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Simulators >> Circuit Simulators >> warning message of negative resistance
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Message started by hzfeiyun on Nov 10^th, 2008, 12:08am

Title: warning message of negative resistance
Post by hzfeiyun on Nov 10^th, 2008, 12:08am

In the SPICE log file, I found there are some warning messages "resistance is negative" when using a sub-circuit model of a poly resistor.
Does it affect the final results of whole block? And, is there any quick way to solve it ?
Thx.

Title: Re: warning message of negative resistance
Post by Geoffrey_Coram on Nov 10^th, 2008, 6:56am

I would complain to your foundry modeling department. It could mean your whole simulation is corrupted.

It could be that the subckt has components for contact/end resistors and a body resistor, and only the end resistors are negative; if the body resistor is large and the end resistors aren't very negative, it could be OK.

The quick way to fix it is to replace the subckt model with a basic linear resistor -- assuming the nonlinearity isn't very strong and/or the resistor isn't in a performance-critical circuit.

Another possibility would be to change the geometry of the resistor such that the nonlinearity is reduced -- ie, double the W and L. Unfortunately, you might end up with a resistance that is still wrong, maybe it's 1/100 of the nominal (unbiased) resistance, but because it's not negative, you don't get any warnings.