Automatic Gain Control (AGC) circuits Theory and design by Isaac Martinez G.

Transcription

1 EE35 Analog ntgratd rcuts ntroducton Automatc Gan ontrol (AG crcuts Thory and dsgn by saac Martnz G. n th arly yars of rado crcuts, fadng (dfnd as slow varatons n th ampltud of th rcvd sgnals rqurd contnung adjustmnts n th rcvr s gan n ordr to mantan a rlatv constant output sgnal. Such stuaton ld to th dsgn of crcuts, whch prmary dal functon was to mantan a constant sgnal lvl at th output, rgardlss of th sgnal s varatons at th nput of th systm. rgnally, thos crcuts wr dscrbd as automatc volum control crcuts, a fw yars latr thy wr gnralzd undr th nam of Automatc Gan ontrol (AG crcuts [,]. Wth th hug dvlopmnt of communcaton systms durng th scond half of th XX cntury, th nd for slctvty and good control of th output sgnal s lvl bcam a fundamntal ssu n th dsgn of any communcaton systm. Nowadays, AG crcuts can b found n any dvc or systm whr wd ampltud varatons n th output sgnal could lad to a lost of nformaton or to an unaccptabl prformanc of th systm. Th man objctv of ths papr s to provd th hypothtcal radr wth a dp nsght of th thory and dsgn of AG crcuts rangng from audo to F applcatons. W wll bgn studyng th control thory nvolvd bhnd th smpl and prmary da of an AG systm. Aftr that, wth th thory as our gud, w wll study and dscrb th charactrstcs and prformanc of th most popular AG systm componnts. Fnally, a fw practcal AG crcuts wll b prsntd and analyzd. At ach scton, mphass wll b mad on thos parts of th crcut that could b potntally mplmntd n an ntgratd crcut form. A lst of rfrncs wll b prsntd at th nd of ths papr for th vntual radr who could b ntrstd n larnng or radng mor about ths subjct. Unvrsty of Toronto Fall 00

2 EE35 Analog ntgratd rcuts Thory of th Automatc Gan ontrol systm [,,9] Many attmpts hav bn mad to fully dscrb an AG systm n trms of control systm thory, from psudo lnar approxmatons to multvarabl systms. Each modl has ts advantags and dsadvantags, frst ordr modls ar asy to analyz and undrstand but somtms th fnal rsults show a hgh dgr of naccuracy whn thy ar compard wth practcal rsults. n th othr hand, non-lnar and multvarabl systms show a rlatv hgh dgr of accuracy but th thory and physcal mplmntaton of th systm can bcom rally tdous. From a practcal pont of vw, th most gnral dscrpton of an AG systm s prsntd n fgur. Th nput sgnal s amplfd by a varabl gan amplfr (GA, whos gan s controlld by an xtrnal sgnal. Th output from th GA can b furthr amplfd by a scond stag to gnrat and adquat lvl of. Som th output sgnal s paramtrs, such as ampltud, carrr frquncy, ndx of modulaton or frquncy, ar snsd by th dtctor; any undsrd componnt s fltrd out and th rmanng sgnal s compard wth a rfrnc sgnal. Th rsult of th comparson s usd to gnrat th control voltag ( and adjust th gan of th GA. AG block dagram [] Fgur Snc an AG s ssntally a ngatv fdback systm, th systm can b dscrbd n trms of ts transfr functon. Th dalzd transfr functon for an AG systm s llustratd n fgur. For low nput sgnals th AG s dsabld and th output s a lnar functon of th nput, whn th output rachs a thrshold valu ( th AG bcoms opratv and mantans a constant output lvl untl t rachs a scond thrshold valu (. At ths pont, th AG bcoms nopratv agan; ths s usually don n ordr to prvnt stablty problms at hgh lvls of gan. Unvrsty of Toronto Fall 00

