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Can the stb simulation in Spectre calculate the negative phase margin?

zuiying

When I was simulating a two-stage op amp, I tried to use stb to simulate its stability.

 At first I did not add a compensation capacitor (later I used ac simulation and the calculator to find that the phase margin at this time was a negative value).The stb simulation shows "PM metric not found".

And when I added the compensation capacitor, the stb simulation showed the phase margin.

Therefore, can the stb simulation only calculate the positive phase margin, and the negative phase margin will be considered "PM metric not found"? (If this is the case, then I may prefer to use ac simulation and calculators in the future.)

Thank you very much.

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