ratazzie@lonex.radc.af.mil (Edward P. Ratazzi) (03/12/91)
I came across the following messages while attempting a simulation using SPICE3C1 on our Sun 3/470. Note that the same simulation runs fine using SPICE2G6. My question is: does anybody have any idea why this is happening, and what would be a typical fix for this type of problem (i.e. do I tweak certain analysis options?)? SPICE3 3 -> run Warning: resuming run in progress. Warning: Gmin step failed Warning: Gmin stepping failed Warning: source stepping failed doAnalyses: Improperly formed matrix - shouldn't happen!(preOrd) simulation interrupted SPICE3 4 -> Many thanks. -- E. Paul Ratazzi | ratazzie@lonex.radc.af.mil Microelectronics Reliability Division | COMPMAIL: e.ratazzi Rome Laboratory | (315) 330-2946 "Exploring the Invisible Frontier" | DSN 587-2946
ins_atge@jhunix.HCF.JHU.EDU (Thomas G Edwards) (03/14/91)
In article <1991Mar11.215449.8066@lonex.radc.af.mil> ratazzie@lonex.radc.af.mil (Edward P. Ratazzi) writes: >SPICE3 3 -> run >Warning: resuming run in progress. >Warning: Gmin step failed >Warning: Gmin stepping failed >Warning: source stepping failed >doAnalyses: Improperly formed matrix - shouldn't happen!(preOrd) The first thing I would do is check your circuit to make sure you aren't doing anything silly. Since the circuit worked on the other SPICE version, I guess it passes this test. GMIN is the minimum conductance of any branch. This conductance is in parallel with every branch (thus also parallel with transistor junctions). I believe if there is a problem with convergence, the effective GMIN is stepped up to the max value set in the .OPTION statement. I encounter this area typically when the Vgs of my transistors is very close to zero (less than 0.1V). Here's a list of ways to avoid the GMIN stepping syndrome: 1) use .IC to set initial conditions on gate voltages so the Vgs of every transistor is at least 0.2V when the simulation begins ...or... If you are doing a .DC analysis, ensure that your voltage source doesn't bring the Vgs of any transistor below 0.2V ...if this doesn't work... 2) increase RELTOL (the relative accuracy of V's and I's) up to 0.005 using a .OPTION statement. Then try 0.01, 0.02, etc. Try combinations of ABSTOL larger than 1pA, and CHGTOL larger than .01pC. You will find, however, that if you adjust RELTOL much larger than 0.01 that transient analyses will begin to behave a little on the chaotic side. ...if you are at the end of your rope... 3) Increase the GMIN in the .OTION statement up from 1E-12 Ohm^-1. Notice that when you significantly increase your GMIN, a lot of current can leak to places you never expected it (gee...why is my oscillator going that fast!). Good luck! -Thomas Edwards