Single-Stage Amplifiers

Transcription

1 類比電路設計 ( le-tae Aplifies Ch-Yuan Yan National Chun-Hs Uniesity epatent of Electical Enee Oeiew ead B azai Chapte 3 ntoduction n this lectue, we study the low-fequency behaio of sle-stae CMO aplifies Analyz both the lae-sinal and the sall-sinal chaacteistics of each cicuit, we deelop tuitie techniques and odels that poe useful undestand oe coplex systes An ipotant pat of a desine s job is to use pope appiations so as to ceate a siple ental pictue of a coplicated cicuit The tuition thus aed akes it possible to foulate the behaio of ost cicuits by spection athe than by lenthy calculations 3- Ch-Yuan Yan / EE, NCHU

2 Basic concepts x(t yste y(t Geneally, the chaacteistic of an aplifie is a nonlea function, y(t α 0 α x(t α x (t α n x n (t whee x(t and y(t ay be cuent o oltae Fo a sufficiently naow ane of x, y(t α 0 α x(t whee α 0 can be consideed the opeat (bias pot and α the sall sinal a 3- Ch-Yuan Yan / EE, NCHU Analo desin octaon hat aspects to the pefoance of an aplifie ae ipotant? n addition to a and speed, such paaetes as powe dissipation, supply oltae, leaity, noise o axiu oltae sws ay be ipotant Futheoe, the put and put ipedances detee how the cicuit teacts with peced and subsequent staes n pactice, ost of these paaetes tade with each othe, ak the desin a ulti-diensional optiization poble llustated the analo desin octaon, such tade-offs pesent any challenes the desin of hih-pefoance aplifies, equi tuition and expeience to aie at an acceptable copoise 3-3 Ch-Yuan Yan / EE, NCHU

3 Coon-souce stae with esistie load cheatic nput-put chaacteistic Analysis (:f the put oltae ceases fo zeo, M is off and As appoaches, M bes to tun on, daw cuent fo and lowe 3-4 Ch-Yuan Yan / EE, NCHU Coon-souce stae with esistie load (cont d (:f > G, M is satuation, whee channel-lenth odulation is nelected, and at pot A: Us aboe equation as the put-put chaacteistic and iew its slop as the sall-sinal a, µ nc ( A µ C n ( all-sinal odel fo the satuation eion 3-5 Ch-Yuan Yan / EE, NCHU

4 Coon-souce stae with esistie load (cont d Conside the effect of channel-lenth odulation M, then and ( µ nc ( λ µ nc ( ( λ µ nc Us the appiation (/µ n C (/( and λ / O, then A λ O O ( // all-sinal odel of C stae clud the tansisto put esistance O ( λ 3-6 Ch-Yuan Yan / EE, NCHU Coon-souce stae with esistie load (cont d (3:Fo >, M is the tiode eion, [( µ nc ] f is hih enouh to die M to deep tiode eion, << (, then on on µ nc ( Equialent cicuit deep tiode eion 3-7 Ch-Yuan Yan / EE, NCHU

5 3-8 Ch-Yuan Yan / EE, NCHU C stae with diode-connected load iode-connected NMO/PMO deices Measue the equialent esistance O O b b 3-9 Ch-Yuan Yan / EE, NCHU C stae with diode-connected load (cont d cheatic η η / ( / ( A b Nelect channel-lenth odulation fo siplicity, we hae and hence f the aiation of with is sall, the cicuit exhibits a lea put-put chaacteistic The sall-sinal a can also be coputed by diffeentiat both sides with espect to : ce, then Conside channel-lenth odulation: ( ( n n C C µ µ ( ( η η / ( / ( // // o o A

6 C stae with diode-connected load (cont d iode-connected deice with stepped bias cuent ubtheshold condition nput/put chaacteistic M satuated M tiode 3-0 Ch-Yuan Yan / EE, NCHU C stae with diode-connected load (cont d C stae with diode-connected PMO deice A µ n( / µ ( / p hee channel-lenth odulation is nelected Fo exaple, to achiee a a of 0, and µ n ( / / µ p( / 00 pecifically,, µ n ( µ ( G p G eeal that G G A 3- Ch-Yuan Yan / EE, NCHU

