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Design Languages >> Verilog-AMS >> Verilog-A: Need to add effect of MOS models
https://designers-guide.org/forum/YaBB.pl?num=1206371813

Message started by hvnmos on Mar 24^th, 2008, 8:16am

Title: Verilog-A: Need to add effect of MOS models
Post by hvnmos on Mar 24^th, 2008, 8:16am

Hi,

How can the effect of different MOS Or Passive models be implemented in a verilog-a model?
For example:
I want to model a resistor. The resistance should change depending on if the passive models are nominal, low or High.
So in case of nominal models resistance should be 1K, for low it shoule be 0.8K and for high it should be 1.2K

Thanks
hvnmos

Title: Re: Verilog-A: Need to add effect of MOS models
Post by Geoffrey_Coram on Mar 24^th, 2008, 12:18pm

Seems like this is not really Verilog-A specific; if you can do it for a built-in resistor, you can use the same technique for Verilog-A models. Eg, using "sections" in spectre libraries to set the sheet rho for the model. You can set up a Verilog-A resistor with a sheet rho parameter, too.

Title: Re: Verilog-A: Need to add effect of MOS models
Post by hvnmos on Mar 25^th, 2008, 1:46am

If, sheet resistance is passed as a parameter. We still would have to change the parameter for a different corner. Or would it get changed on its own.
Is there no possibility, of having a conditional statement included in the verilog-A code that could somehow find out what model we are using and change the sheet resistance value on its own?

Thanks
hvnmos

Title: Re: Verilog-A: Need to add effect of MOS models
Post by Geoffrey_Coram on Mar 25^th, 2008, 5:52am

How do you change the model? Certainly, the V-A model can't read your mind. :) How do the other devices "find out" what model you're using?

In many foundry libraries, you include the library with a statement like this in your netlist:

.LIB '/path/to/file' TT

where TT is for the nominal/typical model, and you use SS or FF for slow and fast. The way the library file is constructed, there are global parameters that are set differently for TT,SS,FF, and the .model cards use these global parameters.

There is no Verilog-A construct for asking which LIBrary or corner (TT/SS/FF) you are using.

Title: Re: Verilog-A: Need to add effect of MOS models
Post by hvnmos on Mar 28^th, 2008, 2:29am

Hi,
I have done following to implement what I wanted:

I have instantiated a spice primitive, a resistor of 1K. Applied a 1V source across it.
Measured the current through that resistor.
Compared it with predefined values, that I would expect. And found out if my resistance is low or High or Nominal.

It works well.

Thanks
hvnmos