Hello,
Very difficult to ans, in fact phase margin is based on  small signal metric. But once if starts oscillating there is it would leave small signal regime and rest i can't predict, i guess it reaches very near to vdd and vss.

One more thing, according to linear system theory If Phase margin is -ve then pole will be in RH plane hence response would go in exponential increasing amplitude sinusoidal way and mostly it will touch rails and gain will drop down.

Thanks,
Raj.

hello raj can you please elaborate the reason of the negative margin
?
i always find it hard to understand?

xianweng wrote on Sep 1^st, 2013, 9:16am:


When the PM is negative, there will be a lower frequency fo that exhibits a PM=0 deg.
This is the frequency where oscillations might occur. However, it depends on the loop gain magnitude at this frequency if you can observe oscillations or some other kind of instability.