phase margin increasing up to 60 degress

[kundahari]

phase margin

Hi all, I designed transimpedance amplifier. it was fine for gain, bandwidth and everything.. but coming to stability analysis..phasemargin is very less.. it was abt to 15degrees..i would like to know what makes it instable ..how to increase phase margin upto 60 degrees.
thanx

 

[LvW]

Re: phase margin

Well, it´s quite normal in analog design to end at a compromise.
If gain, bandwidth,... is satisfying, somewhere is an important parameter which is worse. In your case - stability margin.
I suppose you know why many opamps have relatively low bandwidth (universal compensated).
Consequence: You have to modify the frequency response, no other alternative (lag or lead-lag compensation).

 

[Sadegh.j]

Re: phase margin

What I know is that when you want to increase the phase margin, you have to decrease the unity gain band width.

(I am sure you are using the compensator stage)