part 8-elec buk(final)
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PART 8 TRANSISTORS and AMPLIFIERS
I. TRANSISTOR FUNDAMENTALS
TRANSISTOR Developed in December 23,1947 in Bell laboratories
By John Bardeen, William Shockley and Walter Brattain
Basically a resistor that ampliies electrical imp!lses as they are transerred
rom its inp!t to its o!tp!t terminals"
Basic Types
1. BIPOLAR JUNCTION TRANSISTOR (BJT) #t is a three layer semicond!ctor device consistin$ o either t%o & and one '(
type layers o materials or t%o ' and one &(type layers o semicond!ctor materials"
T!ee !e"i#ns #$ BJTa" Base
)e$ion to %hich carriers lo% rom emitter to collector
1*17 dopants+cm3
oderately doped
b" -mitter )e$ion rom %hich carriers lo%
1*
19
dopants+cm
3
.eavily doped
c" /ollector )e$ion to %hich carriers lo%
1*10 dopants+cm3
i$htly doped
ar$est
BJT S%!&c%&!e and C#ns%!&c%i#n
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/0 Transistors and Amplifiers
T!ansis%#! C&!!en%s and C#n$i"&!a%i#ns a" /ommon Base /oni$!ration
#n this circ!it, the inp!t si$nal is applied at the emitter, the o!tp!t is taken at the
collector and the base is the common terminal his has very lo% inp!t impedance
Apa ( ) #n the dc mode the levels o #/ and #- d!e to maority carriers are related by a !antity
called alpha and deined by the ollo%in$ e!ation5
e
c
I
I
b" /ommon -mitter /oni$!ration he inp!t is applied at the base, the ampliied o!tp!t is taken rom the
collector, and the emitter is the common terminal" his circ!it is the one $enerally !sed or transistors beca!se the /- ampliier
has the best combination o c!rrent and volta$e $ains
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Transistors and Amplifiers - 2
Ie c3 II
Be%a (β) )atio o the collector c!rrent to the base c!rrent
β =3
c
I
I
c" /ommon /ollector /oni$!ration his circ!it has the inp!t applied at the base, the o!tp!t taken at the emitter
terminal and the collector is the common terminal #mpedance matchin$
4a55a (δ
) 6or%ard c!rrent $ain or common collector coni$!ration
δ
3
e
I
I
C#5pa!is#n #$ A5pi$ie! C#n$i"&!a%i#ns
Ca!ac%e!is%ic C#55#n
Base
C#55#n
E5i%%e!
C#55#n
C#ec%#! P#e! 4ain moderate hi$hest moderate6#%a"e 4ain hi$hest moderate less than 1C&!!en% 4ain lo%est less
than1moderate hi$hest
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/7 Transistors and Amplifiers
Inp&%I5pedance
lo%est moderate hi$hest
O&%p&%I5pedance
hi$hest moderate lo%est
PaseIn'e!si#n
none 1*8 !t o phase none
Appica%i#ns )6 amp !niversal isolation
T!ansis%#! Biasin" Bias
an electrical, mechanical, or ma$netic orce applied to a device to establish a
desired electrical or mechanical reerence level or its operation" is a D/ volta$e or c!rrent that sets the operatin$ point or ampliyin$ the :/
si$nal
a" 6i;ed Bias is taken rom a battery or po%er s!pply
b" Sel Bias he ampliier prod!ces its o%n D/ volta$e rom an #) drop across a resistor in
the ret!rn circ!it o the common terminal" Sel(bias is probably the type o bias !sed most oten beca!se it is economical
and has stabili<in$ eect on the D/ level o the o!tp!t c!rrent" /an be emitter stabili<ed or collector stabili<ed
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Transistors and Amplifiers - 8
c" =olta$e(Divider Bias he most stable type o circ!it biasin$
d" Si$nal Bias
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/9 Transistors and Amplifiers
Re"i#ns #$ T!ansis%#! Ac%i#n
a" :ctive )e$ion Base(emitter !nction is or%ard biased and the collector(base !nction is
reverse biased" ransistor>s active operation as an ampliier
b" Sat!ration )e$ion both !nctions are or%ard biased
