoR3

from which V2 has beenremoved.

Cross multiplying this last ex-pression yields

VilLn=jwCRoRIR3/R2

Since VI= Vin,

Vinlbn=Zn=ju.(CRIR31R2)Ro

which is the expression for apure inductance in which

L=(CRIR3/R2)Ro

If K=CRiR31R2,

L=KRo

Kis called the conversion factorof the PIC.This completes the basicanalysis of the PIC without theneed of anything more thanelementary AC theory andalgebraic manipulation.

Practical applicationsThe numerical values of RI, R2,and R3 affect the signal hand-ling capabilities of practicalopamps and are, therefore, acompromise. Typical valuesare:

RI =270R 1%R2= 5k6 1%R3 =10 k 1%C=10 nF I% silver mica (two5000 pF types in parallel).

These values enable the com-putation of K:

K=CR,R31R2==270 x101 x10 x10-3/5.6 x103=

=4.8214x10-`

In practice, the author used anMC1458 operating from a +12 Vpower supply, which has aK=5.7155 x 10-6. The departurefrom the ideal K value is due tothe approximations used withthe opamps: this is not a realproblem in practice. The com-plete circuit of the PIC with thevalues stated is given in Fig. 6.

Checking the value ofK in practiceBuild the circuit of Fig. 6 andbring it to series resonancewith the aid of a test set-up as

7

counter

AFsignal

generator

tz, sr:zpert, ca,

cad zedx_e get.-steemtpat 2 to tow vat: e

PIC

8

Lt

0 0L, is simulated by PIC, + PIC, (Rai)L, is simulated by PIC 2 (R02)

0

shown in Fig. 7. If the generatorequivalent impedance is smalland C is known accurately, thefrequency, f, can be measured.Since

f=1/2n1 LeftC,

and

Leff=KRo

K can be found to 1-2% accu-racy once Ro is given.The conversion factor can betrimmed by small adjustmentsto R3.Inductances are simulated byPICs as shown in Fig.8, where(a) is grounded coil simulation;(b) is balanced coil simulation;and (c) is grounded and ba-lanced coil simulation. In (c), L1is simulated by PIC1 +PIC2(Rol), and L2 by PIC2(Ro2).In conclusion, the author wouldemphasize that the PIC is a veryuseful circuit element andshould not be left shrouded inmystery. It is hoped that thisarticle will help it find muchlarger appreciation and appli-cation.

NEW LITERATURE NEW LITERATUREModern OptoDevice Projectsby R.A. PenfoldISBN 0 85934 168 2104 pages - 178x110 mmPrice £2.95 (paperback)Not so long ago opto-electronicdevices were a rarity, virtuallyconfined to cathode-ray tubes,"magic -eye" tuning indicators,and some photoresistors. Overthe past ten to fifteen years,there has been a procession ofnew opto-electronic devices:light -emitting diodes, liquidcrystal displays, a variety ofphoto sensors, and many more.This book provides practicaldesigns incorporating optoelectronic devices, includingfibre optic devices, ultra brightLED's, and infra -red detectors.The designs should be withinthe capabilities of anyone with acertain amount of experienceof electronic construction: oneor two of the designs aresuitable for beginners.

Bernard Babani LimitedThe GrampiansShepherds Bush RoadLONDON W6 7NF

Automotiveelectronicsystemsby Trevor MellardISBN 0 434 91257 3156 pages - 245x190 mmPrice £9.95 (soft cover)Progress in the application ofelectronics to the automobilehas been rapid. It has createdproblems for the industry's ser-vice personnel, and bewilder-ment for the ordinary motoristwho no longer recognizes whatis under the bonnet and behindthe dashboard.To rise to the challenge offered,the service technician needs anunderstanding of electronicprinciples, technology, andpractices. This well -illustratedbook is designed to serve as apractical guide for qualifiedcraftsmen, technicians, andengineers who wish to keeptheir skills and knowledge up

to date, and for motorists andelectronic enthusiasts who areinterested in how the moderncar works. It will also be ofbenefit to students of a varietyof City & Guilds and BTECtechnician courses.The author teaches automotiveelectronics at West GlamorganInstitute of Higher Education,Swansea, where he is Head ofthe School of AutomobileEngineering.

William Heinemann Ltd22 Bedford SquareLONDON WC1B 3HH

BS 5942:Part 2: 1987IEC 581-2: 1986High fidelity audio equipmentand systems; minimum per-formance requirementsSpecification for FM radiotunersThis part gives the perform-ance requirements for FM radiotuner units, designed for thereception of frequency modu-lated sound broadcast emis-sions and primarily intendedfor high -quality reproducingsystems for home use. Re-ceivers (tuner -amplifiers) aredealt with in Part 8.British Standards are availablefrom

British Standards Institution2 Park StreetLONDON W1A 2BS

LoudspeakerDesignCookbookby Vance DickasonISSN 0 8338 0194 595 pages - 280x215 mmPrice £15.00 (soft cover)When the Loudspeaker DesignCookbook was first publishedin early 1977, it was among thefirst loudspeaker constructionbooks to show how to employthe relatively new box designtechnology developed byThiele and Small. It was also

one of the first to advocate loadlevelling circuitry forcrossovers. In those days, few

driver manufacturers couldsupply this type of information,much less understand it.Today, almost all manufacturersprovide rather detailed driverspecifications, and many caneven supply three-dimensionaltime -delay plots for their prod-ucts. This increase in infor-mation availability. plus theever -inflating price of qualityfinished loudspeakers makethe prospect of designing andbuilding your own loud-speakers an even more attract-ive hobby.In eight chapters, Mr Dickasoncovers all the basics for thebeginner, as well as a com-prehensive overview of the fac-tors that determine loud-speaker performance.In our view, this makes thebook a valuable reference toolfor the most sophisticated loud-speaker design enthusiast

Marshall -Jones Co.Old Colony SoundBox 243Peterborough NH 03458USAAvailable in the UK from:Falcon ElectronicsTabor HouseNorwich RoadMULBARTONNorfolk NR14 8JT

RADIO andELECTRONICSEngineer'sPocket Book17th Editionby Keith BrindleyISBN 0 434 90179 2201 pages - 195x92 mmPrice £6.95 (Hardback)That this 17th Edition is pub-lished a mere 18 months afterthe 16th is an indication of thepopularity of this invaluablecompendium of facts, figuresand formulas. This new editionhas been completely revisedand enlarged. The author hasincluded anything of relevanceto radio and electronics re-

ferred to in literature. A con-siderable amount of newmaterial relating to recentdevelopments in radio andelectronics has been added, in-cluding new sections on bat-teries, cables and connectors.All the broadcasting infor-mation has been updated. It isinteresting to note that the 17thEdition contains the new logicsymbols to BS 3939 (IEC 617-12),which we found sadly lackingin the 16th Edition (see ElektorElectronics, May 1986, p. 51).There is no doubt in our mindsthat this edition will prove to bejust as useful, popular, and in-dispensable to the student,designer, service engineer andanyone else interested in radioand electronics as itspredecessors.

William Heinemann LTD22 Bedford SquareLONDON WC1B 3HH

Power SelectorGuideby J.C.J. Van De VenISBN 0 85934 180 1160 pages - 172x128 mmPrice £4.95 (soft cover)This power selector guide isone of a new generation ofpocket guides published bijBernard Babani. It is compiledespecially for the electronicsdesigner, engineer, and hobby-ist. It is unique in the way thetabular data is presented invarious useful categories so asto aid easy selection of possibledevices.The use of the guide is two -fold.It could be used to select adevice for, say, a particulardesign application by refer-ence to the electrical character-istics, case type, etc. Or it couldbe used to choose a replace-ment or equivalent devicewhen a knowledge of theoriginal specification isavailable.

Bernard Babani LimitedThe GrampiansShepherds Bush RoadLONDON W6 7NF

EE

October 1987

NEW LITERATURE NEW LITERATURE

HUGHESELECTRICAL

TECHNOLOGY6th Editionby Edward Hughesrevised by Ian McKenzieSmithISBN 0 582 41372 9656 pages - 238x165 mmPrice £12.95 (soft cover)Edward Hughes' ElectricalTechnology has been the stan-dard text for students requiringan introduction to electrical andelectronic engineering formore than twenty-five years.This sixth edition, extensivelyrevised and updated by IanMcKenzie Smith. includesmuch new material on the fun-damentals of electronics. andreflects the changing re-quirements of today's courses.In particular, increased em-phasis has been placed on fun-damental semiconductordevices: for instance, field ef-fect transistors and operationalamplifiers have been added tothe junction transistorspreviously covered in the fifthedition. Chapters have alsobeen added to cover digitalsystems and an introduction tomicroprocessors and their pro-gramming.As in previous editions, the textis supported by a substantialnumber of worked examplesand problems drawn fromexamination papers.Providing unrivalled coverageof the basic concepts of thesubject, this book will continueto be the definitive work for allthose studying electrical enelectronic engineering fromtechnician level through to firstyear degree standard. It alsoprovides an exellent groundingfor students approaching thesubject from other engineeringdisciplines.All the diagrams in the workhave been redrawn to complywith current practice. Symbols,abbreviations and definitionsused are based on PD 5686:1972(BSI) and The InternationalSystem of Units (1970), preparedjointly by the National PhysicalLaboratory, UK, and theNational Bureau of Standards.