3 EE35 Analog ntgratd rcuts Many of th paramtrs of th AG loop dpnd on th typ of modulaton usd nsd th systm. f any knd of ampltud modulaton (AM s prsnt, th AG should not rspond to any chang n ampltud modulaton or dstorton wll occur. Thus th bandwdth of th AG must b lmtd to a valu lowr than th lowst modulatng frquncy. For systms whr frquncy or puls modulaton s usd, th systm rqurmnts ar not that strngnt. AG s dal transfr functon [] Fgur As mntond bfor, an AG systm s consdrd a nonlnar systms and t s vry hard to fnd solutons for th nonlnar quaton that ars durng th analyss. Nvrthlss, thr ar two modls that dscrb th systm s bhavour wth a good dgr of accuracy and ar rlatvly asy to mplmnt whn th small sgnal transfr quatons of th man blocks ar known (whch s usually th cas. Dcbl-basd AG systm [] Fgur 3 Unvrsty of Toronto Fall 00

4 EE35 Analog ntgratd rcuts Although thr s no nam for th frst modl, t could b dscrbd as th dcbl-basd lnar modl. Th block dagram for ths modl s show n fgur 3, n ths modl th varabl gan amplfr (GA P has th followng transfr functon. P K + a K Whr and ar th output and nput sgnal, K s a constant and a s a constant factor of th GA. Followng th sgnal path w fnd that th logarthmc amplfr gan s: + a ln ln K Whr K rprsnts th gan of th nvlop dtctor. Assumng that th output of th nvlop dtctor s always postv (othrws th logarthmc functon bcoms complx whch translats n a non workng crcut, th output of th logarthmc amplfr s a ral numbr an th control voltag bcoms: F(s( F(s( ln K F(s rprsnts th fltr transfr functon. Knowng that th GA shows an xponntal transfr functon w can apply th logarthm functon at both sds of th quaton. ln a + ln K Thus, th control voltag can b xprssd as: a ln ln K Usng th xprsson for that w found bfor ln [+ af(s] ln + af(s + ln K af(s ln K Snc w ar only ntrstd n th output-nput rlatonshp, lt K and K b qual to on. Thus, th abov quaton bcoms: ln [+ af(s] ln + af(s f and ar xprssd n dcbls, w can us th followng quvalnc Thn, ln ln.3log.3 0 db 0.5 db db Unvrsty of Toronto Fall 00

5 EE35 Analog ntgratd rcuts Fnally, th quaton that rlats nput and output (both n db can b rwrttn as db 8.7aF(s db + + af(s + af(s Ths typ of AG systm shows a lnar rlatonshp as long as nput and output quantts ar xprssd n dcbls. From th last xprsson t s asy to s that th bhavour of th systm s dtrmnd by th a factor of th GA and th fltr F(s. F(s s usually a low pass fltr, snc th bandwdth of th loop must b lmtd to avod stablty problms and to nsur that th AG dos not rspond to any ampltud modulaton that could b prsnt n th nput sgnal. An mportant paramtr n any control systm s th stady-stat rror that s dfnd as [5] : ss lm (t lm se(s t whr E(s s th rror sgnal n th fdback path. Applyng th dfnton gvn abov to th AG systm w fnd that th poston rror constant s gvn by: ss + af(0 whr F(0 s th D gan of th F(s block and a s th constant factor of th xponntal law arabl Gan Amplfr (GA. Thus, n ordr to mantan th stady stat rror as small as possbl th D gan of th F(s block (usually a low pass fltr must b as larg as possbl. Th smplst F(s block that can b usd n th systm s a frst ordr low pass fltr whos transfr functon s dfnd as follows: K F ( s s + B whr K s th D gan of th fltr and B s th bandwdth. Usng ths xprsson n th quaton of th stady stat rror w fnd that: ss + ak And th total D output of th AG systm s gvn by: D 8.7aK D + + ak + ak s 0 Unvrsty of Toronto Fall 00

6 EE35 Analog ntgratd rcuts t can b sn that f th gan loop K s much gratr than, th output s almost qual to 8.7 and th stady stat chang n th nput s gratly rducd. AG systms that nclud a rfrnc voltag nsd th control loop ar rfrrd as dlayd AG. Th scond modl of an AG systm dos not contan a logarthmc amplfr wthn th loop but stll contans a xponntal typ GA. Dspt th fact that th systm s complxty ncrass, t s stll possbl to fnd small sgnal modls for small changs from a partcular opratng pont []. Th block dagram shown n fgur 4a can rprsnt such systm. t s mportant to notc that th GA and th dtctor ar th only nonlnar parts of th systm. Assumng unty gan for th dtctor and th dffrnc amplfr, th systm can b rducd to th block dagram shown n fgur 4b. Psudolnar AG systm [] Fgur 4 Hr, o and ar nput and output sgnal rspctvly, F s th combnd transfr functon of th fltr and dffrnc amplfr. Th output voltag o qual P, whr P rprsnts th gan of th GA and t s a functon of th control voltag c. Followng th sgnal path, w can s that th control voltag s gvn by: ( F Unvrsty of Toronto Fall 00 r Snc w ar ntrstd n th chang n th output voltag du to a chang n th nput voltag w can tak th drvatv of o wth rspct to, thrfor: d d d d (P P + dp d

