How to vary a schematic variable as a Gaussian distribution in Spectre?

Discussion in 'Cadence' started by Setu, Feb 27, 2007.

  1. Setu

    Setu Guest

    For performing a Monte Carlo (MC) analysis, I would like to vary a
    schematic variable according to a Gaussian
    statistical distribution and repeat a DC sweep analysis 100 times. How
    can this be done?

    Background for the request:
    In the current MC methodology in Cadence, one has to modify the model
    file in order to set up statistics blocks for individual parameters
    mentioned in the model file - this is very cumbersome. Especially in
    the case of complex Spectre models, it is difficult to go from foundry
    mismatch information, on say, Vt mismatch or resistance mismatch, to
    figuring out which model parameter should be varied in order to have a
    realistic MC simulation. Frankly, I don't even know what all the BSIM3
    model parameters mean!

    My design is an R-2R DAC. Mismatch in the different resistors in the
    ladder gives rise to non-linearity errors. To characterize the effect
    of resistor matching on yield, I want to define the value of my unit
    resistor as a design
    variable in ADE, say with mean of 1K and standard deviation of +/- 1%
    of nominal value. Then I want MC to vary the value of this resistor
    according to a Gaussian distribution with the above mean and standard
    deviation and repeat a DC analysis (input sweep) at each MC iteration
    and just give me those plots. This will tell me the information I
    want.

    How can this be accomplished simply without too much hacking in Ocean
    or the model file? I find the current MC methodology really difficult
    and obtuse to use. Other simulators like GoldenGate have the ability
    to define variables with distributions in ADE. Spectre should have
    this ability as well.

    Thanks,
    Setu
     
    Setu, Feb 27, 2007
    #1
  2. Setu

    JD Guest

    In oder to use MC, you must have statistical block in your model
    file.

    There is not way you can do random sample with sweep analysis.

    So modify you models to add mismatch parameters and add statistical
    block is the only way to do MC samples in Cadence.
     
    JD, Mar 9, 2007
    #2
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