phase margin and poles

[lhlbluesky]

what's the relationship of phase margin and poles?
for a two-pole system(such as opamp),if p2 is larger,PM is larger,too,is that right?
what's the case of p1?
if p1 is increaseed,does PM become larger or smaller?
for a folded cascoded opamp, how to optimize the phase margin and poles?
thanks all for replying.

 

[jiangxb]

PM = 180°-arctan(GBW/abs(p1))-arctan(GBW/abs(p2)).
PM is larger if p2 is larger. in general, p1 is much smaller than GBW, so it don't affect PM. for a folded cascoded opamp, make p2 three times larger than GBW.

 

[Sadegh.j]

The closer the LHP to the imaginary axis, the lower the phase margin. PM is negative for RHP

 

[lhlbluesky]

thanks for reply.

 

[raduga_in]

For a folded cascode the method to increase PM
is to put your internal poles far away from
the output poles .. so size your devices accordingly ..

Raduga