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APS simulation: When a DC supply isn't DC

BrJaWr

I'm getting strange behavior from an APS run and I'm hoping I can get some suggestions to debug/resolve the issue.  Basically, my waveforms are skipping around.  The problems started when I added a full extractions of one of the child blocks (other blocks were already post-layout).  The most egregious failure I've seen is the VDD supply.  For a single time step around 50ps into the simulation it drops down to 0 and then bounces right back.  This is a DC supply.  I'm seeing similar behavior on other pulse supplies where the voltage isn't following a straight line from start to finish.

I would suspect there was some convergence issue but the log file doesn't have any errors/warning during the run.  I've tried adding source resistance to the supplies which in the past has helped with convergence but it made no difference.

Any thoughts on how to debug this?  Options to try?  Ideas why a DC supply isn't DC?

Thanks in advance....

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  • Andrew Beckett

    Assuming by "DC supply" you mean it's directly connected to a voltage source, then the only reason I can see this happening is if you've not got something connected - typically things like not connecting the grounds properly can cause this because some part of the circuit is floating.

    This is probably something best dealt with by customer support because it would be much easier to see it. I doubt very much whether it is a simulator convergence issue - more likely to be a connectivity problem.

    Andrew.

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  • Andrew Beckett

    Assuming by "DC supply" you mean it's directly connected to a voltage source, then the only reason I can see this happening is if you've not got something connected - typically things like not connecting the grounds properly can cause this because some part of the circuit is floating.

    This is probably something best dealt with by customer support because it would be much easier to see it. I doubt very much whether it is a simulator convergence issue - more likely to be a connectivity problem.

    Andrew.

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