Nested Gm-C compensated Opamp

[rishabh_31ec]

Hi, I have attached the circuit of three stage Op-Amp using Nested Gm-C compensation. Could anyone explain what is the exact job of stage encircled by red color, and how can this stage design. Please help.....

 

[erikl]

I think this stage is needed for isolation between input and output of the (-)g_mf1 stage. Find here an example for this circuit with transistor size values (p. 26): View attachment Multistage_Opamp_Presentation.pdf

 

[kenambo]

Hi erikl..

what is the need for this isolation here..

does it need to avoid feedforward voltage..

and how it is done?
thanks

 

[erikl]

what is the need for this isolation here..

does it need to avoid feedforward voltage..

and how it is done?

-g_mf1 is a feed-forward stage!

I'd suggest to study the literature on Nested Gm-C Compensation and Nested Miller Compensation given in the References of the a. m. PDF file.

 

[rishabh_31ec]

Thanx erikl