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how to rise phase margine?

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sadeghbiabani

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how to rise phase margine?
I need increase PM and I can reduce just unity gain BW, not anymore change.what should I do?
I have 63dB gain,40degree PM,800 MHz Unity Gain BW from fully diff Folded Cascode with CMFB(gm constant by level shifter).
every thing is OK but PM is too low.
 

Increase the compensation capacitor.
 

Simply you want your pole to start decaying by the 20dB after a longer time than your current situation so that the PM improves ...as the phase plot will not be affected in the average ....so increase the Cc as mentione by godfreyl ....u can also do it using parametric analysis to understand this effect correctly
good luck :)
P.S. u have to be sure that the Cc pole is a dominant pole
 

in folded cascode compensation capacitor and load capacitor is same.so you must use positive fedback gain circuit.it cause high unity gain frequency and nice Phase Margine.

- - - Updated - - -

if you want increase the campensation capacitor,unity gain will be decrease.
 

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