s%itch on operation or the transistor
c" /!t o )e$ion
both !nctions are reverse biased s%itch o operation or the transistor
L#adine and :/p#in%
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Transistors and Amplifiers - ;
L#adine is a strai$ht line dra%n on the collector c!rves bet%een the c!t(o
and sat!ration points o the transistor :/p#in% ?@!iescent 'ointA is the operatin$ point o the transistor %ith the time
varyin$ so!rces o!t o the circ!it
Re'ie :&es%i#n< iven the circ!it belo%, dra% the D/ loadline
:nalysis5 :t c!t(o, #c C * th!s =/- C =//
:t sat!ration, =/- C * th!s #c C =// + )c
BJT S5a Si"na Anaysis
=/Pa!a5e%e!s<
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/ Transistors and Amplifiers
1" hi ( short circ!it inp!t impedance
Ii
6ii
=
(6# >)
2" hr ( open circ!it reverse volta$e $ain ?volta$e eedback ratioA
! 6#
6i (Ii >)
3" h ( short circ!it or%ard c!rrent $ain
$ Ii
I# ( 6# >)
4" ho ( open circ!it o!tp!t admittance
# 6#
I# (Ii >)
0. FIELD EFFECT TRANSISTOR (FET) Unipolar device beca!se they operate only %ith one type o char$e carrier
Voltage controlled device %here the volta$e bet%een t%o o the terminals
?$ate and so!rceA controls the c!rrent thro!$h the device" aor eat!re is very high input resistance
a. J&nc%i#n Fied E$$ec% T!ansis%#! (JFET) perates %ith a reverse(biased '& !nction to control c!rrent in the channel
S!are la% device beca!se o the relation o #D and =S
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Transistors and Amplifiers - ?
ID C
0
)#$$ (4S
4SDSS6
61I
J6-+D(S6- transer characteristics /an be n(channel or p(channel
JFET Sy53#s
Ope!a%i#n #$ JFET J6- is al%ays operated %ith the $ate(so!rce '& !nction reversed biased
)everse biasin$ o the $ate(so!rce !nction %ith ne$ative volta$e prod!ces a
depletion re$ion alon$ the '& !nction %hich e;tends into the n(channel andth!s increases its resistance by restrictin$ the channel %idth as sho%n in theprecedin$ i$!re"
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/1> Transistors and Amplifiers
DC Biasin" $#! JFET 1" 6i;ed Bias
a separate po%er so!rce"
2" Sel Bias
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Transistors and Amplifiers - 11
3" So!rce Bias
4" =olta$e Divider
3. Me%a O@ide Se5ic#nd&c%#! Fied E$$ec% T!ansis%#! (MOSFET)
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/10 Transistors and Amplifiers
second cate$ory o the ield eect transistor
beca!se o the presence o an ins!lated $ate then it is sometimes called
#6-s S6-S diers rom J6- in that it has no '& !nction str!ct!re
#t has t%o basic types, D ES6- and - E S6-
Depe%i#n MOSFET (D/MOSFET) he drain and so!rce are di!sed into the s!bstrate material and connected by
a narro% channel adacent to the ins!lated $ate #t can be operated in t%o modes(the depletion mode or the enhancement mode
and sometimes called depletion+enhancement mode S6- #t can be operated %ith a <ero, positive or ne$ative $ate(so!rce volta$e
&ormally operated in the depletion mode
When coni$!red as s%itch, it is normally(on
Depe%i#n M#de &e$ative $ate to so!rce volta$e is applied
n Echannel is depleted o some electrons hence decreasin$ channel
cond!ctivity
Enance5en% M#de positive $ate volta$e is applied
more cond!ction electrons are attracted to the channel th!s enhancin$ channel
cond!ctivity
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Transistors and Amplifiers - 12
Enance5en% MOSFET (E/MOSFET)
operates only in the enhancement mode has no depletion mode
it has no str!ct!ral channel
it has no #DSS parameter
or an n(channel type o this device, a positive $ate volta$e above threshold
