The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> Bizzare Behavior from vpulse
https://designers-guide.org/forum/YaBB.pl?num=1172170711

Message started by gloopydew on Feb 22^nd, 2007, 10:58am

Title: Bizzare Behavior from vpulse
Post by gloopydew on Feb 22^nd, 2007, 10:58am

I have a simulation that uses the vpulse source from Cadence's analogLib as a 20 MHz clock. The simulation runs for some time and then the output of the vpulse source goes nuts. No current sources used in the simulation. What causes this to happen?

Title: Re: Bizzare Behavior from vpulse
Post by Andrew Beckett on Feb 22^nd, 2007, 11:30am

What simulator are you using? That's fairly important information...

Also, what version of the simulator are you using?

I can't think of any reason why spectre would do this, for example. spectre will put a breakpoint at each point in the pulse source.

Can you post the line in the netlist representing the pulse source? That may give some clues.

Regards,

Andrew.

Title: Re: Bizzare Behavior from vpulse
Post by gloopydew on Feb 22^nd, 2007, 12:36pm

Sorry, new here. I am using Spectre 5.1.41 to simulate. Line with pulse generator is as follows:

V4 (SYSCLK AVSS) vsource type=pulse val0=0.0 val1=VDD period=50n delay=12u \
rise=1n fall=1n width=25n

The simulation will be okay until somewhere between 60us and 120us when the output of the pulse generator goes whacko. I have never seen this before, and don't know what could cause it.

Title: Re: Bizzare Behavior from vpulse
Post by byang on Feb 22^nd, 2007, 2:05pm

All simulators try to put break points. Usually this kind of behavior suggests a bug in the simulator, likely in double-precision number comparison. I know for sure that academic simulators such as Spice3 has this kind of problem. Hard to imagine Spectre still has this kind of problem.

byang

Title: Re: Bizzare Behavior from vpulse
Post by Ken Kundert on Feb 22^nd, 2007, 2:41pm

I believe this could occur if Spectre believes that the output waveform is insignificantly small. That would only occur if your circuit is unstable and some voltage is shooting off to infinity. You can set the option diagnose=yes to get Spectre to report on this. If you do have a voltage that is very large (would probably have to be larger than 1kV with normal tolerances), then you should probably fix your circuit or models, or switch to using relref=alllocal.

-Ken