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Distributed Components in QPSS Shooting Engine

illaoi

I see the following error when I am running QPSS while having multiple n-ports

  ERROR (SPCRTRF-15161): Distributed Components are not supported directly for Pdisto analysis with Shooting engine. 1) Firstly, it's recommend to use Harmonic Balance engine for Distributed Components; 2) Or else, for this case and with Shooting engine, try the Rational Fitting Technique(set interp=rational) for NPORT components.

I saw a relevant post but for PSS 

PSS shooting with s-parameter file - Custom IC Design - Cadence Technology Forums - Cadence Community

My question is do I need to change one by one on (maybe there is a smarter way) all n-ports to rational and the options for interpretation methods are linear, spline, and bbspice, which one corresponds to rational? spline and bbspice I suppose?

Spectre 21.1.0.389.isr8 


  • Andrew Beckett

    First of all, do you really want to be using the QPSS analysis with shooting? The main application for this is with switching circuits, where the main tone (the "large" tone) is very nonlinear and then you have a weakly nonlinear second tone. I wouldn't tend to expect such circuits with s-parameters in very commonly. Can you use harmonic balance instead? (you can do this with the "harmonic balance" mode of QPSS, but better still would be to use the hb analysis directly (as there are a few features of harmonic balance which are provided through hb which aren't there through the qpss interface).

    Secondly, that error message is out of date and incorrect. It should not mention interp=rational as that is obsolete. I've filed a change request to get that fixed. Instead however, if the nports either leave the "Interpolation Method" set to "default" or are set to "bbspice" then it will work (bbspice is a more modern rational method that works with QPSS).

    I believe your problem will only occur if you have the nport components already set to explicitly use linear or spline (both are convolution-based methods rather than using a rational approach that you get with bbspice). You'll simply need to fix the schematic for each nport.

    Andrew

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