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how to set up min value for capacitor from analogLib

mbchang

I want to have a minimum value of the cap, but not sure how to set it up. I found below from the spectre manual but I wonder how can we do it from schematic. 

Polynomial capacitor parameters:
13 coeffs=[...] Vector of polynomial capacitance coefficients.
14 symmetric=none Use symmetric resistor model. Possible values are none and absolute.
15 min (F) Minimum capacitance.
16 max (F) Maximum capacitance.

Thanks,

Jerry

  • Andrew Beckett

    Hi Jerry,

    These are only available as model parameters for capacitor, and not as instance parameters. So you'd have to specify this in a model file (e.g. models.scs) :

    model mycap capacitor min=XX max=YY coeffs=[...]

    and then refer to this in Setup->Model Libraries, and fill in the model name on the analogLib cap as being "mycap".

    Regards,

    Andrew.

  • mbchang

    Andrew,

    Thanks for your reply. I did the following and I want my cap clamps at 2u. But somehow when I looked at the result, it didn't do the clamp part (on the left of the plot, the min goes to 1u).

    Any ideas?

    thanks,

    jerry

    model mycap capacitor min=2u coeffs=[-0.048 9.7e-4 -8.73e-6 2.91e-8]

  • Andrew Beckett

    Jerry,

    I can't see your picture, but I tried this:

    // test min and max
    model mycap capacitor min=2u max=2.7u coeffs=[-0.048 9.7e-4 -8.73e-6 2.91e-8]

    C1 (n1 0) mycap c=3u
    V1 (n1 0) vsource dc=1

    save C1:cap
    dc dc dev=V1 param=dc start=0.1 stop=15 step=0.1

    (I set max as well to see if the problem was just the minimum). I get this:

    So I too see that it's not limited by the min and max. Probably best if you report this via customer support, but I filed CCR 1545206 for this issue.

    Regards,

    Andrew.

  • Andrew Beckett

    Just to let you know that this has now been fixed - it will be in the MMSIM15.1 ISR4 hotfix, due out on approximately 8th April. Here's what the curve looks like now (I just tested it):

    Regards,

    Andrew

  • mbchang

    Andrew,

    That's great. Thanks for letting me know. I will test it once it is available to us.

    Regards,

    Jerry

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