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Transient simulation - Explanation required

write2rammy

Hallo All,

        I have simulated a D-latch using OFET. When running a transient simulation it gave me the following warnings.

 "Matrix is singular (detected at `NQ')"

"Zero diagonal at net1 and net1"
            Then the simulation ended prematurely with convergence problem. Now I ran the simulation using a cmin of 1fF and then the zero diagonal warning disappeared and the circuit also converged. But the first warning is still there. I am giving a pulsed input to DIN but the output of the latch (Q and NQ) doesn't change. Is this error due to cmin or the first warning? I know that cmin is used at all floating nodes to avoid convergence problem. But does cmin affect the functionality of the circuit? I have attached the model(with parameters input file) and schematic. The inputs used are as follows.

DIN - pulse (-0.2 , -14 V); CLK - pulse (-0.2, -10.2V, freq = 100Hz) ,NCL- negated CLK

 

 

ofet.zip

  • I get this error in all my circuits. Can somebody tell me what does the follwoing messages mean?

    "Matrix is Singular" & "Zero diagonal at net1 and net1" 

  • It usually means you have nonisolated solutions. Put another way, you have floating parts of your circuit with an unsufficient number of equations - so the matrix has more unknowns than equations and so there is a singularity in the matrix.

    You only uploaded the model and not the netlist. Probably the best thing would be to report this to customer support (http://support.cadence.com ) together with the data to reproduce the problem, and then one of the team should be able to help get to the bottom of this.

    Regards,

    Andrew.

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