Convergence

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Convergence

Both dc and transient solutions are obtained by an iterative process which is terminated when both of the following conditions hold:

1.The nonlinear branch currents converge to within a tolerance of 0.1% or 1 picoamp (1.0e-12 Amp), whichever is larger.

2.The node voltages converge to within a tolerance of 0.1% or 1 microvolt (1.0e-6Volt),whichever is larger.

Although the algorithm used in SPICE has been found to be very reliable, in some cases it fails to converge to a solution. When this failure occurs, the program terminates the job.

Failure to converge in dc analysis is usually due to an error in specifying circuit connections, element values, or model parameter values. Regenerative switching circuits or circuits with positive feedback probably will not converge in the dc analysis unless the OFF option is used for some of the devices in the feedback path, or the .NODESET control line is used to force the circuit to converge to the desired state.