two question about Opamp:---CMFB bandwidth & bias circu

[wateror]

hi,
How to set the bias circuits current in the low power circuits design.? I want to set it as small as possible. but matching is an issue if it is too small. so what is the optimization value?

another question is about the GBW of the common mode feedback circuits. do we need to make the GBW of CMFB circuits higher than the differential loop?

thanks so much

 

[hmsheng]

Too small bias current will not help you to save much power because the main power consumption is due to the main circuit, not bias.
The GBW of the CMFB circuit will impact the settling time of the feedback loop. Concider to the stability issue small GBW is better.