4 0 3

An Improved Method of MCXO

Absbr~icb--'h improve the MCXO pcuformn~icc nnd sirn- plify its structnre, si now MCXO dosign mnt,hod has h e i i d C V O l G p C d . Though deleting pulses of cluck signal of n microcomputer and sliifting its phase, thc hquenoy- tcmpcrntnre stdi1iLy of MCXO can he m u r k satisfactory, atid the DDS chip, which i H orkn used iri high perfornianco MCXO, cnn bo climiriatod.

Sovcral diffcrent MCXOs I i w c b c m mnde with this incthod nnrl diff@rorit perfornimicc spccificntiuris can be oh- tniriccl. Rcr:tidirig to t h e Ainiplicity, in H wide tompertitiirc rnngn frririi -40 to +80°C, thc fi.cqll~ncy-tornparntrire stn- Idity of thc MCXOn can be from 4 3 x l U - * tn A2 x l op7 .

&.- I

IVig. 1. A simple MCXO ldock diagn1.i~.

4116

.................................................................................................

r : . .

*50-40-30-20-10 0 IO 20 30 4050 6 0 7 0 80

30 -

1'EMP,DEG C

17g. :1. 'I'ypicnl j - 7' (:iirw ~ v i t h prcwwing clock cyclc and phase.

Smic cxporimcnts have hcen done to compare and check t l ~ rh;irar:toristics of tlic MCXO. Fig. 2 and 3 show the same MCXO tcrripcriihrc icst, nwilts.

Comparing Lhc two Incnsiii~fitiiciit rwults oric (:ill1 firid that with proccssirig tlic clock cyclc mid phase of the microcomputer , higbcr resolution, E~ecluency-tcniperat,nrc stability, nnd frequency stability of the oritput signal

ain be obtuird. Many otlior methods to cnhaiicc thc phase control rcsolution a.rc? being rescnrcliixl, and het tcr MCXO performance cu.11 hc! nbtained. Spccifications for t)ett,er perforrnnrice includc! frcquency, I O MHq frcquency- temperuturc! skability, 2ct3 x frorn -40 l o +8OoC; short-t.erm ~ t . d ) i l i ~ ~ > , 1 x IO-’//s; power corimmpLiori, 5 v DC nncl 75 rnW; and agiiig: 1 x IW’/cI.

I3ecause tlic piilse dclr?t,inn and phnsc shift nra done pcii- odically a.nd continuously, spi~rious hequeiicir!s in h e out- put do not exist. In the MCXO, dditionnl circuits required Cor the ~ U ~ S C dcletion xad dolay circuitry iirc fiimplc digitti1 cim1it.s itrid iriiich simplcr thun Ihe DDS.

This papcr gives a, simple MCXD rlcsign approach. For cliff(:lr!rit; application piuyoses, Inany other rricl;hods ca.n IN: cnmbiricrl. F‘or exa.inplc:, pari circuits c m l ~ c in a “slecp” stjiLt;[> lo dccrcaw the inpul po.urcr.

V. CONCLUSION

h(:cording to the twt results obtniiied iri CHIT MCXO, thc UUS chip can hc oinilted and r c p l i l d by circuitry that processes microcomputer clock pi~lscw ancl phasc. As ;I rcsull, h e st,ructurt! of MCXO cnn h r ! simplified. When this method is uscd t,n design cornmcrcial MCX.Os (fm Exam- ple, tempcrittiirc! rnrige from 0 t,o W C ) , hei r frrqiwncy- teinpcriitura st;hility can 1~ hotter! and thc cosi is much lower I

. , j

,. : i I ’ ~

” . :

Wei Zhou wnr l m ~ n in 9unc 1916. [-le gradu- ntcd h r n Lhc Elcctronic Engincwiug I)up,tct- incril of Xi’ari Jiao Tong Uriirwsil,y i i i 1970. Roin 1.970 t r i 1988, l in worlccd at Shaanxi 111-

I stitiitr for Mcasurcmcnt mid T&iue tm c u i

. . . . . ,

Zongqinng Xunn w m born in 1980 ~ I I Siixmxi provinco, Chiiia., Now hc is a seriior cnginccr in t.lic Depsrtrricut, nC Measureuietit ~ L I I ~ Instrument, Xitiinn University, CliiiiiL. Ifis r,iirronL rmetirdt iritorwtc; iiicludc dccLronic instrument drwigril tilricGcquency s i g r d ~>r’nccss- ing, aticl micrucorri piitar conipcnsated crystal oscillator dcsign.