First you have to understand what type of convergence problem you are getting. The most common type is "DC convergence" . Generally, howeve the more troublesome type is Transient convergence problems. To get a handle on these problems it is best to run the simulator stand alone in a command line window on the circuit file. In Specctraquest the simulator is "tlsim"and the top level spice file is "main.spc". Many of the following observations are common to most circuit simulators 1. DC convergence: 1.1 The most common type occurs in large circuits ( 1000's of nodes, circuit file containing huge passive package and connector models). Contrary to what the simulator says, in most cases this is not a convergence problem at all but actually result of numerical error caused by huge ill conditioned dc matrix. The classic brute way to force a solution here is to install a small conductance to ground at every node. In tlsim you can do that by using the command line option MinNodeToGndCond 1.2 Another popular source is inconsistent tv curves or leaky clamp curves in IBIS models. For example if you have a leaky clamp (i.e clamp draining a small current at the dc operating points) and your circuit is unterminated, you certainly will have a convergence problem because conservation is violated! If the leak is "small" the MinNodeToGndCond will solve it. If your problems is due to tv curves, you can delete these curves from the local ibis_models.inc file. Alternatively you can globally turn of all the tv curves at once using a command line option (I believe) BhvrTvOff OR BhvrModelsTvOff 1.3 In rare instances there may be a "legitimate" convergence problem due to non-linearity in IBIS models. You can try command line options like BhvrDcModifyNewtonOff 2. Transient Convergence These are generally difficult to debug. But in many instances you can make educated guesses. 2.1 You can turn on variable time step in tlsim using VariableTstepOn This is slow in tlsim but usually will solve transient convergence problem. But the circuit may actually have a real problem and you may find the solution unsatisfactory. 2.2 By intelligent poking and guessing you can solve the problem by adding small shunt or floating capacitors. This "method" will work most of the time. (You can brute force this by adding a shunt capacitance (similar to shunt conductance), but this will not help you in debugging complex problems). While debugging, it is good to remember that tlsim automatically paritition's the transient circuit into many small circuits when it encounters a transmission line. 2.3 You can also try command line option BhvrTransientModifyNewtonOff Hope this helps. - kumar James_R_Jones@xxxxxxxx wrote: Gurus, I was interested in learning more about the convergence issues in SpecctraQuest. I get quite a few of these when I simulate, with severity ranging from "Serious Convergence Error", to "jagged" waveforms, to no convergence problem at all. Does anyone have a good understanding of what causes these convergence issues and how to prevent them? A couple of theories that I have heard so far include: 1. Spectral content resonating back and forth along transmission line segments that is aliased back as noise causing the "jagged' waveforms. 2. Simulator is confused, particularly during design link, by reference designators and makes 'mistakes' in handling topology. Has anyone done work in this area to determine the cause of these convergence issues? Any help is appreciated. Thanks in advance, James R. Jones ESG Signal Integrity Dell Computer Corporation (512) 725-1809 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu --------------------------------- Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu