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Error evaluating parameter expression with other parameters

GT20260122746

Hello, 

I am having some trouble understanding how to correctly implement some expressions in the parameters in my subckt model.

I have a model that I have defined as a subckt. To begin with, I defined the parameters on the circuit level, like:

simulator lang = spectre

parameters a = 100

parameters b=10*a

subckt test (N1 N2)

test_R (N1 N2) r=b

This works as expected, I can run simulations with the model and they work as expected. However, then when I create a symbol from this and add it to the schematic, I cannot edit the parameter a as it doesn not appear in the property editor, I can only edit the parameters directly in the spectreText file. So I add the parameters into the subckt, like:

simulator lang = spectre

subckt test (N1 N2)

parameters a = 100

         + b=10*a

test_R (N1 N2) r=b

This has the desired result, the parameters appear in the base CDF. I see them in Component Parameters. I can edit them on the schematic editor. However, when I run simulations, it netlists OK, but I get errors:

ERROR (SFE-1997): "input.scs" 14: Cannot run the simulation because xx: parameter `b': Unknown parameter `a' has been specified in expression `10*a', correct the expression and rerun the simulation.

Things I have tried:

  • Changed the parameter a to 'Evalution mode=number', and b to 'Evaluation mode=expression'. This results ina slightly different, but similar error. 
  • Looked around the forums which seems to suggest I might need to turn on ParseAsCEL or something? But I cannot see this option in my Edit CDF menu.

My overall goal is to use multiple instances of this symbol/model, with slightly different parameter values, so perhaps I am going about this the wrong way. 

  • Andrew Beckett

    Not sure exactly how you have things set up. It should work fine in Spectre - this works for example (your example must be wrong, because there's no component name for test_R):

    //
simulator lang = spectre

subckt test (N1 N2)

parameters a = 100
         + b=10*a

test_R (N1 N2) resistor r=b

ends test

I1 (a 0) test a=150
V1 (a 0) vsource dc=1

dc dc
inst info what=inst where=screen

    Anyway, what does the actual netlist look like from ADE? That would give a clue - plus show what you have in the CDF. At the moment, the problem probably is in the part you've not shared...

    Andrew

  • GT20260122746
    in reply to Andrew Beckett

    Hi, 

    Sorry, here's some more full models:

    The spectre.scs

    simulator lang=spectre

    subckt Parameter_test (N1 N2)

    parameters a=100
             + b=a*10

    test_R (N1 N2) resistor r=b

    ends Parameter_tes

    The input.scs:

    simulator lang=spectre
    global 0
    parameters temperature=27

    I0 (0 net1) Parameter_test a=100 b=a*10
    I3 (0 net1) isource type=pulse val0=0 val1=1A period=10n delay=0 rise=1p \
            fall=1p width=1n
    simulatorOptions options psfversion="1.4.0" reltol=1e-3 vabstol=1e-6 \
        iabstol=1e-12 temp=27 tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 \
        maxnotes=5 maxwarns=5 digits=5 cols=80 pivrel=1e-3 \
        sensfile="../psf/sens.output" checklimitdest=psf 
    tran tran stop=100n write="spectre.ic" writefinal="spectre.fc" \
        annotate=status maxiters=5 
    finalTimeOP info what=oppoint where=rawfile
    modelParameter info what=models where=rawfile
    element info what=inst where=rawfile
    outputParameter info what=output where=rawfile
    designParamVals info what=parameters where=rawfile
    primitives info what=primitives where=rawfile
    subckts info what=subckts where=rawfile
    saveOptions options save=allpub
    include "...spectre.scs"

    Which results in error:

    ERROR (SFE-1997): "input.scs" 14: Cannot run the simulation because I0: parameter `b': Unknown parameter `a' has been specified in expression `a*10', correct the expression and rerun the simulation.

    And in the CDF (base):

    Thanks for your help. 

  • Andrew Beckett
    in reply to GT20260122746

    In the CDF, change the default value of b to either be blank (in which case it will use the default in the model if not specified), or to:

    iPar("a")*10

    which will ensure that it netlists the instance line correctly. Currently it is outputting b=a*10 on the instance line, and a in that context is the global a.

    Andrew

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