解决pspice中遇到的convergence问题.doc

Solving SPICE Convergence Problems Key Sources The following techniques on solving convergence problems are taken from various sources including: [1] Meares, L.G., Hymowitz C.E. “SIMULATING WITH SPICE”, Intusoft, 1988 [2] Muller, K.H. ”A SPICE COOKBOOK”, Intusoft, 1990 [3] Meares, L.G., Hymowitz C.E. “SPICE APPLICATIONS HANDBOOK”, Intusoft, 1990 [4] Intusoft Newsletters, various dates from 1986 to present [5] The Designers Guide to SPIC and Spectre, Kenneth S. Kundert, Kluwer Academic Publishers, 1995 [6] The SPICE Book, Andrei Vladimirescu, John Wiley Sons Inc,, 1994 [7] Inside SPICE, Ron Kielkowski, McGraw-Hill, Inc. 1994 What is Convergence? (or in my case, Non-Convergence) The answer to a nonlinear problem, such as those in the SPICE DC and Transient analyses, is found via an iterative solution. Forexample, ISSPICE makes an initial guess at the circuit’s node voltages and then, using the circuit conductances, calculates the mesh currents. The currents are then used to recalculate the node voltages, and the cycle begins again. This continues 355 WHAT IS CONVERGENCE? until all of the node voltages settle to values which are within specific tolerance limits. These limits can be altered using various .Options parameters such as Reltol, Vntol, and Abstol. If the node voltages do not settle down within a certain number of iterations, the DC analysis will issue an error message such as “No convergence in DC analysis”, “Singular Matrix”, or “Gmin/Source Stepping Failed”. SPICE will then terminate the run because both the AC and transient analyses require an initial stable operating point in order to proceed. During the transient analysis, this iterative process is repeated for each individual time step. If the node voltages do not settle down, the time step is reduced and SPICE tries again to determine the node voltages. If the time step is reduced beyond a specific fraction of the total analysis time, the transient analysis will issue the error message, “Time ste