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Monte carlo simulation question

Holz

Hi everyone,

I have a 16 bits adder circuit, and for each adder, it has three input ports: a,b and carry_in. I want to do monte carlo simulation(sweep these three input values) to analyze how the delay distributes.

So, the value of the inputs of each adder should be either 0 or VDD, I have no idea how to do this since there are no swept values, and if I write "vary ***" in "process", it will not work.

 

Thanks for the help!

Regards,

Holz

  • Andrew Beckett

    Holz,

    You could create a spectre file like this:

    parameters VDD=3.3 \
  dist0=0 bit0=(dist0>0?VDD:0) \
  dist1=0 bit1=(dist1>0?VDD:0) \
  dist2=0 bit2=(dist2>0?VDD:0) \
  dist3=0 bit3=(dist3>0?VDD:0)

statistics {
    process {
	vary dist0 dist=unif N=1
	vary dist1 dist=unif N=1
	vary dist2 dist=unif N=1
	vary dist3 dist=unif N=1
    }
}

    Then you could reference the bit0/bit1 etc on your input sources:

    Vb0 (b0 0) vsource dc=bit0
Vb1 (b1 0) vsource dc=bit1
Vb2 (b2 0) vsource dc=bit2
Vb3 (b3 0) vsource dc=bit3

    Hope that helps? Given that you can't have discrete distributions, I've just created uniform distributions between +/-1 for each and then the ternary expression on each "bit" parameter translates that to VDD or 0 depending on whether the dist parameter is positive or not.

    Andrew 

  • Holz
    in reply to Andrew Beckett

    Thanks, Andrew, this really helps!

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