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#1 Aug 27, 2019
KJL
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Monte Carlo with different positive and negative deviations?

I'm trying to run a Monte Carlo analysis, where the positive and negative deviations of some resistors and capacitors are not the same (ex: the positive deviation might be 1%, and the negative deviation might be 5%). I've tried a few things so far:

1.) I've tried using the resistors and capacitors from the ANALOG library, but they only have a single TOLERANCE value. While I am able to run a Monte Carlo analysis when I give the components a tolerance, I can't determine a way to add both a positive and negative tolerance, meaning both of them have to be the same.

2.) I've tried using the resistors and capacitors from the BREAKOUT library, and editing the PSpice model to include "DEV = 1%/5%". However, upon running the Monte Carlo simulation, it appears that the intended positive tolerance is used for both directions. So, if I put "DEV = 1%/5%", it will give me a +/-1% deviation. If I put "DEV = 5%/1%", it will give me a +/-5% deviation. Once again, it seems like I can't add a different positive and negative tolerance.

3.) I've tried using the resistors and capacitors from the PSPICE_ELEM library, which have both POSTOL and NEGTOL values. However, even when I put a value in for each of these, running the simulation results in the Monte Carlo analysis being skipped, because "no models had tolerances." It doesn't appear to recognize POSTOL and NEGTOL, treating them both as tolerances of 0%, even if I add in another component with a tolerance just to get the simulation to run.

So, now I'm starting to wonder if it's possible to run a Monte Carlo analysis, with different positive and negative deviations. Is there a way to do this?

Wed, 2019-08-28 10:51
oldmouldy
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You need the PSpice Advanced Analysis Option Monte Carlo function to support POSTOL and NEGTOL, regular PSpice A/D just uses DEV and LOT tolerances which are symmetrical.

Wed, 2019-08-28 11:02 (Reply to #2)
KJL
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I thought that's what I was using, but I may be wrong... The method shown in this video is what I've been using. I can also pull up the Monte Carlo window from the PSpice > Advanced Analysis tab, and import measurements from the simulation into there.

https://www.pspice.com/resources/video-library/pspice-advanced-analysis-monte-carlo-analysis-application

Wed, 2019-08-28 11:56
oldmouldy
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The video shows the PSpice A/D Monte Carlo, that does give a message that the "Monte Carlo will be skipped" if the POSTOL and NEGTOL properties are used since PSpice A/D only handles DEV and LOT tolerances for Monte Carlo. You need to add a Measurement to the results of the PSpice Simulation in the Probe Window, like Bandwidth, or whichever Measurement you are interested in measuring the effects of tolerance on, then Start Advanced Analysis, PSpice>Advanced Analysis>Monte Carlo, then import the Measurement from the simulation, then run the Monte Calo within Advanced Analysis. Set the Cursor Min and Max for your performance limits and the Yield % will be shown in the Statistics.

Wed, 2019-08-28 12:01 (Reply to #4)
KJL
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Oh, okay, that makes sense. The video description made it seem like the method shown was already an Advanced Analysis simulation, so I didn't know it was only the A/D Monte Carlo. Thank you!

Wed, 2019-08-28 12:09
ronaks
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