Stats

  • Locked Locked
  • Replies 3
  • Subscribers 64
  • Views 10801
  • Members are here 0
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

AMS transient simulation does not run beyond 7000s

RFStuff

Dear All,

I am running a testbench with sampling frequency of 1s (in other words my clock period is 1s).

Aim is to run the transient simulation beyond 10000s so that I can capture atleast 10000 samples for my post analysis of the circuit.

Thsi transient simulation run well beyond 10000s if I run it Spectre. But, if I run it in AMS, it says "Unable to run simulation because the specified transient analysis stop time exceeds the maximum of 9000 seconds. Modify the stop time to a value less than or equal to 9000 seconds and run simulation again. xmsim: *F,ALGFLT: Simulation terminated due to error from analog solver."

I then set transient run time of 9000s. Now, AMS simulation ran but it stopped at 7000s. I wonder why it is happening like this any way it is using the specter engine.

May I know why this is happening in AMS and how can we get over this issue ?

Kind Regards,

  • This is, I believe, a limitation of the digital engine. Spectre uses floating point time and so you can have very long stop times - you just lose the ability to have sharp transitions because it's stored as a double-precision floating point number (which means you have about 14-15 digits of resolution).

    XCELIUM/INCISIVE use 64-bit integer for time with 1fS resolution, which means that your maximum time is 2^63*1e-15 which is 9223.37s - I think there's an error check somewhere in the code to constrain it with AMS to 9000s which is a little under the 9223s maximum. Even with a pure digital simulation I can't run beyond 9223s.

    I did some quick searches but didn't see whether there's a way around it. There is this article which talks about the maximum time.

  • in reply to Andrew Beckett

    Thanks Andrew.

    Is it possibe then, to ensure a transient simulation to be evaluated at particular time instants  in Spectre. For example at multiple 1s in the above case.

    I was thinkig strobeperiod would ensure this.I simply added a sine wave voltage source of 0 phase and 1Hz frequency and simulated with the strobeperiod=1s. I plotted the voltage source output. It should be zero. But, it is NOT coming in the plot (it wggles to amximum 1.7 uV).

    cross() function in veriolg-A also seems to be not helpful in this regard as it has a time-tolerance and mplitude tolerance.

  • in reply to RFStuff

    I don't really understand how that would help solve a limited maximum time on the digital engine. All strobeperiod does is force a tilmestep close to the desired regular period, but the simulator will still take whatever time steps it needs to follow the waveform. You'll still see some variability in the values if strobing at the exact crossing point - but this is just small error within the tolerances (at least it should be) - for me the biggest value was something like 140nV, but of the order of a uV is reasonable if you have a couple of volts (vabstol would be 1uV by default). As I said though, I can't see how this is related in any way to hitting a maximum time in the digital engine...

    Andrew

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.