Question about differential amplifier resistor

[gggould]

Hi,
Does anyone know how are those 2 resistors in the middle helping performance? And how to choose the proper values?

https://obrazki.elektroda.pl/4548811900_1410668669.jpg

Thanks.

 

[Dominik Przyborowski]

This two resistors forming a local common mode fedback setting constant gate potential for M0 and M1.
The better AC performance is obtained by setting R value below 1/gm0 - this moving pole bounded with cgs of M0, M1 in higher frequencies.

 

[esp1]

hi,
Dominik has explained the function of those resistors, you may also find this LTSpice sim of your circuit interesting.

The maximum signal amplitudes occur at the maximum resistor values.

E

 

[gggould]

Thanks for the response Dominik and esp1. That is very helpful.

So another follow up, how does the original circuit different from this one, from cmrr and psrr point of view?
https://obrazki.elektroda.pl/1785936900_1410889835.jpg