USA, and approved by the Inter-national Bureau of Weights andMeasures.Finally, this important work cannot possibly be rivalled at theprice.

Longman Scientific &TechnicalLongman HouseBurnt MillHARLOWEssex CM20 2JE

DesigningKnowledge-

based Systemsby T.R. AddisISBN 0 85038 859 7322 pages - 220x145 mmPrice £15.95 (hardback) £9.95(paperback)Designing a knowledge -basedsystem, sometimes referred toas Intelligent Knowledge -BasedSystem-IKBS-that uses a verylarge number of facts requirestechniques that are drawn fromdatabase theory computerscience, and artificial intel-ligence.Database theory has evolved tocope with the design of massstorage structures for multipleapplications. Artificial intelli-gence is concerned with thecomplex relationships of factsstored in main memory. Theissues within each of thesefields are strikingly different.Yet, both fields share the use ofthe computer for theirrealization.This book describes a methodfor managing the design oflarge-scale database systemsfor problems which may involvetechniques derived from ar-tificial intelligence. It is primar-ily intended for computerscience graduates who havespegialized in either databasetheory or artificial intelligenceand who would like to have anunderstanding of the relation-ships between these fields.

Kogan Page Limited120 Pentonvile RoadLONDON Ni 9JN

DesigningIntelligentSystemsby Igor AleksanderISBN 0 85038 860 0166 pages - 220x145 mmPrice £12.95 (Hardback)Until comparatively recently, ar-tificial intelligence was seen asthe concern of only the mostadvanced researchers in com-puter science. Now, largely dueto the falling costs of computersand silicon chips, the "intelli-gence" of information tech-nology equipment is continu-ally being increased in practi-cal terms. This book is an in-troduction to the design prin-ciples of such systems. It makesno assumption of prior knowl-edge of either computerscience or engineering and ismathematically self-contained.The book is based on a coursetaught by the author to first -yearstudents in engineering,management and psychology,may of whom had no priorknowledge of mathematics. Itis, therefore, of particular in-terest to practitioners, industrialsystem designers, teachers, andstudents of information tech-nology alike.

Kogan Page120 Pentonvile RoadLONDON N1 9JN

ApplicationsBook No. 4UHF/VHFGalliumArsenideTexas Instruments Publication80 pages - 210 x147mmThis booklet from Texas Instru-ments' West German TrainingCentre contains a general in-troduction into the operation ofGaAS FETs, applications of theTypes S3000 and S3030, reprintsof constructional articlesfeatured in VHF Communi-cations, and data sheets.

Since the early days of ;ran-sistorisation high frequency ap-

plications have been stimu-lating semiconductor tech-nology for all small signal appli-cations. For example, the firsttransistors which wereemployed on a large scale inTV receivers were germaniumIF amplifiers, as well as VHFand UHF Tuner devices.This was back in 1959/1960,when the Germanium Mesaprocess was the state-of-the-art,and it rapidly displaced thevacuum tubes by PNP tran-sistors, especially in UHF andVHF gain -controlled amplifiers.With the advent of Silicon andthe improved planar pro-cessing technology, the mostchallenging applications wereagain UHF amplifiers andmixers. PNP and NPN forward -gain -controlled amplifier tran-sistors dominated in TV andradio equipment in the early70's, until the growing radioand TV networks required animproved large -signal handlingperformance of RF front -ends.The two competing conceptswere:'.The superior cost/perform-ance features of the Si MOS-FETconcept quickly outdated thePIN concept.Now a new concept has beenrealised with Gallium -ArsenideSchottky -Gate FETs. The firstdevices are the Dual -Gate typesS3030 and 53000, which arecompatible to Si-MOS FEN inexisting circuits and systems,and can replace them with onlyminor changes.The improvement of the RFcharacteristics of the GaAsdevices is a step -function ratherthan a gradual improvement.This new GaAs-FET productiontechnology will not only enablethe development and pro-duction of RF ICs, but also trig-ger the wider use of GaAsdevices in digital and analogapplications, where theirspeed, higher operating tem-perature, lower saturationvoltages and higher efficiencycan be exploited.

Texas Instruments LimitedManton LaneBedford MK41 7PA.

EE

October 19874

RESEARCH COLLABORATIONTO BOOST INFORMATION

TECHNOLOGY

The fast moving world of infor-mation technology has wit-nessed two significant develop-ments recently in Britain. Muchcloser links have been forgedbetween research and productdevelopment, and plans havebeen made to exploit theresults more actively in theworld's markets.In 1981, Japan launched a tenyear national programme to de-velop what are known as fifthgeneration computer systems.This ambitious project aims tobring together all the necessaryelements of "clever" com-puters which, in the 1990s, willbe able to demonstrate artificialintelligence and simulatehuman hearing, speech andvision.Britain's response to theJapanese challenge was tomount its own five year pro-gramme of advanced ITresearch known as the AlveyProgramme. It started in 1983,and will cost eventually about£350 million, of which £200million will come from publicfunds and £150 million from par-ticipating companies.

Wide ranging studyThe programme consists of pre -competitive research projectswhich fit into national strategiesin key areas of technology. Theyinvolve collaboration betweenuniversities, industry andresearch establishments; andbetween different companieswithin industri.The Alvey Programme orig-inally aimed to cover four maintechnologies:* Very large scale integration

(VLSI) in integrated circuits.* Software engineering, the

development of standardmethods for writing computerprograms and systems.* The man/machine interface

by Kenneth Owen

(MMI), software and hard-ware aspects of making com-puters easier to use.* Intelligent knowledge based

systems (IKBS), exhibiting ar-tificial intelligence.Another topic, advanced com-puter architectures (overalldesign frameworks) has sincebeen added.In parallel with the Alvey Pro-gramme, a similar one wasstarted by the European Com-munity. This is known as theEuropean Programme of

Research and Development inInformation Technology(ESPRIT). Twelve majorEuropean electronics and com-puter companies played a keyrole in defining ESPRIT, includ-ing Britain's GEC, ICL andPlessey.Collaboration between com-panies and universities in dif-ferent countries is a feature ofthe ESPRIT research and devel-opment. The hope is that it willeventually lead to Europe -widemarket exploitation.

Claimed as the world's first computer on a chip, thetransputer, developed in Britain, combines the functions ofprocessing, storage and communications. It can be used either as aconventional microprocessor or in multiple transputer systems toprovide extremely powerful supercomputers.

INMOS

Innovative productsSo British IT firms' ownresearch and development ac-tivity has three elements: Alveyprojects, ESPRIT projects, andindividual in-house work.Together, these variouselements have strengthenedthe industry's research baseand the projects are leading toinnovative products, systemsand services in areas of key im-portance for the future. Theyreflect an important feature ofthe information technologybusiness: the predicted con-vergence of different tech-nologies, computers, communi-cations and so on into inte-grated systems. This has hap-pened much more rapidly thanmany people expected.The new IT techniques, prod-ucts and processes are beingapplied throughout the manu-facturing and service industriesto automate existing functionsand introduce new servicesand facilities that were once im-possible.An ingenious British IT inven-tion now being applied inpowerful systems is the INMOStransputer, a computer on achip. A single one can be usedas a high performance conven-tional microprocessor. Evenmore significantly, groups ofthem can be used in multipletransputer systems to provideextremely powerful supercom-puters.

