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Problem when using RFDE momentum blocks in Cadence (Drop across Resistance w/o any current)

dipal261

Hi,

I have a problem with the use of RFDE mom symbol view in Cadence schematic. The image is attached below for reference. The momentum block is basically a MOM capacitor for coupling ac input . In theory, there should not be any drop in the 3KOhms resistance connected to the gate of the transistor in one end and the capacitor on the other end. This entire block works fine if I simply remove the MOM model with an ideal capacitor from analoglib. In that case, I see no drop across the 3K Ohms resistance. But when using the MOM model, it simply destroys any gate biasing that I try to put. What is the problem here? and how can I get a work around it?

This is a dc analysis and shows the current and voltage at each node.

Thank you.

 

Regards

Dipal

Parents

  • Dipal,

    Some questions:

    1. Does the MoM component give you a choice of interpolation method? It would be good if you could pick "bbspice" as this is generally a better choice for passive components. Otherwise you could try using the nport component from analogLib and picking bbspice as the interpolation method, and pointing at the s-parameter file
    2. How low in frequency does your s-parameter file go down to? Does it have a DC point in the file?
    3. What frequency grid did you pick when you ran your Momentum simulation? We would generally suggest a linear sweep and ensure that there are sufficient points.
    4. If you add "-cc" (to clear the cache) on the spectre command line (which you can access via the userCmdLineOptions field on Setup->Environment in ADE), and re-run, does spectre complain about passivity or causality when processing the s-parameter file? Usually this is only done the first time  you use a particular s-parameter file, so the clear cache option forces the checks to be run on subsequent simulations (usually you'd not have this set for best performance though).

    Regards,

    Andrew.

Reply

  • Dipal,

    Some questions:

    1. Does the MoM component give you a choice of interpolation method? It would be good if you could pick "bbspice" as this is generally a better choice for passive components. Otherwise you could try using the nport component from analogLib and picking bbspice as the interpolation method, and pointing at the s-parameter file
    2. How low in frequency does your s-parameter file go down to? Does it have a DC point in the file?
    3. What frequency grid did you pick when you ran your Momentum simulation? We would generally suggest a linear sweep and ensure that there are sufficient points.
    4. If you add "-cc" (to clear the cache) on the spectre command line (which you can access via the userCmdLineOptions field on Setup->Environment in ADE), and re-run, does spectre complain about passivity or causality when processing the s-parameter file? Usually this is only done the first time  you use a particular s-parameter file, so the clear cache option forces the checks to be run on subsequent simulations (usually you'd not have this set for best performance though).

    Regards,

    Andrew.

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