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A Spice simulation question



Jan 1, 1970
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


Jan 1, 1970
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.