All involvedPlanning for the exploitation ofproducts and systems in theworld's markets forms part ofBritain's national IT effort thatwill follow the Alvey Pro-gramme. The aim is to stimulatethe development and use of ad-vanced IT systems, and so willinvolve both producers andoperators in addition to theacademic research sector.(LPS)

1

THE DESK -TOP SUPERCOMPUTERby Staniforth Webb

Modular concepts of computer structure using large numbers oftransputers, each as powerful as a mainframe installation, arebringing the vast computing power so far used only for such

applications as meteorology or high-technology design down tothe domain of the desk -top device. They will cut computing costs

by some 90 per cent.Electronics engineers atSouthampton University plan tounveil a supercomputer thisyear to match the most powerfulmachines now in service, butwhich could be produced andsold at about only one -tenth oftheir price. Designed by DrChris Jesshope and Dr DenisNicole in the University's De-partment of Electronic Engin-eering, it has been developedas part of the ESPRIT pro-gramme, the European initiativeat government level which aimsto keep advanced technologyin Western Europe well abreastof that in other countries.The main reason for the lowcost of the Southampton com-puter is that it is built on amodular principle. It isassembled from 350 so-calledtransputers, each of which is acomplete computer in minia-ture with its own memory andan appropriate set of connec-tions to link it to othertransputers or to other com-puters, all on a single siliconchip of about 100-mma area.This contrasts with the designof the Cray supercomputer, forexample, which is composed offour linked mainframe com-puters.Transputers sell at about $500apiece. A commercial com-puter built on the Southamptondesign could be sold foraround $800 000; a Cray costssomewhere in the region of $6million.So far, such enormously power-ful computers are used in only afew specialised applicationssuch as weather forecasting,aircraft design and some areasof scientific research. But re-ducing the cost of supercom-puting power by a factor of 10would obviously open up farmore applications and bringsupercomputing power withinthe reach of many more poten-tial users. In the words of ChrisJesshope, "It could put yester-day's supercomputer ontoday's posh office desk."

Mainframe PowerThe transputer has beendeveloped and is beingmarketed by the British siliconchip company INMOS. Eachcarries a processor that can beprogrammed to perform vari-ous tasks, a memory that con-tains a large part of theinformation the processorneeds for its job, and all theconnections for linking intoother devices.A single transputer is as power-ful as an average full-sizedmainframe computer. It is ableto perform one -and -a -halfmillion operations every sec-ond. Its circuitry is as complexas a complete street map ofLondon with all the gas mains,

cables and sewerssuperimposed. It works fasterthan comparable processors, iseasier to programme and ismore compact. But from thepoint of view of assembly intosupercomputers. its most im-portant advantage is the easewith which it can be linked toother transputers or to othercomputers with no need for ex-tra electronic circuitry.Because of the Southamptonproject's significance for thefuture of the company, INMOSsupplied the University with thefirst of a new generation oftransputers, the IMS T 800. This

model can handle decimalpoints or fractions as well as in-tegers; it is the first micropro-cessor to incorporate afloating-point processorcapable of dealing rapidly withdecimal digits on the samepiece of silicon as a conven-tional processor handling in-tegers.In technical language, the IMST 800 includes a 32 -bit integerprocessor which is the world'sfastest, with special instructionsto support graphics operations,a 64 -bit floating-point pro-cessor, four kilobytes of fast on -chip RAM and four standard IN-MOS communications links, allon a single chip.As Peter Cavill, Director of theINMOS Microcomputer Prod-ucts Division says, "Incor-porating all this on the samechip significantly increases itsperformance, by eliminating allthe delays associated withmulti -chip solutions. The resultis higher reliability. reducedboard space and lower overallsystem costs, as well as beingconsiderably faster."

DevelopmentPotentialJesshope and Hey see no prob-lems in linking as many as 1000

The basic transputer (T) is incorporated into a pool to make up a'supernode', which in turn is linked into an array to give amultistage switch with hierachical control.

transputers into a single com-puter. Beyond that, radicalredesign will be needed be-cause of the complexities ofcommunication between somany modules. But there isclearly a vast amount of devel-opment potential in the presentdesign.The cost of the transputer isconfidently expected to comedown as European companiesnow begin to make it a mainstayof their bid for sales in newareas. The Southampton projectis being backed by two Frenchcompanies as well as by the UKRoyal Signals and RadarResearch Laboratory. Half of thedevelopment costs have beenborn by the ESPRIT pro-granirne. French and Britishcompanies (TELMET andThorn -EMI) are expected tobuild computers based on theSouthampton design. Whenthese and the transputers theyincorporate come into wide useand their cost advantages I,-come apparent, it is predierthat large sales will reducetransputer prices still further.Because of their ability to workco-operatively in parallel on anumber of different but relatedtasks, transputers are wellsuited for use in so-called paral-lel processing. By designingcomputers which work on anumber of tasks simultaneously,instead of doing everything insequence, designers aim tomimic more closely the work-ings of the human brain.Transputers are also beingassigned to less futuristic appli-cations, including desk topsupercomputers, laser printersand what have been nicknamedturbochargers where thetransputer is used as an add-onunit to an existing system toupgrade its performance. High-performance graphics, engin-eering workstations androbotics are other areas wherethe transputer is already begin-ning to make an impact.

EE

October 198760

BACKGROUND TO HOLLOWEMITTER TECHNOLOGY

by Sue Cain and Ray Ambrose*

Hollow emitter technology falls into the area of power transistortechnology lying between bipolar and power mos, providing an

economic solution to high voltage switching. Ideally suited toswitching frequencies which cause problems to both bipolar and

power mos devices, hollow emitter technology improves theperformance of multiepitaxial mesa power transistors. This article

describes the features of hollow emitter technology, and discussesthe characteristics of some currently available devices.

Within the field of power tran-sistor technology, the area be-tween bipolar and power mosis occupied by high voltageswitching. An economicsolution is provided by hollowemitter technology.Hollow emitter technology isideally suited to switching fre-quencies which cause prob-lems to bipolar and power mosdevices. Products such as SGS'sFastswitch range provide rug-ged operation at very highswitching speeds, and highlevels of efficiency which allowmore compact designs withsmaller heatsinks.When compared to industrystandard high voltage devices,hollow emitter types providefaster switching times and alower saturation voltage. Theterm 'hollow emitter' refers tothe missing centre region in theemitter area, which reduces the

charge crowding effect at thispoint, as well as the storagetime required to remove the ex-cess charge.A thinner intermediate N layer,present with hollow emitterdevices, reduces the collectorresistivity and the saturationvoltage.

Standard versushollow emittertechnologyHollow emitter technology hasdeveloped out of the standardhigh voltage multiepitaxialmesa technology, the main dif-ference being that, with thenew technology, the emitter isnot diffused over the normalarea but only on the normalemitter edge.This difference has been im-plemented to overcome the

charge -crowding effect in thecentre of the emitter during theoff transition found in industry -standard high voltage devices.The result is much fasterswitching times.

Standard high voltageDuring the ON transition, thecharge in any normal highvoltage device is easily built upon the edge of the emitter. Atthe same time, the increase inbase resistance towards thecentre of the emitter reducesthe charge level at the device'scentre.While undergoing the OFFtransition, the base extractioncurrent of the device can rap-idly eliminate the charge at theedge of the emitter, but thecharge at the centre is removedwith some difficulty owing to

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the transversely distributed re-sistance in the base under theemitter finger.While the edge is turned off, anamount of charge remains at thecentre of the emitter diffusionwhich deceletates turn-off time.These conditions are illustratedat Figures 2a and 2b.

Hollow emitterIn the case of transistors such asthe SGS Fastswitch range, dif-fusion at the centre of the emit-ter is prevented by masking, asappropriate. The resultinghollow in the emitter preventsthe accumulation of chargesthat would slow down the turn-off time.Removal of the central region,with consequent reduction ofthe emitter area has a negli-gible effect on VcEsat. Thereare two reasons for this: first,the centre region of the stan-dard device carries lesscharge, and second, the in-termediate N layer is thinner,reducing the resistivity of thecollector, producing a fastswitching, highly efficientdevice.

Comparison ofswitching timesComparison of a standardmultiepitaxial mesa device witha hollow emitter device of the

EE

October 1987

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same dimensions and similarstatic characteristics gives aclear indication of the advan-tages provided by the latter.The fall time of the hollow emit-ter device is clearly superior tothat of the standard device,while storage time is alsoslightly better. Figure 3 com-pares the switching character-istic curves for two typicaldevices, the BUX48 standardmultiepitaxial mesa device, andthe SGSD00032 hollow emitter,showing that with resistiveloads the results produced bythe hollow emitter are betterthan those for the standarddevice over a wide range of col-lector current.Shorter fall and storage timesautomatically give rise to re-duced dissipation energy whilethe device is turned off.Furthermore, both base andemitter switching times arealmost always equally low in thecase of hollow emitter devices.For example, the SGSD00035tfroi is 5Ons for both switchingconditions.

Reverse bias safeoperating area(RBSOA)Figure 4 compares two com-parable devices, from the stan-dard and the hollow emittertechnologies, comparing theirreverse bias safe operatingareas. Although the RBSOAcharacteristic curves are betterfor the standard device at 400V,the hollow emitter device hasbeen optimised to give an im-proved RBSOA at highervoltages to suit switch modepower supply applications.It can be readily demonstratedthat the hollow emitter device

gives more protection at highervoltages, and this is balanced byadequate protection in areas oflower voltage and high current.

