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Simulators >> Circuit Simulators >> Warning which cannot be explained.
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Message started by shuting84 on Jan 23^rd, 2006, 5:19pm

Title: Warning which cannot be explained.
Post by shuting84 on Jan 23^rd, 2006, 5:19pm

i am using IBM 0.13 um PDK and hspice

**warning** in element= 42:cwiredb defined in subckt nfet
capacitance = 0.00 <= 0 farad, please verify it.

Warning: Pd = 2.75e-07 is less than W.
Model: 42:nfet
W = 3.2e-07, L = 1.2e-07

I keep getting such warnings on the elements of my subcircuit when I run my simulations. I checked my circuit and verified that PD >W.

I am assuming cwiredb refers to capacitance between drain and body. the body of my nfet is connected to ground, and drain is the output. they are totally not connected together. i have no idea why capacitance would turn out to be 0.

i am suspecting that while the model is being formed, some errors are occuring, and the simulator is trying to create a model which is different from what I am trying to create.

Title: Re: Warning which cannot be explained.
Post by Geoffrey_Coram on Jan 25^th, 2006, 10:21am

Can you find the subckt definition? Don't post any proprietary model parameters here. Presumably, the subckt has parameters W,L,AD,PD, etc.;
are they passed directly to the actual MOS element inside the subckt? I'm guessing not, and maybe the equations are confused.

I once found this in a different foundry's subckt for well proximity:

.param xw='1.5e-8' wint='6e-9' weff='l+xw-2*wint'

Note that weff is computed from l instead of w.