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How can I automate noise margin calculation ?

marten

Hi all,

is there a way to automatically calculate the noise-margin of a given cell? For a single calculation I solve this manually by calculation the derivative of the output, and then determine V_IL, V_IH, V_OL, V_OH using the plot window.

Since I want to do Monte Carlo analysis, it would be better to have this automated. So, any suggestions from the community ?

Cheers,

Marten

Parents

  • Hi Martin,


    I was faced with a similar calculation on a few occasions. What I resorted to was to an ocean script following a DC simulation. Specifically, within the script, I ran a DC transfer function of the circuit using relatively small input voltage increments (0.1 mV if I recall). Following its completion, I could determine the derivative of the transfer function and then the input voltage at the point of interest where the derivative matched -1.  I iterated on the output voltage to locate the value closest to the value corresponding to the input voltage of interest using a search. This provided the data for the noisemargin computations. The script ran over all corners to complete the picture. This may not be the most efficient method, but it worked for me.

    I will let you be the judge!

    Good luck!

    Shawn

Reply

  • Hi Martin,


    I was faced with a similar calculation on a few occasions. What I resorted to was to an ocean script following a DC simulation. Specifically, within the script, I ran a DC transfer function of the circuit using relatively small input voltage increments (0.1 mV if I recall). Following its completion, I could determine the derivative of the transfer function and then the input voltage at the point of interest where the derivative matched -1.  I iterated on the output voltage to locate the value closest to the value corresponding to the input voltage of interest using a search. This provided the data for the noisemargin computations. The script ran over all corners to complete the picture. This may not be the most efficient method, but it worked for me.

    I will let you be the judge!

    Good luck!

    Shawn

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