ApplicationsHollow emitter technology hasbeen devised in order to pro-duce devices with extremelyshort switching times asregards their high voltage andcurrent capabilities. As a result,hollow emitter devices arehighly efficient, and aretherefore well suited for appli-cations demanding fastswitching without high energyconsumption.Typical applications are thosewhich require the use of in-verters, switching regulators,fluorescent lighting and deflec-tion circuits with high definitiondisplays.

'Sue Cain is with BA Electronicsand Ray Ambrose with SGS

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EE

October 198762

TECHNOLOGISTS LOOK TOBRITAIN IN EUROPE'S GREAT

EUREKA PROJECT

Right up until 1985 "Eureka", asevery schoolboy knew it, wasthe cry uttered at one of themost famous moments in scien-tific history. It was when theancient Greek mathematician,Archimedes, arrived at an im-portant insight in the bathtub.The summer before last. how-ever, the word was prised out ofhazily recollected scientificfolklore, dusted off and ham-mered into shape as the gleam-ing new acronym encircling thenewly formed European Re-search Coordinating Agency.The idea behind Eureka. re-putedly first voiced by JacquesAttail, international economicadviser to President Mitterrandof France. was engendered bygrowing fears that Europe waslagging behind the UnitedStates of America and Japan inthe highly competitive worldmarket for high technology.The French answer was to pro-pose a concerted civilianresearch effort involving collab-oration instead of competitionbetween Europe's leading -edge technologists.Observers were sceptical atfirst about the chances of a pro-ject that was being billed as a"technological renaissance ofEurope" even before its aimsand methods had been agreed.However, little doubt now re-mains that a renaissance of sortsis underway.

Accident free carsDecisions made in Stockholmby ministers from 19 Europeancountries late last year broughtthe amount of money commit-ted to research projects carry-ing a Eureka label to over £2000million, with 37 new projectsgiven the ministerial stamp ofapproval and making a total of109 to date. These range fromplans to develop an intelligentaccident -avoiding car by themiddle of the next decade, to ascheme that could put diagnos-tic kits for venereal disease into

by Alisdair Stirling

doctors' surgeries the worldover by 1990.The latter is actually one of thesmallest projects, involving co-operation between two firms,one British and the otherSpanish. Some of the largerschemes may involve dozens ofparticipants spread around halfa dozen European countries.If critics were mystified at thealacrity with which Europeanindustry fell into line behindEureka's philosophy, they werepossibly even more surprisedby Britain's emergence as oneof its leading lights. However,the United Kingdom has nowbecome the driving force, asone European Community of-ficially conceded after theStockholm meeting.At the last count, 41 of the 109approved projects involvedBritish firms. This degree of in-volvement could cost the BritishGovernment some £39 millionover the first five years. How-ever, many of the 60 or so Britishfirms participating are small or

medium size, which particu-larly pleases the Departmentfor Industry and InformationTechnology which says it is re-ceiving at least 15 telephonecalls a day from companiesanxious to take part.British involvement extends intotwo of the biggest ventures. Theintelligent car, codenamed Pro-metheus, will involve co-operation between the UnitedKingdom and France, WestGermany, Italy and Sweden.The aim is to equip cars withsensors and microcomputersthat can spot danger early andavoid collisions by warning thedriver or by overriding his con-trols. The British input is fromBL Technology Ltd.

Clearer picturesResearch aimed at makingexisting telephone systems2000 times faster and forging avideo telephone system fromoptical fibre technology are thetwin concerns of Britain's

Recently acquired by Britain's Welding Institute is this 10 kWcarbon dioxide laser which can weld a steel component at up to1 m/min, ten times faster than conventional arc welding. Made inBritain, the laser is just one example of the sort of inventivenessthat has brought the United Kingdom into its important role amongthe Eureka nations.

Plessey PLC, in collaborationwith French and Italiancompanies. Also in the tele-communications field, threeelectronics specialists, ThornEMI, Mullard, and the Britishend of Philips, are combiningforces with French, WestGerman and Dutch firms to de-velop a high definition tele-vision transmission systemwhich will result in clearer pic-tures on screen.Running a finger down the list,salient examples of Britain's in-volvement abound. It is amonghalf a dozen nations involved inEureka Advanced SoftwareTechnology (EAST) which,within a tirnescale of six years,aims to develop factories thatcan produce computer pro-grams and other software morereliably than is currently poss-ible. The United Kingdomcompany CAP Industries Ltd istaking part in the project.There are also two approvedendeavours in the field of laserwelding. both of which willutilize the expertise of Britain'sWelding Institute. Aimed atdeveloping existing carbonmonoxide and dioxide lasers,these two projects could re-place conventional arc weldingand machine cutting tech-niques within ten years.In addition, three British univer-sity departments and sixcompanies are to work on thedevelopment of electron -beamwelding for steel up to 100 mmthick, together with firms fromSpain and Sweden. And theRoyal College of Surgeons iscontributing to the design ofOperating Room 2000 whichwill find its place in theautomated hospital of five yearshence as an integratedworkplace for surgery and in-tensive care.

Agreed standardsIn almost all cases, participantsfrom different countries willhave to agree on technical start-

EE

October 1987

dards before the first designscan be drawn up. Ministers inStockholm set up committees toexamine specifications for thehigh definition television. andPrometheus projects as an in-itial step in this direction. In the

long run, Eureka's success willbe measured in the world'smarkets and. to be marketableits products must set new com-mon standards in Europe andthe rest of the world.A British proposal accepted at

the Stockholm conference willhelp pave the way around suchobstacles. The idea is to exam-ine the training that should begiven to managers to cope withinternational research projects.As a pilot stage, the United

Kingdom has undertaken tofund a detailed survey of 1000participants in 20 Eureka pro-jects to identify the issuesneeding to be tackled. (LPS)

PRODUCTS NEW PRODUCTS NEIA1

New low cost,high stabilityresistorsA new family of metal filmresistors offering the perform-ance of wirewound resistors at afraction of the cost is nowavailable from Verospeed. Fea-turing very low tolerance com-bined with a high degree ofthermal stability, they are idealfor applications where pre-cision components need tooperate reliably even underadverse conditions.Known as EBG Type EE1/8,these silicone coated metal filmresistors have a temperaturecoefficient of only 15 ppm overthe temperature range between+25 and +85 °C, and a closetolerance of 0.1%. This specifi-cation applies right throughthe range from 10 ohms toI megohm. With full militaryand DIN approval, these com-ponents are ideal for appli-cations requiring high stabilityunder heavy load and in ex-treme environmental con-ditions. Maximum workingvoltage is 250 V, and power dis-sipation is 0.25 W at 70 °C drop-ping to 0.125 W at 125 °C.Housed in a black epoxy resinmoulding, overall body size is10 x 3.2 mm. Values are givenin an easy to read numeric for-mat. For example, a 1 kilohm re-

sistor with a 0.1% tolerance islabelled 1001.Verospeed can supply thesecomponents ex -stock, withsameday despatch.VerospeedStansted RoadBoyatt Wood Industrial EstateEastleighHants S05 4ZY.Telephone: (0703) 641111Telex: 477144 BV DIST G

(3654:4)

IntroducingSuper OctopusThe latest version of the Oc-topus universal work holdersystem incorporates a numberof design and manufacturingadditions that enhance its con-venience and range of appli-cations. Available from Free -trade (TEP), the Super Octopusnow incorporates a large 21/2inch diameter high quality lensthat allows fine work to be car-

ried out and with reduced eyestrain.Freetrade has also changedthe material of the flexibleworkholding arms to a blackanodised pure aluminium formore positive positioning of ob-jects and the grip clips are nowin a matching all -metal blackfinish.Both the Super Octopus and thepopular Octopus models con-sist of a base block secured to awork surface using a clampmechanism and have four five -inch long flexible 'Stayput'wires. The Super Octopus Kit isfitted with two work clamps, thelens and a magnetic workholder. The arms can be angledprecisely to give infinitelyvariable positioning of the workfor accurate work such assoldering and glueing.The Super Octopus is availablecomplete with handy wallet at arecommended retail price of£7.95, excluding VAT.

