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If you are not using any differential output stage with high impedance outputs you don't require CMFB.
You generally don't need such a stage to design a single ended output opamp. So you dont have to worry.
hi saro,
if I design a differential out amplifier, I use cmfb to surpress the common mode noise, do I also have to design bias circuit to fix the input dc point voltage?
CMFB is primarily used to fix the bias points. To suppress the common-mode noise, you need to improve CMRR. I don't see how CMFB can be used to 'improve' CMRR.
I design a single ended error amplifier as a cmfb circuit just like Razavi book describes, but I found that the dc point of differential out just about 50mv below my CM reference Voltage which is VDD/2. It seems the my cmfb circuit can not fix the bias point. What do you think about the problem? thanks.
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