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interpolation for xmin calculation

RobinCommander

As an addition to phase margin & gain margin in some AC open loop simulations I have been also been calculating the vector margin which can be useful.

I calculate it thus:

stb_x = xmin((abs((v("/Ampout" ?result "ac") - complex(-1.0 0.0)))**2))

stb_dB = (- db20(value(v("/Ampout" ?result "ac") stb_x)))

To get more accurate results I need to add more points/decade which can slow things down in swept simulations, I assume this is because only the data points are used in the xmin calculation. I was wondering if interpolation could somehow be used in the xmin calculation so I can speed up the simulations. Or maybe there is some other way of doing this calculation.


Thanks,

Robin

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  • p.s.

    I think the formula I gave above isn't really the Vector Margin as it measures the distance
    to the origin not to (-1,0).
    I think it should be:
    VectorMargin = abs(value((v("/Ampout" ?result "ac") - complex(-1.0 0.0)) stb_x))
    I've also seen this called stability margin. Recommended values I've seen are >= 0.33 to 0.5.

    A related measure is Vector Gain Margin which is somewhat similar to gain margin.

    VectorGainMargin_dB = db20(1 - abs(value((v("/Ampout" ?result "ac") - complex(-1.0 0.0)) stb_x)))

    You can also calculate Vector Phase Margin, although I'm not sure how useful that is:
    VectorPhaseMargin = value(phaseDeg(v("/Ampout" ?result "ac")) stb_x)

    Regards,

    Robin

Reply

  • p.s.

    I think the formula I gave above isn't really the Vector Margin as it measures the distance
    to the origin not to (-1,0).
    I think it should be:
    VectorMargin = abs(value((v("/Ampout" ?result "ac") - complex(-1.0 0.0)) stb_x))
    I've also seen this called stability margin. Recommended values I've seen are >= 0.33 to 0.5.

    A related measure is Vector Gain Margin which is somewhat similar to gain margin.

    VectorGainMargin_dB = db20(1 - abs(value((v("/Ampout" ?result "ac") - complex(-1.0 0.0)) stb_x)))

    You can also calculate Vector Phase Margin, although I'm not sure how useful that is:
    VectorPhaseMargin = value(phaseDeg(v("/Ampout" ?result "ac")) stb_x)

    Regards,

    Robin

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