7 C stae with cuent-souce load cheatic M and M opeate satuation ce O O, the a is A ( O O The put ipedance and the iu equied of M ae less stonly coupled than the alue and oltae dop of a esisto The oltae, G can be educed to een a few hunded illiolts by siply ceas the width of M The put ipedance of MOFETs at a da cuent can be scaled by chan the channel lenth, ie, λ / and hence o / Thus, lone tansistos yield a hihe oltae a ce ( /, scal up only lowes The tsic a of the tansisto can be witten as o ( / µ nc, dicat that the a λ ceases with because λ depends oe stonly on than does Note that o deceases as ceases nceas while keep constant ceases o and hence the oltae a, but at the cost hihe equied to ata M satuation 3- Ch-Yuan Yan / EE, NCHU C stae with tiode load cheatic M opeates deep tiode eion The ate of M is biased at a sufficiently low leel oad alue: on µ C p ( / ( b P Note:,ax 3-3 Ch-Yuan Yan / EE, NCHU

8 C stae with souce deeneation cheatic G A G esistance seen the souce path all-sinal equialent cicuit of a deeneated C stae G ( ( b o b o [ ( b ] o o 3-4 Ch-Yuan Yan / EE, NCHU C stae with souce deeneation (cont d C deice with souce deeneation, 0 C deice with souce deeneation, Ch-Yuan Yan / EE, NCHU

9 C stae with souce deeneation (cont d Equialent cicuit fo calculat the put esistance of a deeneated C stae : x i o : x ( b x ( b x : o [ x ( b x ] x Thus, / x [ ( b ] o [ ( b o ] o ce typically ( b o >>, we hae ( b o o [ ( b ] o 3-6 Ch-Yuan Yan / EE, NCHU C stae with souce deeneation (cont d Chane da cuent esponse to chane applied oltae to da The oltae chane acoss is equal to The chane cuent is b b [ ( b ] o // // o That is [ ( b ] o 3-7 Ch-Yuan Yan / EE, NCHU

10 all-sinal odel of deeneated C stae o oo t follows that et us ewite as ( A b bs o o ( b o o [ o ( b o ] o ( b o o ( b o ( G // o b b o o 3-8 Ch-Yuan Yan / EE, NCHU ouce followe (Coon-da stae cheatic nput/put chaacteistic e can expess the put-put chaacteistic as: µ nc iffeentiate both sides with espect to : µ nc ce / η / Also, note that Consequently, ( ( µ C n µ C, thus ( ( ( η n µ C n A ( ( b 3-9 Ch-Yuan Yan / EE, NCHU

11 ouce followe (cont d all-sinal equialent cicuit oltae a s put oltae b bs / ( b As the da cuent and cease, A η b 3-0 Ch-Yuan Yan / EE, NCHU ouce followe (cont d ouce followe us a cuent souce Output ipedance x x b x 0 b b 3- Ch-Yuan Yan / EE, NCHU

12 ouce followe (cont d ouce followe clud body effect Theen equialent // b A b b b b 3- Ch-Yuan Yan / EE, NCHU ouce followe (cont d ouce followe di load esistance A b b O O O O 3-3 Ch-Yuan Yan / EE, NCHU

13 ouce followe (cont d PMO souce followe with no body effect 3-4 Ch-Yuan Yan / EE, NCHU Cascade of souce followe and C stae cheatic A C A F Copaison F C 3-5 Ch-Yuan Yan / EE, NCHU

14 Coon-ate stae cheatic nput/put chaacteistic ( Fo b, M is off and ( Fo lowe alue of, if M is satuation ( µ nc b µ nc ( b Obta a sall-sinal a of µ nc ( b ce / / B η, we hae µ n C ( b ( η ( η (3 As deceases, so does, eentually di M to the tiode eion if µ nc ( b b 3-6 Ch-Yuan Yan / EE, NCHU CG stae (cont d CG stae with fite put esistance 0 o t follows that O b b ( b ( o O O b 3-7 Ch-Yuan Yan / EE, NCHU

