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how to use the random function in schematic?

lukelukeamd

  Hi

  The following function abRandomNormal had been defined in ciw and it works. However, when give 

abRandomNormal() as a value to resistor in analogLib, in the simulation, it reports the following errors.

Error found by spectre during hierarchy flattening.
 ERROR (SFE-1997): "input.scs" 21: Cannot run the simulation because V0: parameter `dc': Function `abRandomNormal' is not defined. Update the netlist to define the function.
 , correct the expression and rerun the simulation.

How to use the pre-defined function as a variable to the analogLib devices?

Thanks

defMathConstants('abRandomNormal)
defun(abRandomNormal nil 
    let((max((-1 >> 1)) U V) 
	(U = (float(random(max)) / max)) 
	(V = (float(random(max)) / max)) 
	(sqrt((-2 * log(U))) * cos((2 * (abRandomNormal.PI) * V)))
    )
)
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  • Andrew Beckett

    You can't put SKILL functions in expressions on instances like this.

    What exactly are you trying to do? When do you want the random value to be chosen? Are you trying to do some kind of Monte Carlo analysis? A bit of background as to what the goal is will help in giving you a suitable alternative.

    Andrew

  • lukelukeamd
    in reply to Andrew Beckett

    Hi Andrew

    Thanks for your reply.

    I would like to generate a random value resistor in my simulation. So I would like to generate a number and used it in schematic for resistor value.

    Thanks

    Brian

  • ShawnLogan
    in reply to lukelukeamd

    Dear Brian.

    I assembled one possibility if I understand your need that you might consider. Basically, I've assembled a script that accepts an exported Explorer/Assembler corners comma-separated variable file. As an example, suppose your design variable assigned to the random resistor is called "r_random_ohms" and you want to create N random samples about the average value "r_random_average" with a range of "r_random_range".

    The script "random_resistor.sh" in the compressed directory:

    www.dropbox.com/.../random_resistor_value_090922.zip

    searches the corner file for the design variable name and appends N test columns where the value of design variable "r_random" takes on N random values from [r_random_average - 0.5*"r_random_range] to [r_random_average + 0.5*"r_random_range] . All other design variables and model files in the last corner of the corner file you supply to the script take on the same values as the last corner. I created a test bench to test the methodology and some documentation and the examples are in the note at URL:

    www.dropbox.com/.../random_resistor_value_sml_091122v1p0.pdf

    The compressed file contains a README file that provides much of this information, the script command to create a couple of the example corner files I used.

    I hope I understood your question and this is of some help to you Brian. Please feel free to ask me to clarify any of my instructions - or relate any issues you may experience!

    Shawn

  • lukelukeamd
    in reply to ShawnLogan

    Thanks Shawn. It is interesting.

  • ShawnLogan
    in reply to lukelukeamd

    Dear lukelukeamd,

    I am glad you found it interesting! I thought it might be worth including the ability to generate a Gaussian distribution in addition to a uniform distribution and added that capability. THe updated script directory and documentation has been updated. An example of the simulated distributions using the uniform and gaussian distribution options from page 14 of the note is shown below.

    www.dropbox.com/.../random_resistor_value_090922.zip

    www.dropbox.com/.../random_resistor_value_sml_091122v1p0.pdf

    Shawn

Reply
  • ShawnLogan
    in reply to lukelukeamd

    Dear lukelukeamd,

    I am glad you found it interesting! I thought it might be worth including the ability to generate a Gaussian distribution in addition to a uniform distribution and added that capability. THe updated script directory and documentation has been updated. An example of the simulated distributions using the uniform and gaussian distribution options from page 14 of the note is shown below.

    www.dropbox.com/.../random_resistor_value_090922.zip

    www.dropbox.com/.../random_resistor_value_sml_091122v1p0.pdf

    Shawn

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