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avoid local alteration on iterative instances

giopero

hello,

I am running a monte carlo simulation (local mismatch only) and I would like to skip local alteration on iterative instances. 

for example, let us consider a current mirror Imaster<2:1> to Islave<4:1>.  I am interested in treating this mirror as 2 devices only (same as it would be when using m=2 and m=4 parameters) and do not apply local alteration between iterative instance, eg. bteween Imaster<2> and Imaster<1>, since these instance are anyway connected in parallel.

background of the question is to reduce simulation time, due to large input file generation when calling a monte carlo simulation on large circuits where many iterative instances are used. 

thanks, 

Giovanni

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  • Hi Giovanni,

    I don't believe this is possible. I'm not sure it would help anyway (or even be meaningful). First of all the "input file generation" (presumably netlisting) is unaffected by whether you are running with mismatch or monte carlo at all. When simulating with APS, device compaction (combination of parallel devices such as when using iterated instances into an m-factor) which usually happens, does not happen if you are running monte carlo with mismatch, because that would prevent individual variation of each instance. That can't be prevented as far as I know.

    Even if it was possible, the fact that the devices are in parallel does not prevent what the models are actually capturing, which is the remaining local random variation in the devices. The "mismatch" part of the statistical models is not about whether the devices have been laid out using good matching which is a systematic variation, but the remaining random variation assuming good layout practice. So they really ought to be varied anyway...

    If you have a performance issue with monte carlo on a big circuit, please contact customer support - then we can look at what can be done to improve performance.

    Regards,

    Andrew.

  • in reply to Andrew Beckett

    hi Andrew,

    many thanks for your feedback.

    br, Giovanni 

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