ind!ces a channel by creatin$ a layer o ne$ative char$es ?inversion layerA inthe s!bstrate portion that is adacent to the Si2 layer"
:n n(channel -(S6- has a positive =S %hile a p(channel -(S6- has
a ne$ative =S
he cond!ctivity o its channel is enhanced by increasin$ the $ate to so!rce
volta$e 6or $ate volta$e belo% the threshold, there is no channel to be ormed
# coni$!red as a s%itch, this device is normally o
LD MOSEFT, VMOSFET and TMOSFET are -S6- technolo$iesdeveloped or hi$her po%er dissipation
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/17 Transistors and Amplifiers
II. AMPLIFIERS
-lectronic devices capable o ampliication or increasin$ the amplit!de o
po%er, c!rrent or volta$e at its o!tp!t /irc!its desi$ned to increase the amplit!de or level o an electronic si$nal"
Fsed as boosters
Cassi$ica%i#ns #$ A5pi$ie!s< 1. Acc#!din" %# F&nc%i#n
a"=olta$e :mpliier =olta$e controlled so!rce
p(amps are volta$e ampliier
b"/!rrent :mpliier /!rrent controlled so!rce
BJs are c!rrent ampliier
c"'o%er :mpliier Boost the po%er level o the si$nal
0. Acc#!din" %# C#n$i"&!a%i#n a" /ommon Base :mpliier
ransistor ampliier %here inp!t is applied at the emitter and o!tp!t is taken
rom the collector terminal he base is common to both inp!t and o!tp!t
a;im!m c!rrent $ain is 1
&o phase inversion rom inp!t to o!tp!t
b" /ommon /ollector :mpliier ?emitter ollo%erA ransistor ampliier %here inp!t is applied at the base, o!tp!t is taken rom the
emitter terminal a;im!m volta$e $ain is 1
/apacitors m!st have a ne$li$ible reactance at the re!ency o operation
&o phase inversion rom inp!t to o!tp!t
c" /ommon -mitter :mpliier
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Transistors and Amplifiers - 18
ransistor ampliier %herein the inp!t is applied at the base and the o!tp!t is
taken rom the collector terminal here is a phase inversion rom inp!t to o!tp!t
2. Acc#!din" %# Cass #$ Ope!a%i#n a" /lass : :mpliier b" /lass B :mpliier c" /lass / :mpliier d" /lass :B :mpliier
Cass A Cass B Cass C Cass AB
E$$iciency 0*G 7"0G 1**G Bet%een :H B
C#nd&c%i#nAn"e
3I*° 1*° Belo%
1*°
Sli$htly$reater
than 1*°
Dis%#!%i#n o% .i$h e;treme moderate
Bias(3ase e5i%%e!)
inear portion
:bovec!t(o
Belo%c!t(o
c!t(o
inp!t o!tp!t
o!tp!t o!tp!to!tp!to!tp!t
C#5pa!is#n #$ A5pi$ie! Casses
7. Acc#!din" %# F!e&ency a" D/ :mpliier
:mpliies D/ si$nal?<ero re!encyA
b" :!dio :mpliier :mpliies si$nal %hose re!ency is %ithin the a!dio ran$e?2* .<(2*.<A
c" )6 :mpliier :mpliies si$nal %hose re!ency is %ithin the radio re!ency ran$e
d" #6 :mpliier
:mpliies si$nal %hose re!ency is in bet%een the carrier and the mod!latin$re!ency e" =ideo :mpliier
: %ide(band ampliier that ampliies video si$nal
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/19 Transistors and Amplifiers
=ideo si$nal reers to the re!ency ran$e o the pict!re inormation %hich
arises rom the television scannin$ process
8. Acc#!din" %# %e Si"na 3ein" a5pi$ied a" Small Si$nal :mpliiers
:mpliier that !tili<es only the very linear portion o the active device
b" ar$e Si$nal :mpliiers :mpliier that !tili<es almost the !ll rated o!tp!t po%er o the active device
9. Acc#!din" %# Me%#d #$ C#&pin" a" Direct /o!plin$
:mpliiers connected or co!pled %itho!t any passive component in bet%een"
b" /apacitive /o!plin$ :mpliiers are connected or co!pled by the !sed o capacitor termed as
co!plin$(capacitor
c" #nd!ctive /o!plin$ :mpliiers are connected or co!pled by the !se o ind!ctor or transormer
d" ransormer /o!plin$ ost oten, ind!ctor is not !sed as co!plin$ device instead transormer is !sed
;. P#e! A5pi$ie!s a" '!sh('!ll :mpliiers
:mpliier %ith t%o similar circ!its operatin$ in phase opposition"
