Paul
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Hi Faisal,
for CMFB it should be sufficient if you act on the CM voltage in your folded cascode 1st stage while measuring your CM output at the output of the 2nd stage. The following paper shows an example for CMFB in a folded-cascode amplifier:
"A high-speed fully differential CMOS Opamp", by A.Younis, presented at the Midwest Symposium on Circuits and Systems 2000. You can get it from the IEEE website.
There's also some examples in "Design of Analog Integrated Circuits and Systems" by Laker and Sansen, McGraw-Hill in chapter 6. You may find some info in any advanced CMOS design textbook targeting amplifier design.
Paul
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