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Simulation results is different for the same circuits when "No connections to node `0'" between MMSIM13 and MMSIM15

lightcoming

All the simulator options is same between MMSIM13 and MMSIM15, for gmin=1e-14, the output ac response is different when the gnd is not connected.

why?

 

Parents
  • Andrew Beckett

    Why are you trying to simulate without the ground connected? In both cases you're probably getting numerical noise (unless I've misunderstood your question, which isn't surprising given the sparsity of information in your post). Seeing the circuit and the simulator output log might help here...

    Andrew.

  • lightcoming
    in reply to Andrew Beckett

    Hi, Andrew. Thanks you for your reply. The reason why I simulated the circuits without the ground connected is that I find the simulation results is different when I simulated the comparator input noise in different spectre version. So I take a easy filter circuits without the ground connected to observe the noise level. Here are some details about the comparator input noise simulation. The first figure is the schematic of comparator, and the second is the tran analyses setting. The last is probability of comparator output voltage large than 0.5 in different input voltage.  So I suspect whether the mechanism of the noise generation is different in different spectre version.

    schematictran analyses setting the probability of comparator output large than 0.5 in different input voltage

Reply
  • lightcoming
    in reply to Andrew Beckett

    Hi, Andrew. Thanks you for your reply. The reason why I simulated the circuits without the ground connected is that I find the simulation results is different when I simulated the comparator input noise in different spectre version. So I take a easy filter circuits without the ground connected to observe the noise level. Here are some details about the comparator input noise simulation. The first figure is the schematic of comparator, and the second is the tran analyses setting. The last is probability of comparator output voltage large than 0.5 in different input voltage.  So I suspect whether the mechanism of the noise generation is different in different spectre version.

    schematictran analyses setting the probability of comparator output large than 0.5 in different input voltage

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  • Andrew Beckett
    in reply to lightcoming

    I don't understand how simulating without the ground connected is useful - circuit simulators need a ground node as a reference.

    There's not really enough information to go on here to explain the difference. It might be that the default noisefmin changed to 1Hz (I can't remember exactly when that happened). The best thing here would be to contact customer support as then you can hopefully provide the input.scs and simulator log files (I asked for the simulator logs earlier). Your picture above isn't really enough as it doesn't explain how it's connected up, and even then I doubt I'd be able to get to the bottom of it without seeing more information.

    Regards,

    Andrew.

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