Hello,
How can we calculate PSRR for a ring oscillator(which is realized using MOS)?

Thank you

 

The standard definition of PSSR is the log ratio of change in output voltage to change in input voltage of e.g. an operational amplifier or a voltage regulator.
This useless in your case. You are most probably interested in the change in oscillator frequency as a consequence of change in supply voltage. You can easily calculate the ration dFosc/dVsupply and use this as a definition for PSSR in your case. Note that unlike with voltages you cannot express this ratio in decibels because dFosc/dVsupply has a unit (Hz/V) wheras PSSR for an amplifier is unitless (units cancel when cyou calculate dVout/dVsupply).

I'm not sure whether that's the official definition - I know of none other.

 

A good place to start:

Power supply rejection ratio - Wikipedia

en.wikipedia.org

 

@kiltmr

Not sure why I didn't Google around a bit more before asking, but this was helpful thank you.