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Transient simulation - adding noise after steady state

jehh

Hi,

We have a fairly large mixed-signal block, where we would like to get some transient simulation data with noise. However, to save simulation time, we would like to run up to steady-state first, without noise, and then add noise and simulate for some more time.

I did run a transient simulation with a save snapshot after steady state - however when I try to restart, it fails with a SimError (and seemingly nothing in the logs?) - I probably messed something up, allthough I am not entirely sure on what. I have two questions:

A) Is this snapshot saved somewhere, so I can try and save it for future use?
B) Is this method at all possible? Before I try and redo the transient steady state simulation (7 days of sim time) I would like to know if this is the most effiecient approach?

BR,
Christian

Virtuoso IC6.1.8-64b.500.20
Spectre 20.1.0.298.isr9
Xrun 20.09-s008

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  • Andrew Beckett
    jehh said:
    We have a fairly large mixed-signal block, where we would like to get some transient simulation data with noise. However, to save simulation time, we would like to run up to steady-state first, without noise, and then add noise and simulate for some more time.

    Hi Christian,

    This can be done simply by using the dynamic parameters capability on the transient form. Turn on transient noise as normal, and then in the dynamic parameters section choose the parameter isnoisy. Set it to "no" at time zero, and to "yes" at some suitable time after it has reached steady state. Note that if you have some way of detecting that the circuit is in steady state, it is possible to enable this based on an event in the circuit - but let's cross that bridge once you've got the basic idea working (there would need to be either a Verilog-A model detecting the event or a a spectre assert to detect the event if you want to use this approach).

    Unlike Shawn's concern, this is likely to help with performance as the noiseless transient will run faster, and introduction of the noise sources are unlikely to create a significant enough disturbance to cause a convergence difficulty at the time they are applied (it's no worse than the random variation that will happen at each time step after that).

    Regards,

    Andrew

Reply
  • Andrew Beckett
    jehh said:
    We have a fairly large mixed-signal block, where we would like to get some transient simulation data with noise. However, to save simulation time, we would like to run up to steady-state first, without noise, and then add noise and simulate for some more time.

    Hi Christian,

    This can be done simply by using the dynamic parameters capability on the transient form. Turn on transient noise as normal, and then in the dynamic parameters section choose the parameter isnoisy. Set it to "no" at time zero, and to "yes" at some suitable time after it has reached steady state. Note that if you have some way of detecting that the circuit is in steady state, it is possible to enable this based on an event in the circuit - but let's cross that bridge once you've got the basic idea working (there would need to be either a Verilog-A model detecting the event or a a spectre assert to detect the event if you want to use this approach).

    Unlike Shawn's concern, this is likely to help with performance as the noiseless transient will run faster, and introduction of the noise sources are unlikely to create a significant enough disturbance to cause a convergence difficulty at the time they are applied (it's no worse than the random variation that will happen at each time step after that).

    Regards,

    Andrew

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