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How can improve CMFB GBW?

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castrader

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In my design of 2-stage class AB fully differential OP, ac gbw=25MHz av0=110dB
my cmfb gbw is only 5MHz av0=100dB
I use resistor as cm sensor, and use differential op with diode load as cmfb gain stage, feedback to class AB 1st stage tail current partly.
How to increase CMFB GBW?
 

paley

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it's difficult that making the unity-gain freq of the differential-mode and CMFB loop about equal, because the cmfb loop have more poles than DM loop
 

Alan_Nesta

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maybe you can try another cmfb, like feedback to the load device of the first stage, maybe it is useful.
 

    castrader

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