deciding commonmode feedback for fully differential opamp

[bharat_tangudu]

Hai,

I am designing common mode fully differential two stage opamp. opamp has ben designed whose inputs are fed at NMOS MOSFETs. I have decided to use differential difference common mode feedback circuit (non-resistive). I am confused what type of CMFB would be taken like inputs of CMFB at PMOS or NMOS.
Can someone help me in deciding what type of CMFB will be taken NMOS based CMFB or PMOS based CMFB?

 

[erikl]

... what type of CMFB will be taken NMOS based CMFB or PMOS based CMFB?

Both methods are possible. It depends on the circuit design of the OTA.

 

[bharat_tangudu]

Both methods are possible. It depends on the circuit design of the OTA.

I want to connect the CMFB's output to load of 1st stage of the differential circuit. And CMFB's input is coming from 2nd stage output of differential amplifier.

 

[erikl]

I want to connect the CMFB's output to load of 1st stage of the differential circuit. And CMFB's input is coming from 2nd stage output of differential amplifier.

This is the usual connectivity for every differential amplifier with CMFB.
Find here two lectures about possible configurations.