Freetrade (TEP) LimitedMoor LaneWittonBirmingham B6 7HH.Telephone: (021 356) 2582

(3654:16:F)

-a- 41, 0

i

I ' , -0

, i 1

. ,.,.,

00

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4c.1

EE

October 198764

OT PRODUCTS NEW PRODUCTS NENew multi-purpose testerModel TP55N is the latestanalogue multimeter to be an-nounced by TMK Instrumentsand is a general purpose instru-ment offering many features at areal value for money price. Thepivot and jewel mechanismanalogue meter is overload pro-tected, has a large clear 31/2inch scale with a mirrored90 degree arc and knife edgepointer to minimise parallax er-ror. Safety has been built in tothis rugged and reliable toolthat complies with UL 1244 andVDE 0411 requirements and ithas both fuse and diode inputprotection.An easy to operate single rotaryswitch complemented by po-larity reversal caters for thetwenty measuring ranges whichinclude: Six dc voltage rangesfrom 100 mV to 1000 V with asensitivity of 20,000 ohms/voltand 3% accuracy - Four ACvoltage ranges to 1000 V with8,000 ohms/volt sensitivity and

an accuracy of 4% - Four directcurrent ranges go from 50 pA to10 A - Resistance from 0 to20 Mohms in four ranges with a20 ohm centre scale - &is arefrom -10 to + 62 dBs. Appli-cations are further increased forthis versatile TMK multimeterby the addition of a new styleTransistor Test function thatcaters for both PNP and NPNtypes and indicates both Typeand Quality via a simple pushbutton. Model TP55N comesready for use, measures 120 x150 x 45 mm, weighs just370 gms and is fully guaran-teed. The TP55N costs £24.75exclusive of VAT.

Harris Electronics (London)Limited138 Grays Inn RoadLondon WC1X 8AX.Telephone: (01 837) 7937Telex: 892301 HARTRO G

(3654:12:F)

Super EPROMsimulator forPCsThe Octagon EPROM SimulatorSystem, now available fromEngineering Solutions Limited,Maidenhead, provides a low-cost and reliable means ofsimulating up to four 32 KbyteEPROMs simultaneously.Up to four simulator pods canbe connected to the same PCcard, and my be loaded in se-quential, parallel or interleavedmodes. Interleaved mode trans-fers consecutive bytes into con-secutive pods, thus allowingtwo pods to represent a 16 -bitword, or four pods to representa 32 -bit word.The system features a powerfuldebug and diagnostic facility:the unique "Debug Window"allows the program running inthe target system to com-municate back to the PC via itsEPROM socket. The DebugWindow works by allowing theprogram to peform read oper-ations on a group of designatedmemory loqations in a speciallydefined sequence. This causesbytes of data to be transferredthrough to the PC and dis-

played sequentially.When pod loading is com-pleted, a Restart Probe auto-matically restarts the targetmicroprocessor which fetchesinstructions and data from theSimulator Pod. The system'sControl Software can be con-figured to hold the microcom-puter's restart -line high or low,as required.The Octagon EPROM SimulatorSystem consists of MSDOS-com-patible Loader and Debug Win-dow Programs, PC card, aone -metre ribbon cable andone Simulator Pod containing32 Kbytes of RAM. Pods can bespecified with 250 or 200 nS ac-cess times. Header cables,Multi -Pod Adapter Cables andRestart Probes are also avail-able to complement the system.Engineering Solutions Limitedspecialises in providing low-cost hardware and softwaretools for the professionalengineer.Engineering Solutions LimitedKing's House18 King StreetMaidenheadBerkshire SL6 lEF.Telephone: (0628) 36052Telex: 849462 TELFAC GFax: 0628 74928

(3654:19:F)

65 EE

October 1987

PRODUCTS o NEW PRODUCTS NO

Best features ofhard -disk andfloppy storagecombined innew systemEconomical, easily -expandablemass storage is provided by thenew TakeTen system from DataTechnology Corporation, nowavailable from the Euro Elec-tronics division of LivingstonTechnical Sales.Currently produced for IBMPCs and compatibles, TakeTenis a 51/4in half -height disk drivewhich uses a 10 Mbyte flexiblemedia cartridge. The systemprovides infinitely expandabledata storage which is transport-able and secure, and offers anopportune means of implemen-ting the requirements of theData Protection Act. TakeTen isavailable in single- and dual -drive versions, for space -savinginternal fixing or as a neat,unobtrusive standalone mod-ule.The disk drive combines the

best features of hard disk andfloppy technologies. TakeTenemploys a voice coil motor foraverage access time of 65milliseconds (equalling the per-formance of an average fixeddisk drive), proven embedded-

servo tracking technology,'crashless' high -capacity con-tact read/write heads, self -centring hub, and a hard pro-tective shell. LSI Technology isextensively used to ensure highreliability. The drive isequipped with a built-in in-telligent SCSI controller sup-porting a subset of theCommon Command Set, auto-matic error detection and cor-rection, automatic defect map-ping, fault -tolerant recoveryand self -diagnostics.One-off prices for add -in andadd-on units are £750 and £825respectively for single -driveversions, £1350 and £1385 fordual -drive versions, with a one-off media price of £45 dis-counted to £25 for hundred -upquantities.

Livingston Technical SalesLimitedLivingston House

2-6 Queens RoadTeddingtonMiddlesex TWIT OLR.Telephone: (01 977) 0055Telex: 23848Fax: 01-977 6431 (3456:22:F)

New VSWR andpower meterThe new DC1500A VSWR/power meter from Coline fea-tures instantaneous analogueindication of "forward" powerallowing easy "peaking" oftransmitter output and in ad-dition incorporates continu-ously variable gain/sensitivityof indication to allow adequatedeflection of meter at allpower/frequency combi-nations.Compact and reliable, thisdirect -reading British made in-strument is completely self-contained and easily portable,giving clear digital readout.The DC1500A offers a simpleand effective solution to theproblem of measuring powerand return loss of fixed andmobile installations over a widefrequency range (30 MHz to1.5 GHz). It is an active devicewhich can be used across itsfull bandwidth without the ad-dition of plug-in units or otheraccessories. When measuringpower, the DC1500A operateson a 'first principle' techniqueenabling power to be measuredindependently of frequency,allowing the instrument to becalibrated at DC.Enclosed in a tough case (op-tional carrying case available),the DCI500A embodies a num-

ber of useful features-simpledirect reading of power andVSWR, true RMS power read-ing, wide bandwidth, low cur-rent drain, low battery powerindication.It has many applications in bothmilitary and civilian fields -army,navy, airforce, cellular radio,police, motoring organisations,fire and ambulance services,car hire companies, municipalauthorities, marine and airportservices and private organis-ations.Powered by a PP3-type battery,the DC1500A has high accuracy.When measuring power (DC to1.5 GHz), it is accurate within5% with a fast response time(less than 15 seconds to 98% offinal reading). When measuringVSWR (50 ohm impedance, fre-quency 30 MHz to 1.5 GHz), theaccuracy is typically within -2to +8% of indicated reading,depending upon the powerlevel.The DC1500A is available withor without accessories. TheMobile Radio Kit, is designedfor convenience, comprisingthe DC1500A meter completewith 50 watt dummy load, twoconnecting cables, a set ofcable adaptors, rugged carry-ing case and instructionmanual.

Coline Limited166 Great North Road,Hatfield,Hertfordshire, AL9 5JN.Telephone: 07072 60423Telex: 22543FAX: 07072 75547 (3654:21:F)

EE

October 198766

13W PRODUCTS NEW PRODUCTS NEA

Miniature PCBjack socketsWatts International announces arange of PCB -mounting minia-ture jack sockets with a differ-ence.

