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Currents are not steady in AMS simulator ... why? (Read 2795 times)

pbennett

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Phoenix, AZ

Currents are not steady in AMS simulator ... why?
Sep 20^th, 2013, 8:07am

I have found that when I plot or measure currents in the AMS simulator that they do not appear to be steady. Why is this?

I have simulated several different designs ... mostly simple current mirrors and several other circuit blocks and I do not find that the current in AMS/spectre to be solid number like 10 uA ... instead it will numerically oscillate between 9.9 and 10.1ua in a very unpredictable and unsteady way ...

Do I have some accuracy setting wrong ?? Have others seen this behavior before?

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pbennett New Member Offline Posts: 3 Phoenix, AZ	Re: Currents are not steady in AMS simulator ... why? Reply #1 - Sep 20^th, 2013, 10:39am well it seems that just by tightening RELTOLfrom 1e-3 to 1e-5 ... makes a world of difference. I would still be interested if anyone has any additional guidance regarding this issue. The simulator of course runs much slower but at least the answers seem to be correct!
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Ken Kundert Global Moderator Offline Posts: 2386 Silicon Valley	Re: Currents are not steady in AMS simulator ... why? Reply #2 - Sep 20^th, 2013, 3:24pm Sounds like trapezoidal-rule ringing. Is it a point-to-point ringing? If so, switch the transient integration method to gear2. -Ken
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pbennett New Member Offline Posts: 3 Phoenix, AZ	Re: Currents are not steady in AMS simulator ... why? Reply #3 - Sep 20^th, 2013, 4:50pm Yes it seems to be point to point ringing. I will try your suggestion to move to gear2 method. TNKS
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