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Model parameters unit

Nadidjka

Hello all,

Can someone please tell me what is the unit of the model parameters in cadence? Are the capacitance values measured per unit width or they're just in Farad?

Thank you,

Nadida

  • There is no tool called "cadence", so this depends on which simulator you are talking about, and which model parameter. If you know the name of the model type, and are using spectre, then if you type (say) "spectre -h bsim4" it will tell you the parameters, the default value, and the units.
  • Thanks for your prompt response. I'm using spectre, and I'm interested in knowing the unit of the capacitances of the pch/nch transistors i'm using(cgd, csd...). what does the "-h" represent in your command? . so if the model type is pch_mac, its name is M0, what command will show me the parameters, the default value & the units?

  • If you look at the model file, you should be able to find the definition of the model, and see what "type" it is. If it's called XXX_mac (assuming this is using a particular well-known foundry's naming), then it's  a macro model, and so in itself it is probably a subckt model. In the definition of the subckt, you'll find an instance of a transistor, and then find the model it calls - and you can hunt down the model definition - in the form:

    model pch bsim4 ...

    or similar. If you just type "spectre -h" you'll get generic help on command line options, analyses, and available component types. "spectre -h bsim4" or "spectre -h bjt" will give you help on a specific model type.

    Now you mention cgd, csd, and so these are probably operating point parameters, not model parameters. Still, the units of those are given too in the help (although they are partial derivatives, so may not be quite what you're expecting, if indeed it is the operating point output parameters that you're talking about).

    Note you can also type "spectre -help bsim4"

    Regards,

    Andrew.

  • Thank you for your help. I also found an alternative way to check the units of those capacitances (which are indeed operating point parameters); they're displayed in the results browser (dcOp-dc or modelParameter-info folders)

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