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A Spice simulation question

Discussion in 'Electronic Basics' started by dave, Mar 8, 2006.

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  1. dave

    dave Guest

    I've entered the circuit for a "warble" audio oscillator! Basically the low freq
    (2Hz) part frequency modulates the high freq (1kHz) audio signal. I can see the
    resulting "FM" output.

    In Spice I use

    ..trans 0.001s

    and can use different times for s to see it more compressed etc. However is
    there a way to see the wave say 0.5s into the display? I mean start at say .49s
    and see a few cycles after that. If I use .trans it always starts at zero.

    I don't think I'm explaining this too well... trying again... what I'd like to
    see is a few cycles, say the start of the output, then a few cycles some time
    later (so I can see the FM effect is actually working and measure the period on
  2. w2aew

    w2aew Guest

    The actual syntax might vary by the particular spice implementation,
    but in general the following syntax would apply:

    ..tran [Tstep] [Tstop] [Tstart] [DTmax]

    and the short form (which you used) is:
    ..tran [Tstop]

    Tstep is the plotting increment for the data, not the timestep for the
    analysis. If set to 0, then the plotting increment equals the

    Tstop is the ending time for the analysis.

    Tstart is the starting time to record/save the analysis data. The
    analysis always starts with time=0. If Tstart is blank or zero, then
    the data is recorded from the beginning. If you set this value some
    something non-zero, then the initial results up to this time will not
    be saved. This is the parameter you want to use.

    DTmax is the maximum timestep to use, so you can force a max timestep
    in the analysis, even for when signals aren't changing quickly.
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