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Spectre X vs APS++

I look at the following and it seems spectre X Mx accuracy is close to Spectre APS Moderate (not sure if APS++ has the same %accuracy). When I simulate my post layout differential amplifier, former gives 6mV DC offset, latter gives 0.5mV DC offset, DC analysis.

My question is, which one is more accurate, and I can trust more?

P.S. Spectre Cx also gives the same offset as Mx and I do APS++ with liberal accuracy, with conservative I also get 0.5mV offset!

Andrew Beckett over 2 years ago

Please contact customer support (create a case).

Andrew
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illaoi over 2 years ago in reply to Andrew Beckett

Thanks for the quick respond, Andrew, though, it would be nice if I know your thoughts as well.
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ShawnLogan over 2 years ago in reply to illaoi

Dear illaoi,

As Andrew mentioned, unless you can provide the specific details on your specific simulator settings, it is best to contact support. As an example of an unknown that seems as if it might be responsible for your discrepancy, spectre X by default uses post-layout reduction. Spectre +aps or ++aps does not utilize it by default. Hence, if you did not specifically disable it in your Spectre X simulation, Spectre X and Spectre +aps (or ++aps) may indeed show different DC offset results. My understanding is the "gold standard" used by Cadence to gauge simulator accuracy is spectre without +aps nor ++aps. Hence, you might want to run your simulation in pure spectre to examine its results.

Shawn
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Frank Wiedmann over 2 years ago in reply to ShawnLogan

Postlayout optimization in Spectre X can be turned off with the command-line option +postlpreset=off
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