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Cadence SKILL/Ocean loading and saving dc operating point in dc sweep simulation

MatthewT

Hi,

I looked into web and cadence manuals, but I cannot find the answer to my question. I think I saw it some time ago on our forum here, but I cannot find it right now.

I'm running dc simulation:

analysis('dc ?dev "/voltage_dc_source"  ?param "dc"  ?start "value_low" ?stop "value_high"  ?step "1m" )
envOption(
          'analysisOrder  list("dc")
); envOption
run()


I would like to have faster convergence. I found following commands:
- write
- writefinal
- readns

I can run .tran simulation with "?writefinal" attribute pointing to the file where .op of the circuit will be saved and then load it for dc simulation:

analysis('tran ?stop "500n" ?writefinal "tran.fc")
envOption(
    'analysisOrder  list("tran")
); envOption
run()

(...)

analysis('dc ?dev "/voltage_dc_source"  ?param "dc"  ?start "value_low" ?stop "value_high"  ?step "1m" ?readns "tran.fc" )
envOption(
    'analysisOrder  list("dc")
); envOption
run()    


however in such a case, every dc simulation uses the same input tran.fc file. The question is, is it possible to:
1. run 1st dc sweep
2. save calculated dc operating point
3. start 2nd sweep
4. load dc operating point from the 1st sweep
5. run 2nd sweep
6. save dc operating point of 2nd sweep
7. and so on ...

?

Parents

  • I don't think in general that restart is going to make much difference in this case. The operating conditions would always be changing here, and so it's always going to start from the previous initial guess.

    The difference you're seeing is purely down to the initial DC operating point - the ?readns is allowing it to compute the initial operating point based on the transient solution. After that, each point in the DC sweep is probably close to the previous one and hence it converges quickly. That's what I would have expected - so there's going to be no benefit of using a nodeset between points in the sweep (not that you can do it anyway).

    Regards,

    Andrew.

Reply

  • I don't think in general that restart is going to make much difference in this case. The operating conditions would always be changing here, and so it's always going to start from the previous initial guess.

    The difference you're seeing is purely down to the initial DC operating point - the ?readns is allowing it to compute the initial operating point based on the transient solution. After that, each point in the DC sweep is probably close to the previous one and hence it converges quickly. That's what I would have expected - so there's going to be no benefit of using a nodeset between points in the sweep (not that you can do it anyway).

    Regards,

    Andrew.

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