what is the phase margin in this case?

[princerock]

Hi,

I designed a fully diff op amp with cmfb. And when I did the ac sweep to the cmfb network I got the following result. I am puzzled by the phase response. Is it oscillating? If not, what is the phase margin?

Thank you very much for your help!

princerock

 

[newcpu]

It is oscillating. The phase margin = 180-(the changing range of phase till gain at 0dB).

 

[Sezi]

why is this phase curve climbing so high? r there so many zeros in the transfer func?

 

[Alles Gute]

From the gain curve it seems you have one zero and two pole before unit gain point. And your zero is in right half plane. So it's unstable.