7 EE35 Analog ntgratd rcuts Th last drvatv on th rght sd of th quaton can b furthr dvlopd applyng th chan rul and usng th quaton for th control voltag, thus: dp d dp d d d dp d d d do Thrfor, th xprsson for an b rwrttn as: d d d dp d d ( F d Altrnatvly d d + F dp d P d / dp F d / + d t s clar that th loop gan s a functon of th nput sgnal, whch translats nto a rlatv dgr of non-lnarty and complcats th analyss of th transnt rspons of th systm, snc th pol locaton s also dpndant on th nput sgnal. Nvrthlss, t s possbl to numrcally valuat th charactrstc paramtrs of th loop f th P( functon s know and a st of ntal condtons s takn as an startng pont. All th AG systms consdrd hr provd a contnuous samplng of th output sgnal and a contnuous adjustmnt of th GA. Thr ar a fw applcatons whr th output sgnal s sampld at spcfc ntrvals of tm and gan s adjustd only at thos ntrvals. Thos systms ar known as puls-typ AG systms and ts analyss s usually prformd usng sampld data tchnqus. - omponnts of an AG systm Thr ar many componnt and crcut confguratons that can b usd as a varabl gan amplfr (GA, whch s th man componnt of an AG systm. Th man factors that must b takn n consdraton whl slctng a sutabl crcut ar: frquncy rspons, avalabl control voltag, dsrd control rang of th GA, and sttlng tm and fnally, systm confguraton. Unvrsty of Toronto Fall 00

8 EE35 Analog ntgratd rcuts Th followng crcuts can b usd form th low to th rado frquncy rang assumng that thy ar mplmntd usng th propr tchnology and consdrng mportant practcal ssus such as bypassng, ground plans, mpdanc matchng, parastcs, and componnt slcton. a Low frquncy crcuts For low frquncy crcuts th most common confguraton conssts of an opratonal amplfr and a voltag controlld attnuator. Th basc voltag controlld attnuator conssts of a fxd rsstor connctd n srs wth a fld ffct transstor (usually a JFET workng n th trod rgon. Such confguraton s shown n fgur 5. Basc voltag controlld attnuator [3] Fgur 5 t can b shown that th output voltag s gvn by: out n L + (+ g L ds (+ g As gs approachs gs(off, g ds approachs to zro an thr s no attnuaton of th nput sgnal. f th valu of L s much hghr that r ds(on and th abov quaton smplfs to: out Th output transconductanc s gvn by: Whr: g ds g dso n + g GS(FF ds ds GS(FF L GS L g dso DSS GS(FF ombnng both quatons: Unvrsty of Toronto Fall 00

9 EE35 Analog ntgratd rcuts out + g dso n [( / ] GS(FF GS GS(FF Th abov crcut has two srous drawbacks, hgh harmonc dstorton and lmtd sgnal handlng capablty. Both problms can b solvd by fdng back on half of dran- sourc voltag to th gat, such modfcaton smplfs th output transconductanc quaton to: g g ds dso GS(FF whch s a lnar functon of c. To avod loadng th output th valu of th fdback rsstors must b hghr than, and f solaton from th control voltag to th output s dsrd a followr must b connctr btwn th fdback ntwork and th output. aoltag controllr attnuator wth fdback bwth fdback and solaton [3] clnarzaton du to fdback ntwork Fgur 6 Th followng crcuts llustrat th us of a voltag-controlld attnuator nsd th fdback loop of an opratonal amplfr. For th frst crcut (Fgur 7, th ovrall gan of th stag s gvn by: A + g dso - GS(FF X Unvrsty of Toronto Fall 00

