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fully differential opamp .. how to calculate cmrr ??

rakesh reddy over 11 years ago

I made this schematic and I simulated this I am getting gain ~40dB and UGB 20Mhz,

I want to do stability analysis for this fully differential ckt ,

And I want to find out

--- CMRR

--- PSRR

---Loop gain (from stability analysis )

How I should use cmdprobe to do stb analysis , please help me ,,

adrew sir ,, can you please provide me a link with an example how to procede ..

rakesh reddy over 11 years ago

here is the cmfg and biasing circuitary ..
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Andrew Beckett over 11 years ago

I already answered some of this in your previous post (it wasn't clear whether you'd read the reply, since you're repeating some of the same questions).
Some info can be found in solution 11179406 on Cadence Online Support. Essentially you're inserting the cmdmprobe (or diffstbprobe if using a more recent version) in the feedback loop(s) of your differential circuit, and then setting the CMDM parameter to either +1 or -1. When specifying the probe on the stb analysis form, point at the cmdmprobe instance and it will set things up appropriately. If using diffstbprobe, it will offer you the choice on the analysis form as to whether you want differential or common mode stability.
Regards,
Andrew.
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