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Reproduce monte-carlo results with changed netlist

Daniel S

Hello,

I have a question regarding the monte-carlo simulation.

I have a monte-carlo run, in which I don’t meet my specifications (for instance run 4). In order to fix the problem, I need to make some changes in my schematic, which results in a changed netlist. But with a changed netlist, the parameter distribution for all elements (transistors, resistors….) get different. So if I simulate run 4 again, I cannot reproduce the failure.

Is there an option, in which I can save the parameter distribution for each specific element, before I change the netlist, so that the “old elements” behave like in the original run 4? 

  • Andrew Beckett

    In the CIW or in your .cdsinit enter:

    envSetVal("adexl.monte" "createStatisticalCornerType" 'cyclic "promptValues")

    You can also set it to "values", "prompt" or "sequence" (sequence is the default).

    You also need to turn on the saving of process and mismatch data on the Monte Carlo options form before you run Monte Carlo to use values-based statistical corners.

    Then once you've run the monte carlo, you can go over point 4 in the results table and do Right Mouse->Create Statistical Corner and you'll be prompted whether you want to create a values-based corner. These then record all the statistical parameters for the devices so that you can re-run that point in single run sweeps and corners mode. With a sequence based corner it just re-runs point 4 again and that's then sensitive to topology changes (when running mismatch) because the random number generator will be invoked a different number of times than previously. Sequence-based corners are only useful if you're only changing the parameters (they're currently more efficient to generate which is why values-based is not enabled all the time).

    Regards,

    Andrew.

  • Daniel S

    Perfect, this is what I was looking for.

    Thank you.

    Regards,

    Daniel

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