Transient Analysis Error Messages

When Nexxim transient analysis is unable to complete its analysis successfully, it displays an error message. This topic provides an analysis of some of the error messages.

Unable to satisfy convergence tolerances at t=time

Nexxim was unable to achieve the accuracy specified by the RELTOL, ABSTOL, and VNTOL options at time time. During transient analysis, a variant of Newton’s method is used to attempt to solve the nonlinear algebraic problem generated at each time point. Convergence is achieved only when both a delta check and a residue check are satisfied. (The delta check and residue check are explained in the Nexxim DC Analysis topic; see Nexxim DC Analysis Convergence Criteria.) Convergence problems may indicate that some model parameters specified in the netlist are inconsistent or are not correctly interpreted.

• Verify the values of device parameters that are set by device instance statements or MODEL statements in the netlist.

Unable to satisfy local error tolerances on voltage at time time, node nodename

Although Nexxim was able to achieve convergence at time time, the resulting solution did not satisfy the local error tolerance. This usually indicates that there is a discontinuity or instability in the solution that the transient analysis engine could not step over.

• The best remedy is to change the circuit so as to eliminate the problem behavior.
• A second possible remedy is to adjust the local error tolerance itself. The local error tolerance is looser than the convergence tolerances specified by RELTOL, ABSTOL and VNTOL by a factor of TRTOL. You can relax all transient tolerances by increasing TRTOL to 10 from its default of 7.

See Timestep Control for more information on TRTOL and the local error tolerance.