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Tip of the Week: stb or ac simulation around a transient op point

archive

Normally, stb or ac simulation proceeds at a DC operating point that is calculated at the start of the sim. But there are times when it can be useful to have the stb or ac analysis performed at some other operating point.  One example might be the far extreme transient output voltage swing of an amplifier, where the gain can be quite degraded compared to its midpoint. This email tells how to set that up.

1. Configure the simulator to run both a stb (or ac) and a transient simulation.

2. Configure the transient simulation to end at the point in time at which you wish the ac analysis to be performed.  (For example, at a time when you know the amplifier's output will be at full-scale.)

3. In the simulation window, go to Analysis-->Choose-->stb (or ac)-->options, and set "prevoppoint" to "yes". This tells the simulator to use the final value of the transient simulation as the operating point for the stb or ac simulation.

4. Run the simulation. The transient will run first, then the stb or ac will run using the final value from the transient as the operating point.

- Hugh


Originally posted in cdnusers.org by Hugh
  • archive

    i tried this useful thing but was not able to find prevpoint .. However i found oppoint but that was not useful!


    Originally posted in cdnusers.org by dozy_walia
  • archive

    What version of the tools are you running?  In version 5.1, the "prevoppoint" button is at the very top of the "options" form for both the stb and the ac analyses (in the "State-file parameters" section).

    - Hugh


    Originally posted in cdnusers.org by Hugh
  • jugemu1234

    Hi

    My icfb ver is like this,

    icfb.exe version 5.1.0 03/01/2009

    Even following your instruction, tran does NOT run first. Stb analysis runs first all the time. I posted different forums as well but I really like to run stb analysis around the op derived from transient. Pls help me out asap.

    Thanks.

  • Andrew Beckett

    Doesn't make an enormous amount of sense replying to a post which is over 2 years old; it's better practice to start a new one referring to the old one (I think), but anyway...

    Try using the Setup->Environment form, and looking at the "Analysis Order". You can enter "tran stb" in this field to tell it what order to do the analyses in, which will override the default (I can't remember the default).

    The other thing you could do is use the "acnames" and "actimes" parameter of the tran analysis to tell it the name (stb) and the time you want to do the stb analysis at during the transient.

    Regards,

    Andrew.

  • MarkSummers

    The solution below shows how you can do this multiple times with AC or STB analysis inside a transient run.  This way you can check things at multiple time points.  See documentation for full details.

     

    Can Spectre run multiple ac analysis during a single transient?

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    Error Message
    None
    Problem

    You want to be able to run multiple ac analysis at multiple timesteps during a transient analysis, without halting the analysis. Hspice has this capability but you do not seem to be able to perform the same type of operation. Spectre seems to allow you to only run multiple info statements during a transient using infotimes/infonames. How can you perform the same operation for ac analysis in Spectre?

    Solution

    Enhancement PCR 767092 was filed to provide this capability and the solution has been released in MMSIM60USR2 and above. Starting in MMSIM60USR2, you can compute an ac analysis at multiple timesteps during a transient without stopping the simulation.

    You will use for this acnames and actimes parameters.

    The syntax for performing a small-signal analysis during transient analysis is:

     

    Name tran stop=stop actimes=time acnames=name

     

    where

     

    Name: The name of the transient analysis

    stop: The time at which the transient analysis is to be put on hold..

    actimes :The time points at which the analyses specified by the acnames parameter are

    performed.

    acnames:The names of the analyses to be performed at each time point specified by the infotimes parameter. The analyses you can can specify here are info, ac, noise,

    xf, and sp.

     

    For example:

       tran1 tran stop=10u acnames=[myac] actimes=[1u 2u ]

       myac ac start=1 stop=100e9 dec=100

    In this example, the ac analysis myac will be run at respectively 1u and 2u during the transient analysis.

     

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