Unlike traditional jack socketsthese Japanese -manufacturedunits feature an all -enclosedhousing. All pin contacts, andmake/break contacts, arehoused within the small plasticpackage. Two and three -poleversions are available withsingle and multiple make/break switching options. Mech-anical fixing strength is en-hanced using locating spigots.Watts InternationalComponents LimitedSuite 6Wyvern House46-48 High StreetBOGNOR REGIS P021 1SPTelephone: (0243) 868322

(3630-15F)

68000 trainingsystemThe Flight Electronics 68000training system can now beused either in stand-alone con-figuration, using a terminal asthe control console, or in con-junction with a mini or main-frame as a target board.The training system (FLT -68k)helps engineers to learn pro-gramming and develop appli-

cations using the Motorola16/32 -bit 68000 microprocessor.The built-in line assembler anddebugging facilities enable it tobe used stand-alone, using anyterminal, PC, or microcomputerwith a serial port as the controlconsole.Flight Electronics LtdAscupart StreetSOUTHAMPTON SOl 1LUTelephone: (0703) 227721

(3630-17F)

IBM computerkeyboardThe IBM Industrial ComputerKeyboard is now available fromPPM Instrumentation Ltd. It is afully feature keyboard de-signed to attach directly to theIBM 7531 Industrial Computer,for use in the harsh environ-ment of the factory floor.Like the computer for which itis designed, the keyboard ishardy enough to stand up to the

tough industrial atmosphere,and carries an FCC class Arating. To prevent unauthorisedusage, there is a locking systemon the computer which protectsthe diskette area and deacti-vates the keyboard.PPM Instrumentation Ltd7 Riverside Business CentreWalnut Tree CloseGUILDFORD GUI 4UGTelephone: (0483) 301333

(3630-12F)

New source ofhighperformancestrobe tubesA competitively -priced rangeof popular replacement tubesfor stroboscopes is announcedby Electronic and ComputerWorkshop Ltd. (ECW).ECW can supply, on short ordertimes, tubes suitable for a rangeof applications, from high -power photographic 'flash'systems to timing lights, discoeffects and scientific instru-ments. Wire and socket ter-minated versions are includedand all are supplied with asuitable choke and installationinstructions.The following types are of-

fered:100 Ws output 400 V operation

58538 4 Ws output 315 V operation

S4668 45 Ws output 400 V operation

STC-150 150 Ws output with plug-in octal

base and built-in choke

All types are available by mailorder to ECW at £7.32 for theS106A, £8.40 for the S8538, £8.57for the S4665 and £20.36 for thehigh performance STC-150. Allprices include VAT and post/packaging.Electronic & ComputerWorkshop Limited171 Broomfield RoadChelmsfordEssex CM1 1RY.Telephone: (0245) 262149.

(3654:3)

67 EE

October 1987

ON PRODUCTS NEW PRODUCTS NEIA1

New highperformancebipolar logicarraysannounced byAMCCApplied Micro Circuits Corpor-ation (AMCC) have introducedfive logic arrays comprising itsnew Q5000 Series. These arraysoffer the highest speeds anddensities of any AMCC bipolarproducts. 05000 Series circuitdesigns will be competitve inspeed and density with arrayswhich consume much greaterpower. Q5000 Series arrays haveapplications in hi-rel commer-cial and military systems wherehigh performance is required."The new Q5000 Series arrayscombine the proven tech-nology of AMCC's oxide -iso-lated Q3500 products withincreased performance anddensity derived from de-creased geometries," statedAMCC's Director of EuropeanSales and Marketing, Ian Scott."By introducing these new ar-rays. I am convinced we will ex-pand our opportunities forapplication fits in many marketsegments, including fiber op-tics and electronic warfare".As with all other AMCC bipolarproducts, the arrays featuremixed ECL/TTL mode inputs/outputs (I/Os), speed/powerprogrammable macro logic andfull military screening. Typicalgate delays of between 210 and545 picoseconds (ps), based onthe complexity and availabilityof speed/power macro options,are archievable. The Q5000products and their equivalentgate densities are: the 01300T(1300 gates); the QM1600T (1600gates with 1280 bits of on -chipRAM); the Q2400T (2400 gates);the Q3500T (3500 gates); and theQ5000T (5000 gates).All products in the Q500 Serieshave been designed to providea systems approach to high per-formance semicustom appli-cations.AMCC's MacroMatrix designkit, an integrated cell library in-cluding a wide variety of MSImacros and software tools, is

available for designs on Daisy,Mentor Graphics, Tektronix/CAE and Valid workstations, aswell as Tegas V on VAX/VMS.The highly efficient Q3500Tachieves maximum ECL inputfrequencies of 600 MHz. Maxi-mum input frequencies of160 MHz can be expected in theTTL mode. The Q3500T hastypical power dissipation of be-tween 2.5 and 6.0 Watts. Actualpower dissipation will dependon the mix of macros, speed/power options and percentageof array utilization.Typical cell utilization is 95%using automatic placement androuting. The Q500 productshave between 76 and 160 usableprogrammable I/O cells per-mitting interface to TTL. ECL10K, ECL 100K or 5 -volt refer-enced ECL.The Q5000 Series is available ina number of ceramic packagesincluding leaded and leadlesschip carriers, dual -in -lines, pingrid arrays and surface mountswith lead counts as large as 196pins. Typical design cycle fromnetlist capture to prototyperanges from 10 to 14 weeks.AMCC specializes in the de-sign and manufacture of high-speed, high -reliability semi -custom integrated logic circuitsfor commercial and military ap-plications. Its bipolar, CMOSand new BICMOS logic arraysserve the high performance re-quirements of the instrumen-tation and automated testequipment, computer, elec-tronic warfare, graphics andtelecommunications markets.Applied MicrocircuitsCorporationSlington HouseRankine RoadBasingstokeHampshire RG24 OPH.Telephone: (0256) 468186Telex: 859898 BUREAU GFax: (0256) 460 168 (3654:2)

LED clockdisplaysThe majority of displays in therange of LED clock and multi -digit displays available from

Selectronic are now available ina new bright red colour. Thedisplays, which are manufac-tured by Taiwan Liton, are alsoavailable in green and standardred versions. The new brightred colour offers a claimed 50%increased light output over thestandard red, at an increasedcost of between 5 and 10%.Display height varies from 0.2in(5 mm) to 1.8in (45.7 mm). Thelarger displays in the series (0.7;0.9; 1.4; 1.5; 1.8in and themagnified array) are availableonly in bright red.The displays offer betweenthree and 12 digits, with threedrive options available: directdrive, duplex or multiplex.Selectronic LimitedThe Old Stables46 Market SquareWITNEY OX8 6ALTelephone: (0993) 73888

(3630-14F)

Highperformance61/2 -digit DMMNew from PPM Instrumentationis the Prema 6000, a high resol-ution digital multimeter withIEEE 488 interface costing just£975.Offering an input resistance of1Gohrn up to ±2 V, and with100 nV resolution, the 6000 hasan excellent price/perform-ance ratio. True RMS values aredetermined for alternatingvoltage, alternating current, andtemperature measurementswith PRTs conforming toIEC 751. Four mathematics pro-gramms allow the display of off-set corrected values, per centdeviation, dB, and dBm.PPM Instrumentation Limited7 Riverside Business CentreWalnut Tree CloseGUILDFORD GUI 4UGTelephone: (0483) 301333

(3630-30F)

EE

October 198768

PRODUCTS NEW PRODUCTS NEVNew highqualityloudspeakersIn line with their policy of con-tinuing research and develop-ment, Morel have announcedthe forthcoming introduction ofa new range of high quality,high sensitivity drivers, the firstof which is the MDT 33 SoftDome Tweeter.It is an extremely fast Tweeterusing a 28 mm (1.1") diametervoice coil and a chemicallytreated soft dome, and is ideallysuited for two-way systems withthe possibility of a lower thannormal crossover frequency, aswell as for three and multipleway systems.Incorporating the Morel Hexa-tech voice coil technique, alu-minium wire wound on analuminium former and usingflexible wire termination en-sures excellent high frequencyperformance with exceedinglyhigh power availability. Thepower handling is further en-hanced by using Ferrofluid inthe magnetic circuit.The magnetic system itself is aningenious Morel double mag-net design and is completelyshielded regards stray flux andextraneous magnetic field. It

produces a high magnetic fieldin the gap of 25,000 gauss and aforce factor (BXL) of 6.1 WB/M.By venting into the enlargedarea of the double magnetsystem, a low resonant fre-quency of 650 Hz is obtainedwith a remarkable smooth rolloff from 1000 Hz through thisdamped resonance area. Thesubsequent wide range re-sponse of 1800-20000 ± 0.6 dB(1000-40000 - 5 dB) is obtainedwith a harmonic distortion ofbelow 0.8% for 3rd harmonicover this entire range. Thisholds for 2nd harmonic distor-tion from 3 kHz upwards with aslight increase in distortion inthe 1 to 3 kHz. This with a sensi-tivity of 94 dB for 1 watt and1 metre, and a power handlingcapability of from 250 to1000 watt subject to crossoverfrequency.With such a dome tweeterdesign, the acoustic qualities atlower than normal crossover

frequencies are excellent withan absense of honking, andeven at the more normal cross-over frequencies this excellentacoustical behaviour is evidentto the ear. With the low cross-over frequency available andhigh power capability, it is idealfor consideration in two waysystems using a 10" or 12"

