About the AC result of this amplifier

[gaom9]

Hi, I am designing a full differential OTA which is a Folded Cascode amp.
There is something strange in the AC result.
Can anyone help me analyze it？
Thank you！
The AC result is the OUTP node.

 

[LvW]

Hi, I am designing a full differential OTA which is a Folded Cascode amp.
There is something strange in the AC result.
Can anyone help me analyze it？
Thank you！

When you say "there is something strange" you must have had some expectation about the result, right? So, what did you expect or want? What makes you think that "something" looks "strange"?

 

[gaom9]

Hi, I am designing a full differential OTA which is a Folded Cascode amp.
There is something strange in the AC result.
Can anyone help me analyze it？
Thank you！

When you say "there is something strange" you must have had some expectation about the result, right? So, what did you expect or want? What makes you think that "something" looks "strange"?

Hi, LVM
I am sorry I did not describe the meaning distinctly.
My question is why there is a zero in the AC result at the frequency near the main pole which makes the phase-margin bad.
Because this zero is near the main pole, so I think it is caused at the output node, but I do not know why.
This OTA is used as the boost-amp in a gain-boosted amplifier.
So it should have a good PM.

Thank you!
Best regards!

 

[LvW]

...........
My question is why there is a zero in the AC result at the frequency near the main pole which makes the phase-margin bad.
Because this zero is near the main pole, so I think it is caused at the output node, but I do not know why.
...........
...........
Best regards!

Why do you worry about the zero? It enhances the phase function and, thus, improves stability. Nevertheless, I agree, of course the margin is not sufficient.
But it is impossible for me to locate the source of the zero. Perhaps you should try a kind of classic phase compensation.