In a two stage op amp,use a resistor in series with compensation capicator .As the resistir increase,the zero will move into the left-plane.sometimes ,this LPZ shift the phase posetive and the phase margin large than 90, then is it still stability?
You bet! For all kinds of negative feedback on Bode plot it's of open loop amp it's should prevent situation when simultaineously gain cross 0 dB and phase equal 180 or more then 180. Thus ever for closed loop configuration with strong negative feedback (unit gain) the circuit remain stable. The phase margin may be more that 90, it correspond stability condition.
Keep in mind that position of poles and zeros may change during large transients. Always verify stability for input voltage step.
In a two stage op amp,use a resistor in series with compensation capicator .As the resistir increase,the zero will move into the left-plane.sometimes ,this LPZ shift the phase posetive and the phase margin large than 90, then is it still stability?
thanks
Have a look at the gain margin as well. Usually when the PM>90deg, gain margin will be very less. It's preferable to have a gain margin of atleast 10db (this is a rough figure, which someone told me.)