Op amp : poles and phase margin

[dinow]

op amp with 60 degree phase margin

Can some body please help me to solve the following question:

An opamp model has three poles at frequencies w1,w2, and w3 and no zeros. Its open -loop unity-gain frequency, wt, is equal to 10^8 rad/s. Assume that w1<<w2 and that w3=100wt. Where should the second pole be placed in order to achieve 60 degrees phase margin?


Thank you for your assistance

 

[gingerjiang]

pi/3=pi-atan(wt/w1)-atan(wt/w2)-atan(wt/w3);
atan(wt/w1)=pi/2;
w2=wt/0.564

 

[122013137]

Agreed with gingerjiang

 

[pz5921087]

Agreed with gingerjiang!!