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Using variable for CDF Parameters in a netlist file

meredith

As a work around for pPar, is it possible to use a variable for a parameter in a CDL netlist file and pass the value of that variable down through hierarchy? 

  • Andrew Beckett

    Why do you need a workaround for pPar? Why can't you just use pPar?

    Regards,

    Andrew.

  • meredith
    The length and width of transistors are combined to use the area of the transistor for comparison in the netlist. Area is defined as a parameter for the transistor but marked as not editable. If pPar is used for the length or width the variable passes to the lower level but the default value is used for the area calculation.
  • Andrew Beckett

    That suggests to me that the area is computed via a CDF callback, which would prevent the use of pPar() or indeed parameterisation of any type on the source width/length parameters. This is a limitation of your PDK - you should take it up with the provider of the PDK.

    If the area had been set in the CDF to be iPar("width")*iPar("length") then it would have worked... but because it is computed via a CDF callback, that's only triggered when  you update the form.

    See The Dangers of CDF Callbacks.

    Regards,

    Andrew.

  • meredith
    Thank you Andrew. Unfortunately the PDK creators are not interested in changing the code that is why I am interested in finding a work around.
  • Andrew Beckett

    One possibility might be to take a copy of the component into your own library, and then use Tools->CDF->Edit, edit the Base CDF of the copy, and remove the callback for the width and length parameters and change the area to be iPar("width")*iPar("length") - or whatever is an appropriate expression. Then use the copy instead of the original PDK device.

    Not sure if that will upset any flow/design review process you might have though...

    Regards,

    Andrew.

  • meredith
    Thank you for going into detail with this solution. I will give it a try and post the results.

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