Question Folded cascode opamp design

[suria3]

Hi Guys,

I have designed an NMOS input folded cascode opamp to get a good PSRR with a
open loop gain of 70dB. Now when i measure the PSRR of this opamp in unity gain
configuration, i'm getting a PSRR of -38dB. This is because in the unity gain configuration, when i inject dc of 1.2V at input, the output is showing 1.197V, meaning
the folded cascode have a limited output range. So, it makes sense that the PSRR is low due to lowered open loop gain. When i applied the opamp in a CMFB circuit, the input of the opamp both have 1.2V. So, my question is, at this time, can i say that my
folded cascode opamp have a good PSRR due the open loop gain is not degraded. I'm saying this because in unity configuration, when i lowered the dc voltage to 0.95V at input, the output also show 0.95V and the PSRR is -68dB.

Thanks,
Suria

 

[getusoon]

please please can you post a pic of your design. It so happens I have a thesis with lots of parts of which a beginning one involves designing a folded cascode with similar specs but I can't get it to work properly. I have worked out all the other stages but somehow my folded cascode is giving very very low gain.

Thanks a lot in advance.