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Spectre skipping points

DavidLou

Hello exports,

I guess I might need some parameters to Spectre to avoid skipping value points. By older version it gives good staircased signal (from VerilogA) but in newer version it misses several stairs. Any clue what I should do to make the simulator not skipping?

the good staircase signal in older Spectre simulator:

the bad staircase signal with several stairs missed in newer Spectre simulator:

thanks,

David

  • Hi David,

    Without knowing anything about the version you're using, the model, the circuit, or the simulation settings, it's virtually impossible to say. However, the delta in the output signal is very small - perhaps it's below reltol (the default reltol on a 5V signal could cause changes smaller than 5mV to be ignored if using reltol=1e-3 and errpreset=moderate) - here your output steps were only 10uV in a 5V signal. So it might be an accuracy control thing, or it could be all number of other issues - there simply isn't enough information to diagnose the issue.

    Regards,

    Andrew

  • in reply to Andrew Beckett

    hi Andrew,

    totally understand and was wondering if some quick clue, not expecting exact answer yet. I guess I might have to create a small test case to reproduce and get back to you.

    P.S., the Important parameter values from prompt:
    start = 0 s
    outputstart = 0 s
    stop = 1 s
    step = 1 ms
    maxstep = 10 ms
    ic = all
    useprevic = no
    skipdc = no
    reltol = 100e-06
    abstol(V) = 1 uV
    abstol(I) = 1 pA
    temp = 27 C
    tnom = 27 C
    tempeffects = all
    errpreset = conservative
    method = gear2only
    lteratio = 10
    relref = alllocal
    cmin = 0 F
    gmin = 1 pS

    thanks,

    David

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