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Dynamic Variable

Hmjafari

Hi, 

I have a simulation in ADE assembler where I run a transient sim first and use the final condition of the transient sim (Writefinal -->spectre.fc) as an initial condition to pss sim (readic). 

In my tran sim I have a low pass filter that I need to disable for ~300ns (using a pwl source to control) and enable after, to make sure that the filter output voltage is settled to correct value. When I run PSS sim, the tstab sims will see the PWL source in the schematic and start the tstab sim after final transition of the pwl source. So if I set the tstab time to 200ns, the total pss sim will be 300ns+200ns = 500ns. 

Is there a way to change the variable that control the filter on/off between tran/pss sim? I tried using the dynamic parameter and set the filter pwl source to transition at 1ns in pss sim, but that doesn't seem to have an effect. The pss sim logs show that its reading my parameter new value but the tstab sim still runs for 500ns. 

Here is how I am setting the filter control signal in pss sim:

Is there another way to do this? 

I can also make a run plan in Assembler and have a separate sim for tran and pss, but then I have to write the full path of the spectre.fc for pss "readic" which get cumbersome over multiple corners. 

Thanks a lot,

Hamed

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  • Dear Hamed,

    I am very familiar with the issue you face in trying to control a piecewise linear source in a pss simulation given spectre's behavior. I have filed two cases in the past asking R&D to reconsider the current algorithm to override a user supplied  tstab in a pss simulation in the presence of a piecewise linear source whose breakpoints are outside of or coincident with a user supplied tstab. However, their R&D is insistent on maintaining the existing algorithm. The suggestion they provided me after much "back and forth" of the arguments for and against follows:

    "The current behavior is the behavior since the very beginning of SpectreRF.

    We cannot easily change this because it could cause backward compatibility issues.

    Here is a suggestion:

    Add sources in the schematic to set up the desired behavior. Add one source for each different thing you want to test. Then add switches from analogLib to the individual sources. Connect the output of all the switches to the desired point in the circuit.

    Set the sources that control the switches to variable names like DC, PWL_PSS, etc. Then set the variables in ADE to select the desired input." 

    This may work in your specific case. Further, R&D did add an Application/Troubleshoot note concerning this issue at URL:

    support.cadence.com/.../ArticleAttachmentPortal

    I hope this provides a little help or insight into your specific problem!

    Shawn 

  • in reply to ShawnLogan

    Thanks a lot Shawn. I end up using "Run Plan" + specific .FC file for each corner. 

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