10 EE35 Analog ntgratd rcuts arabl gan opratonal amplfr [3] Fgur 7 f a mnmum gan gratr than s rqurd (Fgur 8, a scond rsstor can b plac n paralll wth th JFET. Ths arrangmnt ntroducs an xtra factor of / n th abov quaton, thus: A + + g dso - GS(FF arabl gan opratonal amplfr wth A mn > [3] Fgur 8 Fnally, n ordr to block any D componnt that could b prsnt n th nput sgnal and kp th FET workng n dp trod rgon, a capactor must b placd n srs wth th FET attnuator. Th valu of th capactor wll dpnd on th rqurd cut off frquncy and th quvalnt mpdanc sn from th conncton pont. S fgur 9. X Unvrsty of Toronto Fall 00

11 EE35 Analog ntgratd rcuts oltag controllr attnuator [3] wth D blockng capactor Fgur 9 Whn usng FET as a componnt of a voltag attnuators t s mportant to kp n mnd th followng ssus: a Th FET n trod rgon bhavs as a rsstor only for small voltag valus of DS. b Th output transconductanc (g ds s approxmatly a lnar functon of GS. c Th lnarty of g ds dcrass as GS approachs GS(FF. d Fdng back on half of DS to th gat of th FET mprovs lnarty and dynamc rang. Fnally, f a dffrntal control voltag s avalabl th FET attnuator can b mplmntd as follows. FET attnuator wth dffrntal c [3] Fgur 0 Th control voltag of ths crcut only nds to b on half of that of th convntonal attnuator to achv th sam valu of g ds, but th mprovmnt n lnarty an dynamc rang ar prsrvd. X Unvrsty of Toronto Fall 00

12 EE35 Analog ntgratd rcuts b Hgh frquncy crcuts Most of th abov crcuts can b usd of to a fw hundrds of mgahrtz, dpndng on th componnt slcton, groundng, bypassng, mpdanc matchng and physcal layout of th crcut. Nowadays, wth th hgh prformanc rqurmnts of modrn systms and dvcs t s advsabl to study th most common tchnqus that ar typcally mplmntd n ntgratd crcut ( form. Th frst dvc that can b found n ntgratd and dscrt form s th Dual Gat MSFET or DG-MSFET. Ths dvc can b modld as two MSFET n cascod confguraton wth th nput sgnal appld to th frst gat (G, and a scond control sgnal appld to th scond gat (G. Ths scond sgnal controls th gan of th ovrall stag and t s usually rfrrd as th AG sgnal. Fgur [6,7] Th usful frquncy rang and lctrcal charactrstcs of th DGMSFET s hghly dpndant on th tchnology usd durng th fabrcaton of th dvc. Untl now th bst dvcs hav bn fabrcatd usng HEMT (Hgh Elctron Moblty Transstor tchnology for ggahrtz rang and convntonal MS tchnology for lowr frquncy applcatons. Although DGMSFET shows good hgh frquncy prformanc, t s not wdly usd du to th lack of accurat modls and a poor undrstandng of ts charactrstcs. Nvrthlss, a larg amount of rsarch has bn alrady don and now t s possbl to fnd som SPE modls for commrcal dvcs (Slconx and Phlps morovr, an xprmntal modl for ggahrtz applcatons was dvlopd and optmzd by. Lcqursh, M. J. Hows and. M. Snowdn at th Unvrsty of Lds usng S paramtrs [7]. X Unvrsty of Toronto Fall 00

13 EE35 Analog ntgratd rcuts DGMSFET quvalnt modl [7] Fgur Th scond topology that s commonly found n hgh frquncy crcut s th Glbrt cll or analog multplr [8,9,4]. Although t was prmarly dsgnd to b usd as a mxr, t has bn ncludd as a fundamntal part of varabl gan amplfrs such as th LXXX srs of Natonal Smconductor []. A complt dagram of a four quadrant multplr crcut s shown n fgur 3. Th collctor Four quadrant analog multplr [9] Fgur 3 X Unvrsty of Toronto Fall 00