ne ampliies hal o the cycle and the remainin$ hal is bein$ ampliied by the
other ampliier
b" /omplementary ESymmetry :mpliiers '!sh(p!ll ampliiers !sin$ complementary transistors s!ch as pair o pnp and
npn
c" @!asi(/omplementary :mpliier '!sh(p!ll ampliiers !sin$ the same transistors at the o!tp!t b!t the driver is
!sin$ complementary transistors
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Transistors and Amplifiers - 1;
C#5p#&nd C#n$i"&!a%i#ns a" /ascade /onnection
a cascade connection is a series connection %ith the o!tp!t o one sta$e then
applied as inp!t to the second sta$e" he cascade connection provides a m!ltiplication o the $ain o each sta$e or
a lar$er overall $ain"A' A'1A'0A'2.. A'n
A'(dB) 0>#" (A')
b" /ascode /onnection a cascode connection has one transistor on top o ?in series %ithA another
his arran$ement is desi$n to provide hi$h inp!t impedance %ith lo% volta$e
$ain to ens!re that the inp!t iller capacitance is minim!m"
c" Darlin$ton /onnection he main eat!re o the Darlin$ton connection is that the composite transistor
acts a sin$le !nit %ith a c!rrent $ain that is the prod!ct o the c!rrent $ains o the individ!al transistors"
#t is a circ!it meant to boost inp!t resistance
D 1 0
d" 6eedback 'air he eedback pair connection is a t%o(transistor circ!it that operates like the
Darlin$ton circ!it #t !ses a pnp transistor drivin$ an npn"
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/1 Transistors and Amplifiers
TEST OURSELF 8 Re'ie :&es%i#ns 1" : '&' transistor is made o
a" siliconb" $ermani!mc" carbond" either silicon or $ermani!m
Anse! d" either silicon or $ermani!m
2" he transistor is !s!ally encaps!lated ina" $raphite po%der b" enamel paintc" epo;y raisind" black plastic
Anse! c" epo;y raisin
3" 'o%er transistors are invariably provided %itha" solder connectionsb" heat sinkc" metallic casin$d" scre% bolt
Anse! b" heat sink
4" he transistor speciication n!mber 2& reers to aa" diodeb" !nction transistor c" 6- %ith one $ated" S/)
Anse! b" !nction transistor
0" Which i the ollo%in$ is necessary or a transistor actionKa" the base re$ion m!st be very %ideb" the base re$ion m!st be very narro%c"the base re$ion m!st be made rom ins!latin$ materials
d" the collector re$ion m!st be heavily doped
Anse! b" the base re$ion m!st be very narro%
I" :s compared to a /B ampliier a /- ampliier has
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Transistors and Amplifiers - 1?
a" lo% c!rrent ampliication
b" hi$her c!rrent ampliicationc"lo%er inp!t resistanced" hi$her inp!t resistance
Anse! b" hi$her c!rrent ampliication
7" #t is the most stable type o circ!it biasin$a" sel(biasb" si$nal biasc" volta$e(divider biasd" i;ed bias
Anse! c" volta$e(divider bias
" he !iescent state o a transistor implies
a" <ero biasb" no o!tp!tc" no distortiond" no inp!t si$nal
Anse! d" no inp!t si$nal
9" -ach o the 2 cascaded sta$es has a volta$e $ain o 3*" What is the overall $ainKa"3b" 9c" 3*d" 9**
Anse! d" 9**S#&%i#n
total C ?3*A?3*A C 9**
1*" Which class o ampliiers operates %ith the least distortionKa"/lass :b" /lass Bc" /lass /d" /lass D
Anse! a" /lass :
11" Which o the ollo%in$ circ!it is the astest s%itchin$ deviceKa" J6-b" BJc" S6-d" riode
Anse! c" S6-
12" Which o the ollo%in$ device is a !nipolarKa" 6-
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/0> Transistors and Amplifiers
b" BJc" Lener diode
d" -D
Anse! a" 6-
13" he cascaded ampliier %hich is oten !sed in the #/ isa" ind!ctively co!pledb" capacitively co!pledc" direct co!pledd" transormer co!pled
Anse! c" direct co!pled
14" .i$hest operatin$ re!ency can be e;pected in case o a" bipolar transistor b" J6-c" S6-d" #6-
