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ncsim with Ultrasim very slow for post layout simulation

dogrush

Hi,

I am using ams/ncsim with Ultrasim solver to simulate a mixed signal design.

For pre-layout of analog part, the simulation could be done within 10 mins.

But for post-layout of analog part, that is, to use the generated Calibre view instead of Schematic view, the simulation requires several hours to finish the total simulation.

I am wondering why the ams/ncsim simulator becomes so slowly for post-layout simulation?

Thanks.

Jerry

  • Jerry,

    This depends on how the extracted view has been partitioned - if it has ended up with everything solved in the same partition and it's analog or SPICE, that will definitely get quite a bit slower because you have a much bigger matrix to solve. It's really hard to give advice here without understanding how things are set up so I'd strongly suggest you to contact customer support.

    Regards,

    Andrew.

  • Hi Andrew,

    Yes. The scale of post-sim is larger than pre-layout. But it is not a little bit slower, actually it is much slower.

    In fact, for mixed simulation with post-layout of analog part, using UltraSim as solver is even slower than using Spectre solver.

    I noticed that it reason is somewhat related to the number of probed pins. That is, if the number of probed pins is larger, the simulation speed is significant slower when using UltraSim solver. I guess it maybe because the probed pins/ios will bring some negative effects for circuit partitioning when using UltraSim solver. If the number of circuit IOs or probed pins is smaller, the simulation will be much faster.

    For using Spectre, no circuit partitioning is performed, so the simulation speed will not be affected by the number of pins.

    Right?

    Thanks.

    Jianlei

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