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Parametric Analysis: Inconsistent Result

jiahaoli2012

Hi,

I am running a parametric analysis in Cadence. What I basically do is that I sweep a set of Ws, say W1~W5 , each taking three different values which makes it 3^5 different combinations in total, through parametric analysis of ADE,  run a transient analysis and get the result. Then I pick one specific combination that I ran the sweep for, and this time I run a single transient analysis from ADE. The result that I get from this single run is completely different from what I get from the parametric analysis. It is not even among the results of parametric analysis!


Kind regards,

  • Dear JIiahao Li,

    In my experience with several technologies, this is a common event. The basic issue relates to how your PDK implements handling variables when computing device parameters. As a result, device parameters will differ when a numerical value is assigned as an MOS length (W) when compared to its device W is a variable. I have been able to resolve the difference in performance by contacting our PDK group and reviewing the issue with them. The PDK group updated the PDK to provide identical MOS parameter computations using a variable and numerical value for a specific MOS device physical parameter. I hope this helps you.

    Shawn

  • The symptoms that Shawn describes is normally apparent if you have a design variable on the component value and sweep that - the act of setting it to a design variable in the schematic often would lead to an error at that stage because a callback will fail.

    In such situations you can use the "parameters" capability of ADE XL to perform the sweep, as that causes the CDF callbacks to be triggered as the netlist is generated for each point in the sweep.

    However, a common cause of the symptoms you describe is having circuits with multiple stable operating points - as a result your circuit may have more than one solution and which one you get can depend on where you start from.

    Kind Regards,

    Andrew.

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