Continue to Site

# negative feedback and loop gain problem

Status
Not open for further replies.

#### Elhossiny

##### Newbie

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

#### Attachments

• 273473258_243146664701387_2501118764922879138_n.jpg
37.2 KB · Views: 89

Hi,
the open-loop gain decreased and open-loop BW increased and GBW remain constant
with respect to what?

Klaus

Hi,

with respect to what?

Klaus
this analysis and simulation for stb analysis in cadence

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

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?

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).

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?

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.

Status
Not open for further replies.