14 EE35 Analog ntgratd rcuts currnts of T and T4 can b shown to b: Also, applyng KL v + ( + h v ( + h b b E5 E7 + + v ( + h v + ( + h Usng th xponntal rlatonshp for th mttr currnt of T5 and T6 and dvdng ombnng th last two quatons: E5 E5 E6 + Applyng KL at th collctor loop of T3 and T4 Thus, E5 can b rwrttn as: BE5 E5 BE6 + E6 E8 (BE5 BE6 T (BE5 BE6 T 3 (3 4 T 4 b b Smlarly for E7 E7 + (4 3 T Th currnt P s th sum of 5 and 7, that can b assum to b qual to th sum of E5 and E7. Thus P T 3 4 T Th currnts 3 and 4 gnrat a voltag across D and D. whch ar qual to th collctor voltag of T3 and T4 and oby th xponntal law: X Unvrsty of Toronto Fall 00

15 EE35 Analog ntgratd rcuts 3 S v 3 T 3 S v 4 T Dvdng: T Usng th abov xprsson n th quaton for P P Fnally, wrtng th last quaton n trms of v, v and Thn v and v ar gvn by: v P 3 / + vv /[( + Thus, th output of th dffrntal amplfr s gvn by: v v o ( ( ( b 3 + h b + h + h vv t s clar that on of th nputs can b us as th AG voltag whl th man sgnal s njctd on th othr nput. Modrn multplr can xhbt a wd bandwdth and a hgh dgr of accuracy, nvrthlss, for non-crtcal applcatons t s possbl to achv accuracs of % usng dscrt componnts. An xcllnt Glbrt cll n ntgratd crcut form wth a bandwdth product of 0 GHz s avalabl from ntrsl orporaton, part numbr HFA30 [0]. + h b b ] v v v v Basc dod attnuator [9] Fgur 4 X Unvrsty of Toronto Fall 00

16 EE35 Analog ntgratd rcuts Fnally, th quvalnt of th JFET attnuator at hgh frquncs s usually mplmntd wth a dod whos bas pont s vard accordng to a control voltag c or a control currnt c. Fgur 4 dscrbs ths tchnqu, th crcut oprats as follows: th currnt AG can not flow nto th rsstor du to th D blockng capactor but t can flow nto th dod, basng t nto th forward rgon. Assumng that th ampltud of v s small such that th dod s kpt forward basd. Th small sgnal dod rsstanc r d and form a voltag dvdr, thus th output voltag s gvn by: v rd v r + Th small sgnal rsstanc of a PN juncton dod s approxmatly gvn by: d T rd f w substtut ths xprsson nto th voltag dvdr quaton and assumd that th valu of s much hghr than r d, th followng xprsson s found: v f th bas currnt AG s proportonal to th nvlop valu of v n, AG K nv (t, thn th output voltag v o can bcom constant dspt of th varatons n v n. For rado frquncy applcaton gnral purpos dods ar not usful and thy ar rplacd by PN dods. A PN dod s a slcon smconductor consstng of a layr of ntrnsc matral contand btwn two layrs of hghly dopd p and n typ slcon. Whn th dod s forward basd, a fnt amount of charg s njctd nto th ntrnsc layr. Ths fnt amount of charg, consstng of lctron and hols, has a fnt lftm (τ bfor rcombnaton occurs. Th dnsty of charg wthn th ntrnsc layr dtrmns th conductanc of th dod, whras th lftm dtrmns th low frquncy lmt of th dvc for usful applcatons [.3]. PN dods bhav as a normal dod for low frquncy valus, but f th frquncy s ncrasd wll abov crtan lvl, dtrmnd by AG T AG v f n n / πτ, th dod bcoms a pur lnar rsstor whos valu can b controlld by a D o low frquncy sgnal. For frquncs at last tn tms f c th ntrnsc rsstanc of th dod can b modlld by th followng quaton [,3]. X Unvrsty of Toronto Fall 00

17 EE35 Analog ntgratd rcuts K Whr K and x ar constants that dpnd strongly on th fabrcaton procss and ar oftn calculatd mprcally. Ths ntrstng proprty of th PN dod allows th dsgn of swtchs, attnuators, modulators and dtctors. Fgur 5 shows th two basc confguratons for F attnuators usng PN dods. Th attnuaton for ach confguraton assumng, that th dod us purly rsstv s gvn by [,3] : X D PN dod attnuator a Srs b Paralll Fgur 5 [,3] A practcal PN attnuator dvlopd by Aglnt Tchnologs s show n fgur 6. t shows a good prformanc from 300KHz to 3GHz [,3,6]. X Unvrsty of Toronto Fall 00

