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Gain boosting circuit design

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jingxuelu

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gain boosting circuit

I have a question on gain boosting circuit, for the differential OTA, you need use CMFB circuit, however, so what the gain boosing amplifier in the differential OTA, they are basically differential amp as well, so do they need CMFB to set the correct CM level?
 

yes,if you use full diff amp as gain boosting cell,you should add cmfb part
 

Thanks.

Added after 1 hours 43 minutes:

Is it really necessary? I didn't add CMFB for the boosting cell, and it works. In my opinion, the gain boosting celling is negtive feedback for both differential signal and commom mode signal, so it is not necessary to add CMFB, am I right?
 

No! in simulation, the circuit maybe operate.
But you must use CMFB for fully differential amplifier.
Or you can use it without CMFB in case of single ended gain booster.
 

the CMFB is taken in fullly differential amplifier in order to make it work in a stable state. otherwise the commom working point will be drifting .
 

iiiiisland said:
the CMFB is taken in fullly differential amplifier in order to make it work in a stable state. otherwise the commom working point will be drifting .
Click to expand...

That's the exactly spirit of CMFB!
 

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