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Monte Carlo simulation with verilog-a model using Spectre

yueguoguo

Hi all,

I have written a behavioral model using verilog-a and want to simulate it using spectre.

Additionally, I want to study how the statistical variations of some of the parameters defined in my model affect the overal electrical characteristics, that is, I need to do a Monte Carlo simulation for this study.

I know how to do the Monte Carlo simulation provided with foundry PDK, so my problem is whether can I do the Monte Carlo with the parameters that I defined in my verilog-a model and plot the statistical analysis results as a histogram or something?

Thanks if any of you could lend me a hand on this!

-yueguoguo 

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  • Andrew Beckett

    If I run with your statistics block, I get:

    Warning from spectre during Monte Carlo analysis `mc'.
    WARNING (SFE-3224): Variance of the mismatch parameter `gm_mc' is evaluted to be zero.
    Error found by spectre during Monte Carlo analysis `mc'.
    ERROR (SFE-3225): Variance (or standard deviation) of statistical
    parameters cannot be zero! Set `ignorezerovar=yes' in global options to
    bypass this check.

    This is because you have percent=yes and so the standard deviation is set to be 1% of the mean value (which is 0). That's not going to work.

    There's no need to make the standard deviation a function of an instance parameter. What you would do is have a normalized statistical parameter - e.g. a mean of 0, and standard deviation of 1, and then scale it in the model. In this case your model has a standard deviation of gm (if I remove the percent=yes) because you're multiplying gm_mc by gm. If you wanted it to be 1% of gm, you could write:

    localparam real gm_effective = (1+gm_mc*0.01)*gm; // nominal transconductance plus monte-carlo mismatch effect


    Regards,

    Andrew.

Reply
  • Andrew Beckett

    If I run with your statistics block, I get:

    Warning from spectre during Monte Carlo analysis `mc'.
    WARNING (SFE-3224): Variance of the mismatch parameter `gm_mc' is evaluted to be zero.
    Error found by spectre during Monte Carlo analysis `mc'.
    ERROR (SFE-3225): Variance (or standard deviation) of statistical
    parameters cannot be zero! Set `ignorezerovar=yes' in global options to
    bypass this check.

    This is because you have percent=yes and so the standard deviation is set to be 1% of the mean value (which is 0). That's not going to work.

    There's no need to make the standard deviation a function of an instance parameter. What you would do is have a normalized statistical parameter - e.g. a mean of 0, and standard deviation of 1, and then scale it in the model. In this case your model has a standard deviation of gm (if I remove the percent=yes) because you're multiplying gm_mc by gm. If you wanted it to be 1% of gm, you could write:

    localparam real gm_effective = (1+gm_mc*0.01)*gm; // nominal transconductance plus monte-carlo mismatch effect


    Regards,

    Andrew.

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