What is the phase margin and gain margin for this circuit?

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Homework Help Overview

The discussion revolves around understanding phase margin and gain margin in the context of a circuit analysis problem. Participants are exploring how to visualize these concepts on a plot, particularly in relation to phase shifts and gain levels.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants express difficulty in visualizing the phase margin and its relationship to the gain margin. There are questions about how to interpret the phase shift at the 0 dB gain frequency and what implications arise when the gain margin is negative.

Discussion Status

There is an ongoing exploration of the concepts, with participants questioning their understanding and the relationships between phase margin and gain margin. Some guidance is being offered regarding the implications of negative margins, but no consensus has been reached on the answers.

Contextual Notes

Participants note that the problem is not strictly a homework question but rather preparation for an exam, which may influence their approach and the depth of their inquiries.

Cocoleia
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Homework Statement


upload_2018-4-14_15-57-58.png

The Attempt at a Solution


I am having trouble visualizing this. So I know that the phase margin is how much phase lag it would take to make -180 phase at the 0 dB gain frequency. I am just having trouble placing this on the plot. It isn't a homework question I am preparing for an exam. I would think the answer is 45 degrees ?
 

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Cocoleia said:

Homework Statement


View attachment 224055

The Attempt at a Solution


I am having trouble visualizing this. So I know that the phase margin is how much phase lag it would take to make -180 phase at the 0 dB gain frequency. I am just having trouble placing this on the plot. It isn't a homework question I am preparing for an exam. I would think the answer is 45 degrees ?
Notice that at 180 deg phase shift the gain is still > 0dB!
 
rude man said:
Notice that at 180 deg phase shift the gain is still > 0dB!
I'm not sure what I am supposed to looking at to figure this out then
 
If gain margin is negative, so must phase margin be, making what your answer?
 
rude man said:
If gain margin is negative, so must phase margin be, making what your answer?
So then my answer would be none of the above so it can be negative ?
 
Cocoleia said:
So then my answer would be none of the above so it can be negative ?

That's my vote.
 

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