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#1 Dec 5, 2018
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#### Gain Margin and Phase Margin

Hi,

I have used different measurement formulas from evaluate measurements. Apparently, GainMargin and PhaseMargin needs two arguments. Can't figure out which two it needs.

How to use Gain Margin and Phase Margin formulas from Analog Measurement?

Thanks,

R

Sat, 2018-12-08 09:34
alok
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It needs two arguments - 1st one is Phase Trace

2nd is mangnitude trace in DB

You can get Phase trace by using P() function, example - P(V(Load))

Similarly mangnitude trace in DB can be done by using DB() function Example DB(V(Load))

You can also use Trace > Measurement menu, and Then select GainMargin from measurment list and Click on Eval. This will open a nice little form with description for each argument.

Sat, 2018-12-08 23:16
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Thanks it works.

Thu, 2019-03-28 02:28
janayya
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Hi Alok,

I have tried to measure the GainMargin & PhaseMargin from Bode plot but I could see the following error.

Kind Regards,
Janayya

Thu, 2019-03-28 02:46
RobertoGb
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Hello,

Just consider two things:

- Click on Trace --> Measurements, look for Gain Margin and click on View. You will see that the inputs needed are two. The first one must be the phase of a trace and the second one the magnitude of a trace. In the measurement, the search point in the phase is -180 degrees. If your phase trace does not cross -180, the measurement is not able to find any point, that is why, you will get the error you have shown.

- If you have a phase crossing -180, then remember that the first input in the measurement must be for example P(v(out)) and the seconde input DB(v(out)).

It should clarify.

Regards

Thu, 2019-03-28 03:36
janayya
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Robert, Thank you so much for your suggestion.