For a differential amplifer: vin+=vic+vid/2, vin-=vic-vid/2

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Presentation transcript:

For a differential amplifer: vin+=vic+vid/2, vin-=vic-vid/2 As vid change, Vs=const Vs is virtual ground. left half = -(right half) Can use half circuit: M2 vin- CL M8 M1 vin+ M7 Vyy vo+ vo- Vs VDD VDD VDD Vyy M7 R,C vo+ vo+ CL CL M1 M1 Can further use quarter circuit for analysis with suitable parasitic R, C:

VDD VDD Telescopic cascode amplifier Quarter circuit: M7 M5 Vyy Vxx M8 M6 VDD M3 M1 Vbb Vin CL Rb Vo vo- vo+ CL M3 M4 Vbb CL M1 M2 vin+ vin- Vs

VDD VDD VDD Vo Vb3 folded cascode amp Vb2 Vb2 Vb3 Vin+ Vin- CL Vb4 Vb1 Vb5 Quarter circuit

Both have the same small signal model VDD M3 M1 Vbb Vin CL Rb Vo VDD Vo Vb3 Both have the same small signal model

a a >1 First take Rs = 0, find TF from vg1 to vo then from TF from vin to vg1, Finally, multiply the two together. Include gs2 Include Cgs2, Cdb1, Csb2 Include ro of I-source if folded a a >1 vg1/vin =1/(1+sRsaCgs1)

To find TF from vg1 to vo: Write KCL at vs, KCL at vo, Two equations, eliminate vs, and solve for vo in terms of vg1  vo/vg1

ro  rds1*Av2 || RL Av(0)  - gm1ro p1 = - w-3dB = -1/roCout GBW = gm1/Cout z1 = +gm1/Cgd1 p2  -1/{(rds1|| rincg)Cs2} p3  -1/RsaCgs1

Design steps: SR, CL  IQ OSR  Veff ranges Ibias or Iref  size current source GBW, CL  gm IQ, gm  (W/L)1, round to nice numbers Feedback to generate VinQ Check Veff, if too large, increase W1, (this leads to over design of gm and GBW) Check Av or ro, if not sufficient, use larger L, and adjust W accordingly to keep the same W/L For cascode structures, modify the steps a little.