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Design >> Analog Design >> how many Monte Carlo simulation run?
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Message started by chase.ng on Mar 12^th, 2007, 7:24pm

Title: how many Monte Carlo simulation run?
Post by chase.ng on Mar 12^th, 2007, 7:24pm

Hi all,

I am wondering how do you all decide how many simulation run is required in a Monte Carlo simulation so that the estimation is correct?

Thanks and Regards,
chase

Title: Re: how many Monte Carlo simulation run?
Post by fonseca.ha on Mar 13^th, 2007, 3:00am

I would say for you to make an experiement, sweeping the number of runs, and trying and see when do the statistical parameters stop changing.

The approaches that I have seen are:
1. make 30 runs and use 4Sigma of the results as being the 3Sigma of the circuit.
2. Make 100 runs.

Title: Re: how many Monte Carlo simulation run?
Post by chase.ng on Mar 14^th, 2007, 7:47am

Hi,

Correct me if I am wrong, the parameters never stop changing when the number of run increases, their variation will just become smaller and smaller as we increase the number of run, right? . If that is the case, is there anyway we can justify mathematically that at certain number of run, we are confident enough to say that we had enough?

Thanks and Regards,
chase

Title: Re: how many Monte Carlo simulation run?
Post by Andrew Beckett on Mar 15^th, 2007, 6:17am

We now have support in spectre (and in ADE-XL in IC610) for Latin Hypercube sampling in Monte Carlo (see http://en.wikipedia.org/wiki/Latin_hypercube for a description of what this is) - which is a means of making sure that you can more efficiently cover the distribution without needing quite so many samples as you do with a straight random sampling.

This is quite an amusing link too - http://www.gummy-stuff.org/latin-hypercube.htm which covers this. Another one http://mathieu.fenniak.net/latin-hypercube-sampling/.

A bit of googling should be able to give you some more specific answers to your question.

Andrew.

Title: Re: how many Monte Carlo simulation run?
Post by chase.ng on Mar 15^th, 2007, 6:36pm

Hello Andrew,

It seems like a good way to do Monte Carlo simulation with this LHS, but I guess most of us is still going to stuck with IC5141 or so due to PDK support from the foundry, any idea whether it will be available in older version of cadence?

Thanks and Regards,
chase.

Title: Re: how many Monte Carlo simulation run?
Post by Andrew Beckett on Mar 16^th, 2007, 3:42am

Hi Chase,

Well, the capability is in MMSIM611 - so you could use that with IC5141. There's a parameter "sampling=lhs" which can be added to the monte carlo statement in the netlist, but the problem is that the monte carlo GUI doesn't provide support for specifying arbitrary parameters. So I guess the only option is to use Simulation->Create Input Files, edit the input.scs to add sampling=lhs, and then Simulation->Run.

Regards,

Andrew.