T-model: - + v o. v i. i o. v e. R i

Transcription

1 T-mdel: e gm - V Rc e e e gme R R R 23

2 e e e gme R R The s/c tanscnductance: G m e m g gm e 0 The nput esstance: R e e e e The utput esstance: R R 0 /c unladed ltage gan, R a g R m e gmr e 0 m e g me e/e 0 a g 24

3 a g g m e e/e 0 αο gm me αο m Snce, e, then a g m g F the cnfguatn: F the cnfguatn: β R π g m R α e gm R _ > R _ R α R β β R _ a_ a a α β < a _ a α a a β β _ In tems f /p esstance and cuent gan, the amplfe pefms bette than. 25

4 mmn-mtte μ mmn-ase π π μ gmv mmn-ase π R e gm e gmv μ μ π μ μ ο R µ s between -. At hgh feqs., capacte cmpnents ae dmnant. F, µ s between /p and /p. Hence, at hgh-feqs., thee wll be a feedback fm /p t /p. F, /p s at and /p s at. Theefe, µ wll nt cause a feedback at hgh-feqs. ccuts ae used f hgh-feq. applcatn. 26

5 Untl nw we hae assumed that b s neglgble. In pactce, b has a sgnfcant effect n G m and R when the stage s peated at suffcently hgh cuent leels. e e e gme R b b R R The s/c tanscnductance: G m e m g e 0 b KL at, e b g m e e b m e e g b e b -gme e b G gm m -gm b e 27

6 Fm quatn (3.29), g m e π G gm m g -g m m b π m b e g m g π mpang ths wth the tanscnductance f the ccut f b s neglected (.e. G m g m ) shws that G m becmes lwe when b s ncluded. π e e e gme R b b R 28 R The nput esstance: e e m e b e m b -g -g e e b R e e e e

7 -g -g R e e m e b e m b e e b e e e e R -gm b e e Snce g m π and e e 29 m g α, then R g -g α b m m π b gm π gm mpang ths wth the nput esstance f the ccut f b s neglected (.e. R α ) shws α gm that R becmes lage when b s ncluded. At hgh cuent leel,.e. I, π as V β β π T. S, f gm I π s small enugh that t s cmpaable wth b, then b shuld be ncluded n the analyss. xample: If b 00 Ω, β 00 and I 26 ma, then β 00 26m π 00Ω. Hence, gm 26m π b when I s hgh.

8 In cnfguatn, R R In cnfguatn, R R // If R, R _ and R _ Unde ths cndtn, R _ > R _ esdes usng the as hgh feq. amplfe, t can als be used as a cuent suce whse cuent s nealy ndependent f the ltage acss t (.e. g m e ) mmn-gate (G) cnfguatn. V DD R D 30

9 V DD R D I/p sgnal s appled t the S. O/p s taken fm the D. G s cnnected t the ac gnd. The analyss f G amplfes can be smplfed f the mdel s changed fm a hybd-π t a T- mdel. ο S gmgs D S ο D gm bs ( gm g ) The bdy () s ac gnd, bs gs because G s als at gnd. sg 3

10 s ο d s ( gm g ) ο sg d ( gm g ) sg ( gm g ) sg Fgue (b): Nde : S (g m g ) sg Nde 2: d (g m g ) sg Fgue (c): Nde : S (g m g ) sg Nde 2: d (g m g ) sg qual cuents ae pushed nt and pulled ut f the G as the equatns that descbe the peatn f the ccuts ae dentcal. 32

11 s ο d ( gm g ) sg ( gm g ) sg s ο d ( gm g ) sg sg ( gm g ) ( gm g ) sg If s fnte, the ccut s blateal because f the feedback. If, the cct. s unlateal. F : sg ( gm g ) ( gm g ) sg R D 33

12 S sg ( gm g ) ( gm g ) sg R D G D ( m ) g g G g g sg m m sg 0 R g g sg m R R 0 D ( gm g ) sgr a d 0 sg a ( ) g g R ( g g ) 0 m d m sg sg gm g ( g g ) m g m g 34

13 3.3.6 mmn-cllect () cnfguatn (mtte fllwe) V R S s V IAS I c R L V R S s gm β π ο R I/p sgnal appled t the. O/p sgnal taken fm the. R R L 35

14 R S s gm β π ο R R L R S (R S π ) π R / Hence, ths ccut s nt unlateal as the nput esstance depends n the lad esst R L and the utput esstance depends n the suce esstance R S. T detemne R : R / β R L 36

15 R S s gm β π ο β R L ( β )( ) π R L R β π RL R L β π RL RL R R R L enugh. 37

16 R β π RL RL β π RL F R wth n lad,.e. R β π R R L, T detemne a : R S s gm β π ο R R R L Oeall ltage gan: a / s 38

17 R S s gm β π ο R R L R At nde, s g m s R π RL s ( s ) g π m R R R R s π s π L s π Snce g m π β, s β ( s ) ο R R R R s s π s π L s π β β R R R R ο ο s π s π R L s π s π 39

18 a ( β ο ) R s π s β R ο L Rs π ( βο ) π s π L ( βο) ( βο) ( ) L ( ) ( βο ) R ( R s π)( RL ) ( βο ) R 40 ο L s π s π s π L enugh. β R R Rs π R s R R R R R ( R s π) ( β ο) L L // R Open-ccut eall ltage gan, a s L ( R R s π ) β ( ο)

19 a ( R s π) ( β ο ) L // R If the esstance, b, s sgnfcant, t can be smply be added t R S n the expessn. Fm the a expessn, a wll always be less than unty. If ο ( R ) β L // >> R s π, then a. Ths means that the utput sgnal fllws the nput sgnal. Hence, ths tplgy s als knwn as the emtte fllwe. If π >> R S, β >> and >> R L, then a ( β ο ) π RL Snce g m π β, then a gmr L g R m L ( gmr ) L 4

20 R S s gm β π ο R R R L T detemne the sht ccut cuent gan, a : a 0 g m π g m π g ( mπ a ) gm π β g m g m π β β ( β ) a / β 42