15 CG stae (cont d nput esistance o : x b x ( b o, x o [ ( b ] Thus, 0, ( o b ( b o b eplace with an ideal cuent souce, ( o b o o o if ( b o >> b 3-8 Ch-Yuan Yan / EE, NCHU CG stae (cont d Output esistance {[ ( b O ] O } t is siila to that of C Exaple O ( b ( b O O ( b o The a does not depend on 3-9 Ch-Yuan Yan / EE, NCHU

16 Cascode stae cheatic: C CG M : put deice M : cascode deice M, M satuation, b G G Addition of M to the cicuit educes the put oltae sw by at least the oedie oltae of M Fo, M and M ae off,, and b As exceeds, M bes to daw cuent, and dops epend on the deice diensions and the alues of and b, as assues sufficiently lae alues, two effects occu: ( dops below by, foc M to the tiode eion ( dops below b by, di M to the tiode eion 3-30 Ch-Yuan Yan / EE, NCHU Cascode stae (cont d all-sinal equialent cicuit (λ 0 The oltae a is equal to that of a coon-souce stae because the da cuent poduced by the put deice (M ust flow thouh the cascode deice (M Exaple G A G P b ( b P ( b P ( b P ( b P P ( b ( b P P 3-3 Ch-Yuan Yan / EE, NCHU

17 Cascode stae (cont d Output esistance The cicuit can be iewed as a C stae with a deeneation esisto equal to o [ ( b o ] o o Assu b o >>, we hae ( b o o Tiple cascode That is, M boosts the put ipedance of M by a facto of ( b o Cascod can be extended to thee o oe stacked deices to achiee a hihe put ipedance, but the equied additional oltae headoo akes such confiuations less attactie 3-3 Ch-Yuan Yan / EE, NCHU Cascode stae (cont d Cascode stae with cuent-souce load f both M and M opeate satuation, then G and ( b o o, yield A ( b o o Thus, the axiu oltae a is ouhly equal to the squae of the tsic a of the tansistos Anothe appoach G o A G o o o b b o o // // o [ ( ] o o o b o[ o ( b ] ( f we had assued G, then A {[( b o ] o o } b o o 3-33 Ch-Yuan Yan / EE, NCHU

18 Cascode stae (cont d nceas the put ipedance by ceas the deice lenth o cascod o o ( o ce o µ nc, and λ, quadupl only doubles λ the alue of o while cascad esults an put ipedance of ouhly ( o Note that the tansconductance of M (b is half that (c, lead to hihe noise 3-34 Ch-Yuan Yan / EE, NCHU Cascode stae (cont d NMO cascode aplifie with PMO cascode load The hih put ipedance of the cascod load yields a cuent souce close to the ideal, but at the cost of oltae headoo The cuent souce ipleented with a PMO cascode exhibits an ipedance equal to [ ( 3 b3 o3 ] o4 o3 The axiu put sw is equal to ( G ( G G 3 3 G 4 4 Fd the oltae a: G and {[ ( b o ] o o } {[ ( 3 b3 o3 ] o4 o3 }, we hae A The oltae a is appiated as A [( o o ( 3 o3 o4 ] 3-35 Ch-Yuan Yan / EE, NCHU

19 Folded cascode cheatic The stuctues of (b and (c ae called folded cascode staes because the sall-sinal cuent is folded up [ (b] o down [ (c] Note that the total bias cuent the folded cascode stae ust be hihe than that the cascode stae to achiee copaable pefoance 3-36 Ch-Yuan Yan / EE, NCHU Folded cascode (cont d Analysis Fo >, M is off and M caies all of, yield Fo <, M tuns on M is satuation, i µ pc ( As dops, deceases futhe, fall to zeo if Fo this to occu: b and µ ( p C Thus, µ C ( / p M (sat: µ C ( / p < < M is tiode, <,, and µ C ( / p 3-37 Ch-Yuan Yan / EE, NCHU

20 Folded cascode (cont d Folded cascode with cascode load to achiee hih oltae a 3-38 Ch-Yuan Yan / EE, NCHU