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Simulators >> RF Simulators >> Zero Diagonal Found in Jacobian!
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Message started by schehrazi on Nov 26^th, 2006, 10:06am

Title: Zero Diagonal Found in Jacobian!
Post by schehrazi on Nov 26^th, 2006, 10:06am

Hi,

When does Spectre prompt the following convergence issue?

Zero diagonal found in Jacobian at 'nodeX' and 'nodeX'

Does a certain circuit condition lead to this error? I should say that I am trying to simulate a mixer with VerilogA square law transistors using PSS. I am My VerilogA model covers both saturation and triode operation regions.

Thank you so much.

Title: Re: Zero Diagonal Found in Jacobian!
Post by Geoffrey_Coram on Nov 27^th, 2006, 5:16am

You've probably got a poorly-defined model. What happens in subthreshold? If you don't have a GMIN or subthreshold current equation, then you'd likely get a zero diagonal message. The Jacobian (matrix) is loaded with partial derivatives of all the currents with respect to the node voltages. If there's a zero diagonal at nodeX, then it means that, when linearized about the operating point, changing the voltage on nodeX will not affect the current into nodeX.

Title: Re: Zero Diagonal Found in Jacobian!
Post by schehrazi on Dec 12^th, 2006, 11:12am

Thanks, I fixed it by changing the initial condition parameters of PSS.