18 EE35 Analog ntgratd rcuts Practcal PN dod attnuator [.3,6] Fgur 6 and provd th D rturn path, whl 4 and 3 provd th approprat mpdanc matchng for th PN dods. Th last componnt of an AG systm s th logarthmc amplfr, though t s only ncludd n hgh prformanc AG systm t s mportant to study ts basc charactrstcs and confguratons. As pontd bfor, an dal dod shows th followng transfr quaton: D S ( D nt whr: S rvrs saturaton currnt n constant btwn and for slcon dods kt T thrmal voltag. q k Boltzman constant rstrctng th opraton voltag n such way that th xponntal trm s gratr than and n, th quaton can b approxmatd as: D f th dod s part of th fdback loop of an opratonal amplfr just as shown n fgur 7, thn, th currnt D can b wrttn as: S D T X Unvrsty of Toronto Fall 00

19 EE35 Analog ntgratd rcuts Thus, D n n D Takng th natural logarthm on both sds and solvng for S T T n ln S Basc logarthmc amplfr [4] Fgur 7 Ths quaton shows that th output voltag s proportonal to th logarthm of th nput voltag. Th man drawback of ths crcut s th hgh tmpratur dpndnc t shows du to th ncluson of S n th transfr functon. s can b canclld by placng a matchd dod (or dod connctd transstor as shown n fgur 8. Logarthmc amplfr wth S cancllaton [4] Fgur 8 Assumng that both transstors ar matchd and opratng n actv rgon, whch constrans n to b a postv valu, th analyss of th crcut procds as follows. XX Unvrsty of Toronto Fall 00

20 EE35 Analog ntgratd rcuts From th xponntal rlatonshp of a bpolar transstor around th bas-mttr junctons of Q and Q, w obtan th followng: and v [(ln T v ln Th collctor currnt of Q s gvn by S v BE (ln v n BE ln S ] S BE T and applyng KL gnorng th bas currnt of Q and assumng that >>v BE -v BE, th collctor currnt s approxmatly gvn by: Thn v can b xprssd as: v T v ln Fnally v s smply v multpld by th gan of th scond amplfr v n + 4 vn T ln 3 Ths xprsson dos not nclud S, thus t shows lowr tmpratur dpndnc than th basc crcut. Th fnal stp s to mnmz th ffct of th thrmal voltag n th transfr quaton of th log amplfr. T ln XX Unvrsty of Toronto Fall 00

21 EE35 Analog ntgratd rcuts Tmpratur compnsatd log amplfr [4] Fgur 9 Th crcut n fgur 9 show a tmpratur compnsatd log amplfr. Th analyss of th crcut procds as follows, s th nput currnt and s thr a scond nput or a rfrnc currnt. Th mttr bas voltag of Q s: v BE T ln S Smlarly, th bas mttr voltag of Q (gnorng th bas currnt s: v BE T ln S Snc both mttrs ar at th sam voltag, w can wrt: T ln T ln S S Th output voltag and ar lnkd through th voltag dvdr form by an T, thn: + + E 0 T ln T T Th tmpratur varatons du to T can b canclld f th tmpratur coffcnt of th voltag dvdr s th complmnt of that of T (approxmatly m/. omplt AG systm Fnally, a practcal AG systm s shown n fgur 0. Ths crcut s ncludd n th dmo board of th PA660 [5,6] of Burr Brown (now part of Txas nstrumnts. Th PA660 s a hgh XX Unvrsty of Toronto Fall 00

22 EE35 Analog ntgratd rcuts bandwdth, hgh slw rat pratonal Transconductanc Amplfr whos transconductanc can b vard by mans of a rsstor connctd to pn. n ths crcut, th nput sgnal s attnuatd by th rsstv dvdr at th nput of th PA660 and convrtd nto a currnt UT. Th output currnt s convrtd back nto a voltag by th scond amplfr PA6. Th pak valu of th output voltag s chckd aganst th rfrnc voltag EF by th dscrt dffrntal amplfr. Th rror voltag s multpld by th gan of th dscrt dffrntal amplfr, appld to th gat of th JFET N5460 and fltrd by th ntwork ( 9 and. Th output transconductanc of th JFET adjusts th quscnt currnt at pn, thus, changng th transconductanc of th PA660 and modfyng th total gan of th crcut. Th procss contnus untl th systm rachs th stady stat. XX Unvrsty of Toronto Fall 00