Anse! a" bipolar transistor
10" Which o the ollo%in$ is e;pected to have the hi$hest inp!t impedanceKa" S6-b" J6- ampliier c" /- bipolar transistor d" // bipolar transistor
Anse! a" S6-
1I" he MMMMMMis !ite pop!lar in di$ital circ!its especially in /S %hich re!ire very lo% po%ercons!mption"a" J6-b" BJc" D(type S6-d" -(type S6-
Anse! d" -(type S6-
17" What is the ampliication actor in 6- transistor ampliiersKa" Lib" $mc" #Dd" #
Anse! b" $m
1" he -(S6- is !ite pop!lar in %hat type o applications"a" di$ital circ!itryb" hi$h re!ency
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Transistors and Amplifiers - 01
c"b!erin$
d" a, b and c
Anse! d" a, b and c
19" : J6- !st operates %ith speciicallya" the drain connected to $ro!ndb" $ate to so!rce '& !nction or%ard biasedc" $ate connected to the so!rced" $ate to so!rce '& !nction reverse biased
Anse! d" $ate to so!rce '& !nction reverse biased
2*" he main dierence o a S6- rom a J6- is that
a" J6- has '& !nctionb" o the po%er ratin$c" S6-S has t%o $atesd" S6-s do not have physical channel
Anse! a" J6- has '& !nction
21" : small si$nal ampliier a" !ses only a small portion o its loadlineb" al%ays has an o!tp!t si$nal in the m= ran$ec" $oes into sat!ration once on each inp!t cycled" is al%ays a common emitter ampliier
Anse! a" !ses only a small portion o its loadline
22" he parameter he corresponds toa" ND/
b" N :/
c" r>ed" r>c
Anse! b" N :/
23" # the D/ emitter c!rrent in a certain transistor ampliier is 3 m:, the appro;imate val!e o r>e isa" 3Ob" 3Oc" "33 Od" *"33 O
Anse! c" "33 O
S#&%i#n
r>e C Ω= II"7m:3
m=2I
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/00 Transistors and Amplifiers
24" he inp!t resistance o a common base ampliier isa" very lo%
b" very hi$hc" the same as /-d" the same as //
Anse! a" very lo%
20" -ach sta$e o a o!r sta$e ampliier has a volta$e $ain o 10" he overall volta$e $ain isa" I*b"10c" 0*I20d" 3*7
Anse! c" 0*I20S#&%i#n
=over(all C ?10A?10A?10A?10A C 0* I20
2I" he ma;im!m eiciency o a transormer co!pled /lass : ampliier isMM"a" 20b" 0*c" 7"0d" 1**
Anse! b" 0*
27" #n a S6-, the process o creatin$ a channel by the addition o char$e carrier is called"a" ind!cementb" improvementc" balancin$d" enhancement
Anse! d" enhancement
2" What is the c!rrent $ain o a common base circ!it calledKa" $ammab" deltac" bravod" alpha
Anse! d" alpha
29" he name o the very irst transistor a" diodeb" !nction transistor c" point contact transistor
d" triode
Anse! c" point contact transistor
3*" )e$ion in a transistor that is heavily doped"
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Transistors and Amplifiers - 02
a" collector
b" emitter c" based" $ate
Anse! b" emitter
31" #n a common Ebase ampliier the volta$e $ain isMMMMM"?:pril, 2**3Aa" medi!mb" lo%c" <erod" hi$h
Anse! d" hi$h
32" #n a common collector ampliier, the inp!t resistance isMMM"?&ov,2**3Aa" hi$hb" <eroc" medi!md" lo%
Anse! a" hi$h
33" : depletion S6- ?D(S6-A can operate %ith %hich o the ollo%in$ $ate(so!rcevolta$eK ?&ovember, 2**3A1" <ero2" positive3" ne$ative
a" 1 onlyb" 2 only
c" 3 onlyd" 1, 2 and 3
Anse! b" 3 only
34" What problem is ca!sed by a loosely co!pled transormer in an )6 ampliierK ?:pril, 2**4Aa" a too narro% bandpassb" over co!plin$c" optim!m co!plin$d" a too(%ide bandpass
Anse! a" a too narro% bandpass
30" &ormally, ho% are hi$h po%er t!bes testedK ?:pril, 2**4Aa" vis!allyb" individ!allyc" in their circ!itd" !se portable testers
Anse! c" in their circ!it
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/07 Transistors and Amplifiers
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