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How to dc sweep Vth

CorradoN

Hi All, 

I'm a graduate student and I'm new to virtuoso. I would like to simulate the variation of the threshold voltage of a transistor (I'm not interested in evaluating circuit's robustness to parameters variation and a Monte Carlo analysis can't be the solution to my problem).

I tried to sweep the parameter in the model provided by the foundry, but it consists of a subckt with a nested model. Something like this: 

simulator lang=spectre
subckt pmos (d g s b)
parameters ...
....

m1 d g s b pmosmod ...
....

model pmosmod bsim4 type=p ...
....
vth0 = ...

Launching the simulation, I get the following error: 

ERROR (SFE-1997): "input.scs" 26: dc: parameter `mod': Invalid model name `pmosmod' was given as value of parameter `mod'.

Can I specify (I don't know how) that I want to sweep the parameter of that model, even if none of the istances placed in the schematics recall it directly?

Thanks,
Corrado

  • Andrew Beckett

    Hi Corrado,

    Sorry for the belated reply.

    You have to refer to the model name using the hierarchical instance name. So if you have an instance M2 which is using "pmos", the hierarchical name would be M2.pmosmod - and you can use that as the mod parameter in a dc sweep.

    Note that if the models are not being passed instance-specific model parameters, then they will be shared across all the instances, so sweeping vth0 on M2.pmosmod will also alter M1.pmosmod, I2.M4.pmosmod and so on. It doesn't matter which hierarchical path you give if they're shared. If however the model parameters are passed in from the surrounding subckt, they will be unique (also in Monte Carlo mismatch mode parameterised subckt models are also unique per instance - that's how mismatch works).

    Regards,

    Andrew.

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