woofer.To utilise the dome at the lowerthan normal crossover fre-quency available, it is necess-ary to have a sharp roll offbelow 1000 Hz to keep thedome operating in the low dis-tortion area. This makes it idealfor use with active systems. Themounting plate is anodisedbrushed aluminium plate of110 mm diameter and 3 mmthickness.This superb tweeter is sold inpairs, each pair having beentested and matched to within± 0.5 dB in sensitivity, andpresented in an eye-catching in-formative presentation box.They will be packed four pairsper outer, and orders should bein multiples of this quantity.Price: £42 per pair.Also new from Morel is thePP8.2 8 inch push-pull woofer,an improved version of the PP8.There is now a double magnetin each motor, increasing theflux from 0.52 T to 0.74 T for5 ohm version, and 0.78 T for8 ohm version. The height of thegap is now 6 mm as opposed to5 mm. The sensitivity is there-fore increased to 91 dB 1W/1Mfor single voice coil operationand 94 dB 1W/1M for both coilsin parallel or series connec-tions. There is no -change in theappearance of the unit. Theprice is £27.20 each (withgrille).Another interesting new loud-speaker is the MW 1252 12"Woofer with a diaphragmmanufactured from highlydamped black polymer olefincomposite. This uses a 52 mmdiameter voice coil manufac-tured by the Morel Hexatechtechnique, incorporating alu-minium wire on an aluminiumformer.The substantial magnetic cir-cuit provides a force factor of8.92 WB/M, resulting in a fasthigh power handling unit. Theconventional magnetic circuit is

located within the very shallowdepth (95 mm) of the mag-nesium pressure cast chassis.The olefin diaphragm with itspolyurethane surround anddust cap has been carefully de-signed to give excellent rigiditydespite its shallow depth. Witha resonant frequency of 22 Hz,we have a driver of exceptionalsmooth response from 18 Hz to2500 Hz, with a particularly ex-cellent off -axis response at 45degrees up to 1500 Hz beforesmoothly rolling off.The acoustic performance isone of good controlled bass,with an openness and a qualityof detail throughout its fre-quency spectrum. It can, nat-urally, be considered as anexcellent driver for three orfour way systems, but moreunusual, in conjunction with theMDT 33 Dome Tweeter, pro-duces a two way system of ex-cellent performance and capa-bilities. The price is £29 each(packed in pairs). Detailed tech-nical information on theseloudspeakers is available fromMorel (U.K.) Limited11 Foxtail RoadNacton Road(Ransomes)Industrial EstateIpswich IP3 9RT.Telephone: (0437) 719212Telex: 987601 Morel G (3654:1)

CombinedCMOS Memoryand ClockCardThe Vector InternationalMMD16-CMOS RAM memorycard distributed by ElectronSystems (Sandy) combines 4 or16 Kbytes of non-volatile RAMmemory with power failuredetection logic, a Date/Timeclock and an interrupt gener-ating watchdog circuit.Most JEDEC bytewide 2 or 8 KCMOS RAM chips can be in-stalled in the card's twomemory sockets which haveheaders to allow compatibilitybetween different chip types.Power failure detection logic

monitors and power input andinitiates a non-maskable inter-rupt in the event of a powerfailure. Data stored in thememory is protected for up to25 days by an on -board nickelcadmium rechargeable batterypack after power is removed.The Date/Time clock maintainstime of day (hours, minutes,seconds) and date (year, month,day or month, day of week) andcan generate alarm interruptsfor second, minute or hourly in-tervals. While time-out inter-rupts for specific applicationscan be generated by the card'swatchdog circuit. This containsa monostable which whenenabled can trigger standardMMD16 but interrupts.A charging circuit and a "bat-tery low" status indicationfeature are also included on thecard.Electron Systems (Sandy)LimitedTelephone: (0767) 81195 (3654:5)

New batteryholdersBulgin have introduced twonew battery holders as shown.

The one at the top is a 1/2AA sizetype for PCB or base mounting,and the other is a 4 x AA (R6)type for panel mounting.A.F. Bulgin & Co PLCBypass RoadBARKING IG11 OAZTelephone: 01-594 5588

(3630-22F)

EE

October 1987

BAKERS DOZEN PARCELSFr,:e per carce 3(1 CO t,_.1 yn, 12

get one eine bee.As the parcels listed below re 5.o -rd new compOnentS.Ur -loss marked 5.h.

1 - 5 13 amp ring r-.4 - - - - - roseS2 -5 13 arnp ririe _ ..._ o.oses5 - 3 Push

- 4 in Bei , , .o-th nears8 - 2 130 nen - , eerrients

10 -2 nos . 12v 34a secondaries11 - I e.s. _ flet fat 614" Speaker12 -5 con 3 ii., fa to , or valves13 - 12 gSas roar -I sr -:r14 - 4 OCP photo transistors16 - 4 tape heads. 2 recood. 2 erase

- I ulna sonic transmitter and 1 ditto receiver13 - 2 15033 mfd corripsda grade efectrobscs19 -2 15711 dependent reasion20 - 5 dfferea Snitches21 - 2 main' interference StrINIteSS01522 - 2 25 wan crossover units 2 way23 - 1 40 watt 3 way croSsaaa tone23 - 1 6 6911 counter Mains voltage33 - 2 Niaed battery chargers31 - 1 key snitch with key32 - 2 horridly snitches33 - 2 aerosol cans of ICI Dry Lubricant34 - 96 1 metre lengths colour coded connectin:

woes35 - 2 74 spaced 2 gang tuning cordensors37 2 said daeleetric 2 gang tuning conderson38 - 10 compression trineress41 - 6 Rocka Snitches 10 amp Maas SPST43 - 5 Rocker Switches 10 amp SPOT Centre OH44 - 4 Rocker SwitChes 10 amp OPOT45 - 1 24 hest fine snitch f133315 Operated (s_h I46 - 6

49 - 10 r-4:- -7o.c4rsghthghts53 - 2 0o.24VAC4COrolays51 - 1 . 2C 0 very SenSilive relay52 - 1 12. 4C relay53 - 2 roars operated relays 3 8 amp changeovers55 - 1 locking rnechalwrn AIM 2 keys56 M-nalute UniSelectOr is-ribciocutt foe electric igian57 - 5 DaSs* Hearse switches60 - 5 ferrite rods 4" 5,16 diameter aerials61 - 4 ferrite 543t with L67.1 wave cods - 4 200 ohm _ io _oes63 - 1 ?.!o -3--t . :tot trigger module64- 10 : - - spindles65 - 5 f mostals, mainly bemetal66 - Magnets: brake - stops rotation irstantly67 - Low meware 3 level switch

70 - 2 75 .. - - ' -.CO ohm71 - 4 _ 18. 33. 50 and 10) ohm

77 - 1 terse re,- .- . 1-60 mans78- 5-5 amp slot 403s

mains fa" stack - ts steel,86- 25' ai fan blades Es 1i," shaft87 - 23" aast , La,!,.3 !! "." shaft

93 4 11 pin P.' - for relayS94 - 5 B7G va.o o55 -4 skated . .e bases96 - 1 therm: toe 2, loidge98 - 1 odsz snitch (sh

101 - 1 2 - os detay snitr_h103 - I , - , moner supply urst104 ' . ...onto supper soil105 1 end panel socket

109- 10i. " . :

112 - 1 ft-.

------------118 - Teak Etter: -.: : 5 Speaker C4t:120 - p.c.b. Mu: 2 _- o and 17 _t- o- recs.122 - 10 miss ram !lex white pot -sister132 - 2 plastic Doors i " - nions ideal for interrupted

beam switch etc155 - 3 vanicap push button tuners vdth knobs188 - 1 plastic boa, sloping metal front. sdel6 95rnen.

average depth 45rren241 - 1 car door speaker (very RA 614" 15 ohm made for

Radomobile243 2 speakers 6' 4" 15 den 5 wan made for

Radian -wade265 -2 mans mast orders 9V SA secondary spirt canary

so OK also for 115V267 - I maim ttansformer I5V IA secondary PCB

mountingaao - 2 6v -36v mains transformer .3A p c b mounting350 - AO doable pole leaf snitches360 - 1 7uf 663. 501st metal cased condenser4532 - irs 80olan lardspeakers4542 - 21. in. Bolan Loudspeakers463 1 - ma'am operated relay with 2 Sets £10 contacts4542 - packets tiSin risen,- sealer- with cures465 3 54 tOund 3 pai plugs nal fit don 193

4 7 segment led. do3p10.3.547.,o4 - pc boards for striPong. 101S of valuable parts473 1 -5140wn Wake, with bat in rAveter R32,3

mob.]487.1 - 3A double pole rnagrete yea saves repairing

fuses4964 - 150Ouf 25v and electrotync -apisaron

TELEPHONE BITS.taster SOCket lhas surge arrester - ringng condenser etcl andtiles 13.7 plugCaine:ran socket -------------£2.96Dual adaptors 12 from one socket) 055Coed terminating with B.T. plug 3 metres . (1.00Kit for converting old entry marina/ boa to nen 9.t rrestersocket, complete with 4 core cable, cableotos and 2 BT...tension sockets C11.50100 min 4 core telephone cable (8 50

COMPACT FLOPPY DISC DRIVE EME-101ire 02E-101 on, a 03 cf.: of the rare m3-4 afich despise,s snag sore orvodes a caoaca of 5.-Ck per dsc. nisch oeroinaent to me 5's' Caso

setchi the Opetatoss 1.ta.g and other /Monroe:ion dice -rot',C.., Ia5r5r 355353513 33735,..013352 sac. Soensuon.Arrested arc. Al at viit wire of C27S0 nolairn 34.53O3 VAT. Data anabtie separatay 12. refund:tie d so, pacreseme drrve,_

EVERLASTING BATTERIES! 51,e5 riot can. but if sou don't zetacan. the Whom batten- has in anon a seed ufe. mum maids

sale for ernagency. stands" 6 applca fert.alto fat Quasii-S-nks and esmimento that dm. a?! .1-.03C00.4 osarpet, TheChien eatery we haw es .3s 4.4 steue as bg a -id uses as 20 conPr= 2 fa CI tel 812048. Note dwa cog 31.0 03 031,35C: oar refED -M.

