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AC analysis in hspice

Discussion in 'Electronic Design' started by [email protected], Dec 19, 2006.

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  1. Guest

    Hello All,

    I was wondering if there was a specific method of doing .AC analysis at
    a specific moment in time. I.e you are doing a transient analysis from
    0 to 2us and you need to AC analysis at the 1us mark because that's
    when a tranistion occurs and you wish to know the stability at that
    point. I ask because my circuit has dynamic biasing points and thus the
    gain is different during transitions vs the steady state value but I
    can't find the change.

    Usually when you do the AC analysis it's at time=0 and not helpful for
    me. Is it possible to do a .SAVE at the time I am interested and then
    do a LOAD and then start an AC analysis? How would hspice know to use
    the conditions specified in the LOAD file?

    Variations in gain affects my phase margin which is causing ripples and
    I can't find out without doing an AC at that point.

    Thanks again for any help
  2. Guest

    Even if you can do this, I'd suggest testing the loop with a step
    response. Find a spot to inject a current step in the loop and watch
    the loop settle. Use current since a current source is infinite
    impedance and won't effect the time constants of the circuit. Use all 4
    parameters on the .tran line, i.e force a time step.
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