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MC in cadence

RAO VINAY

Hi all,

I am new to monte carlo analysis features and I am unable to interpret results from that simulation in cadence. I have designed band-gap current reference and I want to know how the resultant current varies with process and mismatch. I have a set-up and had few runs. For some runs, it generates Gaussian distribution but for some other runs it generates only a single bin in histogram where all the samples are in one particular range. I am having few following doubts about MC analysis.

1> How do we go about MC analysis? Whether we have to start from some definite seed, where we have to do some trial and error and find out which seed gives the best? I think in my case, it may be generating all those samples which are very close, so all the samples' response is concentrated in one point.

2> What is child analysis? Whether every general analysis such as DC, AC, Tran, SP etc. are called child analysis?

3> How samples are taken when I have a selected child analysis. Ex: When I am varying temperature from -10 to 100 Deg C, each other samples are considered at which temperature? It is important because response is a scalar quantity and don't know those responses are w.r.t which temperature value.

4>How to plot or record responses for AC, Tran, SP etc for different samples ? Ex: I want my resulted current to be plotted w.r.t temperature along the x-axis but for different MC samples.

Thanks and regards,

Vinay Rao.

Parents

  • Hello Andrew,

    Thanks for your reply. For university, Rapid Action Kits are not accessible.

    I am using IC614.500.12 with ADEXL. I went through cadence documents but many points are not cleared enough. Sorry for flooding my doubts here.

    Coming to the above questions, can you elaborate more as I have got few doubts.

    2&3> a> Whether 100 runs mean 100 different statistical sweeps?

     b> If I select both process & mismatch, whether my statistical variables are mobility (u0) and threshold voltage (Vth) of each device?

    c> Each sweep consists of one child analysis (ex:I have selected DC sweep variable as temperature range under DC analysis). And each child analysis consists of one more sub-sweep (ex: temperature ranges from -10 to 100 Deg C). The final scalar outcome/result of single sample, which will be categorized under bins in histogram, corresponds to which combination of input conditions (ex: In the considered case whether outcome is due to statistical variable value+temp@27 or statistical variable value+ temp@-10 or statistical variable value+temp@100 Deg C)?

    3>It made me to think about basics again. If I am not misunderstood, isn't that by-default every corner is run at nominal temperature at 27 Deg C? In every literature, people have checked the response of every corner for wide range of temperature sweeps.

    4>In DC analysis, I have selected temperature sweep from -10 to 100 Deg C. My output expression for MC analysis is i(“M0/D” ?result “dc-dc”). I didn't select any corner for MC analysis instead everything ran for nominal with the model file being selected as MC (process & mismatch option also selected). I could plot the response but there is no difference between responses of different samples. Every curve is same for different samples. Is there any mistake in set-up?

    About results: Earlier I have selected only MC and later I have selected MC, ff, ss, snfp, fnsp. I am not finding attachment option for this reply to attach my output response.

    Thanks and regards,

    Vinay Rao.

Reply

  • Hello Andrew,

    Thanks for your reply. For university, Rapid Action Kits are not accessible.

    I am using IC614.500.12 with ADEXL. I went through cadence documents but many points are not cleared enough. Sorry for flooding my doubts here.

    Coming to the above questions, can you elaborate more as I have got few doubts.

    2&3> a> Whether 100 runs mean 100 different statistical sweeps?

     b> If I select both process & mismatch, whether my statistical variables are mobility (u0) and threshold voltage (Vth) of each device?

    c> Each sweep consists of one child analysis (ex:I have selected DC sweep variable as temperature range under DC analysis). And each child analysis consists of one more sub-sweep (ex: temperature ranges from -10 to 100 Deg C). The final scalar outcome/result of single sample, which will be categorized under bins in histogram, corresponds to which combination of input conditions (ex: In the considered case whether outcome is due to statistical variable value+temp@27 or statistical variable value+ temp@-10 or statistical variable value+temp@100 Deg C)?

    3>It made me to think about basics again. If I am not misunderstood, isn't that by-default every corner is run at nominal temperature at 27 Deg C? In every literature, people have checked the response of every corner for wide range of temperature sweeps.

    4>In DC analysis, I have selected temperature sweep from -10 to 100 Deg C. My output expression for MC analysis is i(“M0/D” ?result “dc-dc”). I didn't select any corner for MC analysis instead everything ran for nominal with the model file being selected as MC (process & mismatch option also selected). I could plot the response but there is no difference between responses of different samples. Every curve is same for different samples. Is there any mistake in set-up?

    About results: Earlier I have selected only MC and later I have selected MC, ff, ss, snfp, fnsp. I am not finding attachment option for this reply to attach my output response.

    Thanks and regards,

    Vinay Rao.

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