Hi all, How to plot Phase Margin? I have plot wave...
# sky130a
ALOK PRATAP SINGH
04/20/2023, 7:12 AMHi all, How to plot Phase Margin? I have plot wave. *180*cph(v(vout))* I feel its incorrect. @srinivasan_muthukrishnan19 @Piyush Dwivedi
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Stefan Schippers
04/20/2023, 8:13 AMWhy do you feel it's incorrect? It's an inverting amplifier, so in-band phase is 180deg.
Phase margin is related to a feedback configuration, and is the phase of the feedback loop when loop gain goes down to unity. If at unity gain the phase is shifted more than 180deg (negative phase margin) this means there is a frequency where gain > 1 and phase=0, that means positive net gain and circuit will oscillate.
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Emmanuel Innocent
04/22/2023, 4:17 AMPlease @ALOK PRATAP SINGH is it on Ubuntu 22.04 you did this simulation?
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ALOK PRATAP SINGH
04/24/2023, 4:15 AMyes @Emmanuel Innocent it is 22.04.1
ALOK PRATAP SINGH
04/24/2023, 10:00 AM@Stefan Schippers issue is here, I am getting only one pole it should not go to zero. it should go -90 degree or +90 degree. While increasing frequency I am getting phase plot like this. it should be something like becoming horizontal line after 90 degree.
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Stefan Schippers
04/25/2023, 11:14 AMHere is a simple single pole model (vout2) vs the actual circuit (vout). As you see single pole behaves as you say, phase shifts from 180 to 90. The real system has multiple poler/zeroes. Adding a miller capacitance between vin and vout2 will make the small signal model behave similar to the mos transistor.
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