3 POLE MODEL MOTOR ova operate from as tin as 1.5.- and spelayes aesease straloy as toe vatax is coo -nod. a: .9v 1,VOVV.C.,omonor makes over and the wad unsays ea-aro.' - as deal rnr_ceeFor a ...Ada_ Sae amain 20rm 40arn easii tam -sett and wth 9007saga garde_ 60p each our tel 831430

CASSETTE STEREO TAPE HEADS with ina,-,troa breacts and Matape sucks pars. one nosed itilituck and 'etEl D541.

OPTRO INTERRUPTER consists of a IR - tee close tosghr t resistor Men Itglid or IR a trot chasnynt ofreS=a-r_e cal be made to se-SM or operate a - usefoiaor-ang r-otto- stopeag at Price 2 for 0 rc l545.

VERNER TIME SWITCHMans coastal V*15h 20 anew snitch. ate anand ore off par 24 Pas tavern deTYarto-naticaly oarearg for to lo-gdienrgat not stionenag day. An enevone ranwitch but so., can have Is foe Orgy 12.95wohout case. metal case - 12_95. adaptorle to commt this into a fennel 20a rareswath but MO she added a:has:age of as to12 °wolfs ter 247es This makes an deal

CoElesinarY Roa,d- calucaa for ti -e arnertion (meta. Pr= ofGuaranteed 12 months_ w..x,e, i.t e

12 volt MOTORS BY SMITHSIs. use Cr- cos. etc. Vase see vent

sue -sell and task, reverotak Soc 3'r -cc Tda. Trey Ice.,, a coed length of

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This Month Snip9" VDU OR MONITOR deal to A01 not or-outa or winocanna teas Poi= Lisa and node tube rcf1,35C STOW33.0,1 VIII X RE, tali -non prOteasto _ 3-_-1ni.--er and Ian a 311.0 bases end 1111 many It-, 16.do soar to set it gong ITS 05.40 tap is a tact, - . -

nok tut 1305 *pas salts so should be casedmth a doe wid fie toe cold Ina e a case out 0 2 or our 614"Smoke caterers! T1.0 VDU 0511533 CC,5-55,:5 43373nsard has teen Erne tested and 1 -as a. ---------tee Of*vat at a tot len some fano 2 - - : -De dorc,are 116 piss f3 peels We - Inatat alas brent ncet but Off3Sed at 01 than 13vast We do a kit fa de 16. 23 pea to r_ _ : nos ,norcfcrPrice is 0 our rot 3.026

SUDE SWITCHES Sub mnahroe see on, - 4 non sagecoin otarge coin re11 Pree 5 tot El 'F.- 5:653.

LOW VOLTAGE RELAY 031.00.14 3.5v cal. pug n dl sockets 53 c oconmns 5121.4 nen of lewd at a say case 2 kr El ref 813635

POLARISED RELAY dope--4-no upon as drottion, do corral as bre74 kla males the omen C372.3. so I card be used to protect deiced.e25M.3,5s553 at 05 cn carts insuato. 01,35.53 53113.23 5r55 SIC 2 fa ri

ref 80500

SLOTTED OPTO SWITCH rifia rid antler ad salsa snorted vsslotted neuting so dos de earner bean Mien Ii0,1-311 33.33.1.3 05.1raostas sneer.. can be used n nationo vadat spars sensing atroc Wee 2 for ref 30515

206 TIME SWITCH BoyainfutOr made malt West German preen°,Joss ure3ft 4 sauce Aim Mama c o contacts cart Le se anwesnearound 247v dal to the nearest 15 inns aro antri a over -ride swat.Pet BPS tad nary we hew oNy 330.

COMPUTERS the Act." -Beaten- as used n rwly iwsools tocones and salad jobs. Wass ego color or Booth acid WhiteT_V Procer once was £135. ate Price rser.---I act working C45 0 par revel out siglay tawny 128- post aid laYb* 103430but cot noning 00 - cost_ al are new 4333 comp;etewith mars PS U.. 323 page 1,--hdhcat. TV had, aril startercassette. Fort range of Softwee also n stock at wry Ion

TELEPHONE LEAD 3 mss bang torraveng we end welt oats BT.fat plug and the otner erd arts 4 =road( eadoved coded 55335 to fdto rItXe- or .hppiance_ Replaces the bed on ad or -taco maimedeavnia fly am ET smite P.te El ted E0552 a 3 oaref 79101.

POWERFUL IONISER.Gaeraes accrov 10 tmas now IONS den de ETI Orr -farcasters Wo roes/. low home. oda._ shoo, 35553i..3075 etcStoles you fog tetra and was hada - a Cornp3..3o:cc,,-t cc-4,3 E950 I2P6P

J Et N BULL ELECTRICALDEPT. EL, 250 PORTLAND ROAD

HOVE, BRIGHTON,SUSSEX BN3 5QT

MAIL ORDER TERMS, CASH. P.O. a aiet.e nom 000. Ckanrstrvls CZ add Cl server s-ts,s9., Vtara,ks 3=0.11 015535 DOC....=00,,,Itrans .1..orio and putie tompanes Its,. gLeeess b onto,accered Phow Edgmon 2773. 730543 a 2075:0

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£2 POUNDERS31,121 1 contircd coos -non mach ad corn -post hr baer coma

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DIGITALTHERMOMETER

Dual Scale ThermometerA neat digital thermometer with internal andexternal sensors displaying C or F. Theexternal sensor is a waterproof probe (max.length 3m). Temperature range -5'C to50°C (internal), -20°C to 70°C (external).Includes a 12 hour clock.Order Code FD25C Price £9.95

Pocket ThermometerA well made temperature meter displayingC and a 12 hour clock. Temperature

range -5'C to 50°C (internal), -20-C to70 C using external probe (max. length900mm). High and low temperatures can beset and an alarm sounds when these arereached. A set lock switch preventsaccidental resetting.Order Code FD26D Price £14.95

Temperature ModuleVersatile thermometer module displays in =C orincludes a 12 hour clock and serial data output.Temperature range -5'C to 50°C (internal),-20°C to 70°C with external probe. Overall size68 x 35 x 23mm deep. Probe (max. length 3m) andbezel also available.Module Order Code FE33L Price £6.95Probe Order Code FE34M Price £2.50Bezel Order Code FE35Q Price 15pAll prices include VAT. Please add 50p towards postage.Prices firm until 6th November 1987. Subject to availability.Harder below £5.00, please add 50p handling.

ELECTRONIC SUPPLIES LTD.

Mall Order: P.O. Box 3. Rayleigh, Essex SS6 8LR. Tel: Southend (0702) Sales: 554161.Enquiries: 552911; Trade sales: 554171, Trade enquiries: 552961.

ShopsBirmingham: Sutton New Road, Erdingtort, Birmingham. Telephone: 021 384 8411London: 159-161 King Street. Hammersmith W6. Telephone: 01 7480926.Manchester: 8 Oxford Road. Telephone: 061 236 0281.Southampton: 46-48 Bevois Valley Road. Telephone: 0703 225831.Southend-on-Sea: 282-284 London Road. Westcliff-on-Sea, Essex. Tel: 0702 554000.All shops except Manchester and Birmingham closed all day Monday.

Pick up a copy of our 1987catalogue from any branch ofW.H. Smith for just £1.50.Or to receive your copy bypost just send £1 .50 40pp & p to Mail Order address.If you live outside theU.K. please send £2.50 or 11International Reply Coupons.