23 EE35 Analog ntgratd rcuts omplt AG systm [5,6] Fgur 0 XX Unvrsty of Toronto Fall 00

24 EE35 Analog ntgratd rcuts onclusons: AG systms ar part of any wrlss communcaton systm whr a constant output sgnal s dsrd. Th complxty of th AG systm s dtrmnd by th rqurmnts of th communcaton systm, thrfor th analyss, dsgn and mplmntaton can bcom qut dffcult. Nonthlss, th two basc modls showd n ths work provd nough tools to calculat and charactrz th basc paramtrs of th systm and translat thm nto workng crcuts. Th ncluson of som addtonal crcuts, such as a logarthmc amplfr, provds a way of lnarzng th systm. At low and mdum frquncs, FET s workng n th lnar rgon combnd wth a rsstv fdback ntwork provd th bst mthod for mplmntng a varabl gan amplfr, whl kpng dstorton at a mnmum and provdng a wd dynamc rang. At hghr frquncs -MSFET, DGMSFET, Glbrt clls, TA and PN dods provd a bttr prformanc and th advantag that thy can b mplmntd n ntgratd crcut tchnology. For both cass a carful slcton of componnts, bypassng, prntd crcut layout, mpdanc matchng, tmpratur ffcts and layout can play a vry crtcal rol n th prformanc of th crcut. AG systms and crcuts wll contnu to volv as long as wrlss tchnology bcoms fastr, smallr and mor complx. Nw dvcs, crcuts and tchnqus must b studd, dvlopd and mplmntd. XX Unvrsty of Toronto Fall 00

25 EE35 Analog ntgratd rcuts frncs [] J. Smth Modrn ommuncaton rcuts, McGraw Hll Elctrcal and omputr Engnrng Srs, nd Edton, Nw York, 998. [] U. L. ohd, T. T. N. Buchr ommuncaton cvrs: Prncpls and Dsgn, McGraw Hll, Nw York, 988. [3] Slconx nc. Dsgnng wth Fld-Effct Transstors, McGraw Hll, nd. Edton, 990. [4] Analog Dvcs Nonlnar crcuts handbook: dsgnng wth analog functon moduls and 's, Analog Dvcs nc. Norwood, Massachustts, 976. [5] F. D. Waldhaur Fdback, John Wly & Sons, Nw York, 98. [6]. W. Sayr omplt Wrlss Dsgn McGraw Hll,Nw York, 00. [7]. Lcqursh, M. J Hows,. M. Snowdn Dual Gat FET Modllng Mcrowav Dvcs, Fundamntals and Applcatons, EEE olloquum on, 988 Pag(s: / -/7 [8] P.. Gray,. G. Myr, S. H. Lws, Analyss and Dsgn of Analog ntgratd rcuts, John Wly & Sons, 4 th. Edton, Nw York 00. [9] D. L Schllng Elctronc rcuts: Dscrt and ntgratd, McGraw Hll, Nw York, 989. [0] ntrsl orporaton, HAF30, HF Glbrt ll Product Datasht, ntrsl, 000 [] Natonal Smconductor orporaton LXXX arabl Gan Amplfrs Product Datasht, Natonal Smconductor orporaton, 000. [] Aglnt Tchnologs A Low-ost Surfac Mount PN Dod π Attnuator Applcatton not 048, Aglnt Tchnologs, 000. [3] Aglnt Tchnologs Applcatons of PN dods Applcaton Not 9, Aglnt Tchnologs, 000.c. [4] D. A. Namn Elctronc rcut Analyss and Dsgn, McGraw Hll, Nw York, 996. [5] Burr Brown AG usng th Damond Transstor PA660 Applcaton Bulltn, Burr Brown, Tucson Arzona, 000. [6] Burr Brown Damond Transstor PA660 Product Datasht, Burr Brown, Tucson Arzona, 000. XX Unvrsty of Toronto Fall 00