negative feedback and loop gain problem

[Elhossiny]

I have a problem in this circuit when I simulate its loop gain on cadence
the open-loop gain decreased and open-loop BW increased and GBW remain constant

 

[KlausST]

Hi,

the open-loop gain decreased and open-loop BW increased and GBW remain constant

with respect to what?

Klaus

 

[Elhossiny]

Hi,

with respect to what?

Klaus

this analysis and simulation for stb analysis in cadence

 

[Elhossiny]

common source gain move from loop gain and add to BW.

 

[LvW]

I have a problem in this circuit when I simulate its loop gain on cadence
the open-loop gain decreased and open-loop BW increased and GBW remain constant

I don`t understand the meaning of this sentence.
What do you mean with "open.loop gain"? Is it the gain of the opamp without feedback?
Why do you speak about the "open-loop gain" while simulating the "loop gain"?
More than that - "decreased" in comparison to which other gain?

 

[Elhossiny]

i expect the LG= Aol(first stage)*Aol(second stage), and BW limited to OTA BW.
when i simulate i found that LG= Aol(first stage only) and BW= BWota *(Aol second stage "common source).

 

[crutschow]

I have a problem in this circuit when I simulate its loop gain on cadence
the open-loop gain decreased and open-loop BW increased and GBW remain constant

How is that a problem?
What do you think should happen?

 

[LvW]

i expect the LG= Aol(first stage)*Aol(second stage), and BW limited to OTA BW.
when i simulate i found that LG= Aol(first stage only) and BW= BWota *(Aol second stage "common source).

How did you simulate the loop gain? Did you take care of the correct bias points?
More than that - the diagram shows an opamp, but you always are speaking about an OTA.