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Spectre Error using S-parameter with Multiple Reference Impedances

gwong

Error:Mismatch found between number of data and number of ports

I'm getting the above error when using s-parameter file that has multiple reference impedances: 

#       Hz      S       RI      R       1 1 50 50 1 1 50 50

If I change the line to (single reference impedance for all ports) the following, it works

#       Hz      S       RI      R       50

What's the proper way of defining multiple impedances so Spectre will run.

 Regards,

Gary

  •  Hi Gary,

     

    I'm not sure why you would have an s-parameter file with multiple characteristic impedances.

    Does the Touchstone format handle multiple characteristic impedances (I've never seen this).

    How is this file being generated?

    Spectre assumes one characteristic impedance.

     

    best regards,

    Tawna

  • Gary,

    A quick check with some touchstone data leads me to believe this isn't currently supported (although it is with spectre format s-parameter files). The translator (sptr) also doesn't handle it, as far as I can see.

    So please contact customer support via http://support.cadence.com and then we can proceed to get an enhancement request in to R&D. Or a workaround may be possible with a bit more detailed investigation, maybe.

    Best Regards,

    Andrew.

     

  • Tawna & Andrew,

     

    Thanks for your reply.  I will contact customer support for further assistance.

     

    Regards,

    Gary

  •  Tawna-

    Touchstone files with multiple normalizing impedances are commonly utilized in simultaneous switching noise simulations where the s-parameters in the Touchstone file characterize both signal nets (normalized to 50 ohms) and  PDNs (power distribution nets) which are typically normalized to 0.1 ohms.

     

    Since PDN nets are low impedance structures, choosing a normalization impedance near the net impedance prevents the magnitude of the s-parameters from assuming very small numbers which can provide better numerical robustness,

     -Ray

     

    Raymond Anderson

    Senior Signal Integrity Staff Engineer

    Programmable Platforms Development

    Silicon Technology Group

    Signal Integrity and Package Development Department

    Xilinx Inc.

    San Jose, California  95124

  •  Hi Ray,

    Thank you very much for your post/explanation.  If you'd like us to enhance spectre to handle s-parameter files with multiple normalizing impedances, please contact Cadence Customer Support at http://support.cadence.com and file a Service Request.  The AE on call will file an enhancement request for you (feel free to reference me in your Service Request and I'll assist as necessary).

     

    Best regards,

    Tawna

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