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https://designers-guide.org/forum/YaBB.pl Simulators >> Circuit Simulators >> spectre error in transient analysis of counter example https://designers-guide.org/forum/YaBB.pl?num=1519037370 Message started by abhilash_172 on Feb 19th, 2018, 2:49am |
Title: spectre error in transient analysis of counter example Post by abhilash_172 on Feb 19th, 2018, 2:49am Hi i am trying to simulate a counter using D flip flops. outputs are coming perfectly upto some time and then simulation log has warning " zero diagonal found in jacobian" .i am using MMSIM 151. i attached the screenshot. Regards abhilash. |
Title: Re: spectre error in transient analysis of counter example Post by abhilash_172 on Feb 19th, 2018, 2:50am virtuoso output log file |
Title: Re: spectre error in transient analysis of counter example Post by Geoffrey_Coram on Feb 22nd, 2018, 8:34am Did you write the code for the D flip flops? (Or where did you get them?) Do they properly handle mid-rail inputs? If the input is rising, and the simulator happens to pick a timepoint right when the input hits (vdd+vss)/2, do you end up with both the P and N devices off, so that there is no conductance on the output node? |
Title: Re: spectre error in transient analysis of counter example Post by Ken Kundert on Feb 23rd, 2018, 7:08pm A zero diagonal is unusual but it is not an error. The message is printed in the hopes that it might give a clue as to what is happening if something does go wrong, but it in itself is not an indication that anything has gone wrong. -Ken |
Title: Re: spectre error in transient analysis of counter example Post by abhilash_172 on Feb 25th, 2018, 2:01am Hi @ Geoffrey_Coram, i am simulating a D flop using transistors not the verilog code. 1 . in the waveform picture i posted output is coming for sometime, then there is solution error. 2 . tried increasing the cmin value in spectre options, Now its working fine, but if i run it for really long time again the same issue " zero diagonal found in jacobian". |
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