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Current Density Value

maven7783

Hi,

As i was doing the calculations for power stripe width calculations, i got  struck at current density value.

From where do we get that, as of i know it will come from the foundry tech file.

Will it be included in the tech lef what we use in P&R.

thanks,

Maven. 

 

 

  • Sometimes the current density numbers are in the tech LEF, and sometimes you have to add them yourself from the design rule manual. (And sometimes they are incorrect in the LEF, so it's best to always double-check with the process design rule manual.) The section in the LEF would look something like this, for each metal layer:

        ACCURRENTDENSITY    RMS
            FREQUENCY       500 ;
            WIDTH           0.090   0.180   0.500   1.000   5.000   12.000 ;
            TABLEENTRIES    14.937  13.728  11.657  10.738  9.830   9.682 ;

    The command to check for current density violations is verifyACLimit. However, this is only for signal nets. To check the current density for pwr/gnd nets, you will need to use EPS or vstorm and run the "rj" check. I'm not sure about EPS, but vstorm does not use the values in the tech LEF. You will have to create "model" statements to include in the vstorm command file.

    If you're just trying to calculate what the allowed density is based on width, so you can pick a width for your power grid, then use the numbers in the design rule manual. 

    Hope that helps,

    - Kari

  • Thank You very much Kari.

    I got the values from LEF as you said.

    thanks again. :)

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