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Monte Carlo simulation with verilog-a model using Spectre

yueguoguo

Hi all,

I have written a behavioral model using verilog-a and want to simulate it using spectre.

Additionally, I want to study how the statistical variations of some of the parameters defined in my model affect the overal electrical characteristics, that is, I need to do a Monte Carlo simulation for this study.

I know how to do the Monte Carlo simulation provided with foundry PDK, so my problem is whether can I do the Monte Carlo with the parameters that I defined in my verilog-a model and plot the statistical analysis results as a histogram or something?

Thanks if any of you could lend me a hand on this!

-yueguoguo 

Parents

  • Hi Andrew,

    Thank you for the link to the solution. I've tried it myself and it works. However, I wonder if it's possible to define the statistical parameter with respect to another parameter of the model.

    Say I have modeled a current source (see below) and I want the standard deviation to be a certain percentage of the value that the user defines in the schematic for the specific model. 

    --

    // VerilogA for user, vccs_mc, veriloga

    `include "constants.vams"
    `include "disciplines.vams"

    module vccs_mc(vpos,vneg,ipos,ineg);

    inout vpos,vneg,ipos,ineg;
    electrical vpos,vneg,ipos,ineg;

    (*cds_inherited_parameter*) parameter real gm_mc = 0;

    parameter real gm = 1u;
    localparam real gm_effective = (1+gm_mc)*gm; // nominal transconductance plus monte-carlo mismatch effect

    analog begin
    I(ipos,ineg) <+ gm_effective*V(vpos,vneg);
    end

    endmodule

    //

    How shall I define the variation of the parameter gm_mc in the .scs file such that is taken into account properly ? Currently I have the following:

    parameters gm_mc = 0

    statistics{

    mismatch {

    vary gm_mc dist=gauss std=1 percent=yes

    }

    }

    But when I run the Monte Carlo the simulator complains there's no statistical variation.

    Thanks in advance.

    Lucho

Reply

  • Hi Andrew,

    Thank you for the link to the solution. I've tried it myself and it works. However, I wonder if it's possible to define the statistical parameter with respect to another parameter of the model.

    Say I have modeled a current source (see below) and I want the standard deviation to be a certain percentage of the value that the user defines in the schematic for the specific model. 

    --

    // VerilogA for user, vccs_mc, veriloga

    `include "constants.vams"
    `include "disciplines.vams"

    module vccs_mc(vpos,vneg,ipos,ineg);

    inout vpos,vneg,ipos,ineg;
    electrical vpos,vneg,ipos,ineg;

    (*cds_inherited_parameter*) parameter real gm_mc = 0;

    parameter real gm = 1u;
    localparam real gm_effective = (1+gm_mc)*gm; // nominal transconductance plus monte-carlo mismatch effect

    analog begin
    I(ipos,ineg) <+ gm_effective*V(vpos,vneg);
    end

    endmodule

    //

    How shall I define the variation of the parameter gm_mc in the .scs file such that is taken into account properly ? Currently I have the following:

    parameters gm_mc = 0

    statistics{

    mismatch {

    vary gm_mc dist=gauss std=1 percent=yes

    }

    }

    But when I run the Monte Carlo the simulator complains there's no statistical variation.

    Thanks in advance.

    Lucho

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