ywguo
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Glaicer,
I am not familiar SpectreRF. But I have a simple method. Make a CMFB macro model using R, C, and controlled voltage source, although it is not very accurate.
.SUBCKT CMFB_G7 P1 P1D P1DB P2 P2D P2DB CBIAS CMC CMO VDD VON VOP VSS R1 CMC CMO1 200E3 R0 CMO2 CMC 200E3 V1 CMO 0 1.65 E1 CMO1 0 VOL='V(cbias)-(V(cmo)-V(VOP))' max=3.3 min=0 E2 CMO2 0 VOL='V(cbias)-(V(cmo)-V(VON))' max=3.3 min=0 C2 VON CMC 125E-15 C0 VOP CMC 125E-15 * END OF SUBCIRCUIT DEFINITION. .ENDS CMFB_G7
where VOP and VON are the differential output of an opamp, CMO is the bias for common mode voltage, CBIAS is the system bias for tail current, CMC is tied to the tail transistor in the opamp.
Best regards, Yawei
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