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Running multiple AC sims during a transient analysis

CADcasualty

I was looking for a way to run a transient analysis and at various times along the way perform an stability analysis. I found a way to do this via e.g.:

analysis('tran ?stop "250n" ?actimes list("0" "250n") ?acnames list("stb") )
analysis('stb ?start "10" ?stop "100M" ?dec "10" ?probe "/stage1/amp/I1/vinj" )
run()

However at the times I want to pause the transient analysis to perform the stability analysis I actually want to perform multiple stability analyses. An example reason is that my circuit is a multi-stage switched capacitor amplifier and in one phase all of the stages are disconnected so I can easily do separate stability analyses for each stage without them interfering with each other.

The method outlined in the code above only lets me do one stability analysis per paused transient time. I know there is a way to save the full transient state at various points during the transient simulation. Is there a way later to retrieve that state and force the circuit to use it for multiple subsequent stability analyses?

  • Andrew Beckett

    You can define more than one stability analysis - the rest you'd need to define in an include file rather than through OCEAN (so you could use OCEAN to add another model file (say) containing the spectre statements for the additional stability analyses). For example:

    stb1 stb start=1 stop=1G dec=20 probe=IPRB0
    stb2 stb start=1 stop=10G dec=20 probe=IPRB1
    stb3 stb start=1 stop=100G dec=20 probe=I7.IPRB1

    (they don't have to have the same sweeps). Then you can do ?acnames list("stb" "stb1" "stb2" "stb3") to reference the one defined via an analysis() call in OCEAN plus the rest coming from the include file.

    Regards,

    Andrew.

  • CADcasualty
    in reply to Andrew Beckett

    Just back into the office and wanted to say thanks for your assistance again. I'll give this method a try a little later on. It isn't very intuitive to me - it would be nicer if there was a way to just capture the nodes at a given transient time point and use that for any number of subsequent AC (or whatever) analyses.

  • Andrew Beckett
    in reply to CADcasualty

    Whilst it might seem a good idea to capture (say) the operating point as a set of node voltages/branch currents at a point in time and save this to a file, it could be problematic restoring that later, since even if you used it as an initial condition, it would probably clash with the driven voltages into the circuit unless they magically knew the time at which the operating point was captured and so the driven sources would be at their correct phase for that point. That's not possible, and I suspect the flow would be even more complicated as a result.

    Of course, this (using actimes during a transient with several analyses) would be a whole lot easier if ADE let you define multiple analyses of the same type in the UI (a long-standing request, unfortunately not entirely trivial to implement because of lots of assumptions in various places that there's only one of each type).

    Regards,

    Andrew.

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