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Regarding monte carlo simulations

ag2888

Hi,

I am trying to run monte carlo simulations for my design and see the following trends in it.

The results vary if i add in a circuit which is not connected to the circuit for which the result is being considered.

The results vary even if i add in dummy devices, resistors etc.

If i manually choose the added devices to be ignored, only then the result remains the same.

Is this expected for the monte carlo sims?  

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  • Andrew Beckett

    I assume by "vary", you mean you don't get exactly the same results as without the devices. The variation of all devices should still be within the distribution for parameters, but they are unlikely to be precisely the same run to run if you add additional devices and have mismatch enabled.

    The reason for this is that mismatch parameters are generated by the random number generator for each subckt instance in the circuit. This means that if  you have a different number of devices, this will alter the sequence of the random number generator and so it won't be the same as it was the previous time. If you tell Monte Carlo that mismatch is not to be applied for a set of devices, then the random number generator doesn't get called for those devices and that's why you see the results the same from run to run, even if you add the extra devices.

    So yes, this is expected (if I've understood what you're saying). Generally speaking it shouldn't matter because the results are still within the distributions of the random variables.

    Regards,

    Andrew.

Reply
  • Andrew Beckett

    I assume by "vary", you mean you don't get exactly the same results as without the devices. The variation of all devices should still be within the distribution for parameters, but they are unlikely to be precisely the same run to run if you add additional devices and have mismatch enabled.

    The reason for this is that mismatch parameters are generated by the random number generator for each subckt instance in the circuit. This means that if  you have a different number of devices, this will alter the sequence of the random number generator and so it won't be the same as it was the previous time. If you tell Monte Carlo that mismatch is not to be applied for a set of devices, then the random number generator doesn't get called for those devices and that's why you see the results the same from run to run, even if you add the extra devices.

    So yes, this is expected (if I've understood what you're saying). Generally speaking it shouldn't matter because the results are still within the distributions of the random variables.

    Regards,

    Andrew.

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