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Instead of using cmfb circuit to set output dc common mode voltage Why can't we put at dc bais voltage at inverting or non inverting inputs of differential amplifier that way Vocm is set through voltage divider of R1 and R2 using Vbias (vb2 in picture) at inv and noninv input and dc common mode input (vb1 in picture) , this is case in single ended output differential amplifiers enter image description here

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CMFB is a part of differential OpAmp, so there is no need to choose to use it or not: it is always there and always used. It can be adjusted if needed, but not "not used". The reason it is always there was discussed at length here and here

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