What happens after PSpice>Run?

After pressing PSPpice>Run in Capture:

A netlist gets created

The simulator searches the configured libraries for Models required by the netlist

A check is made for any errors

The simulation starts: a Bias Point is found (may be skipped for a Transient Simulation); the secondary simulation (if any) is run; results are displayed in the Probe Window and / or written to the Output File.

Finding a Solution

To find a solution: currents must sum to 0; Gaussian Elimination is used to solve linear elements; Newton-Raphson, successive approximation, is used to solve non-linear elements.

A solution is found when successive passes of the simulation are within the specified Tolerances. The Tolerances are: RELTOL, relative accuracy of Voltages and Currents, default value 0.1% of magnitude; VNTOL, Absolute accuracy of Voltages, default 1uV; ABSTOL, Absolute accuracy of Currents, default 1pA.

So, the Voltage nodes reach a solution, converge, when a Voltage is within ((Voltage node magnitude * RELTOL) +/- VNTOL) on successive passes. The Current branches converge when a Current is within ((Current branch magnitude * RELTOL) +/- ABSTOL)

How many passes the simulator makes is controlled by the Iteration Limits (ITL). In the Simulation Options: ITL1 is used for DC Bias calculations and the default value is 100; ITL2 is used for DC Sweep and the default value is 40; ITL4 is used for Transient Analysis and the default is 10.

The absolute limits of the simulator are: Voltage and Current magnitude: 1e10, and the dynamic range is about 1e12.

If finding a solution, convergence, is an issue, the number of iterations can be increased, the accuracy can be reduced. AutoConvergence is provided to increase all of the iteration limits and reduce the accuracy, once the simulation converges, the iteration limits can be reduced and the accuracy increased, if required.

Use of NODESET – “hints” the Bias calculation – and IC (Initial Condition) – forces a node, or branch, at the start of a Transient simulation – can also help the simulator to find a solution.

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