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Resistance value mismatch (LVS mismatch) (Read 3118 times)
santosh_iitkgp
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Resistance value mismatch (LVS mismatch)
Mar 11th, 2008, 8:42pm
 
Hi,

I have designed a circuit using IHP technology (SG25H1M4) in cadence. In this circuit, I have used a rppd resister with a value of 260.143 Ohm, both in schematic and layout. Now, whenever I  am running the LVS, it shows a different value (14548 Ohm) for rppd resistor  used in layout.

Would you please tell me, why this is happening and how can it be solved.

Thanks,
Santosh.
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SANTOSH KUMAR PATNAIK
IIT KHARAGPUR, INDIA
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Geoffrey_Coram
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Re: Resistance value mismatch (LVS mismatch)
Reply #1 - Mar 12th, 2008, 11:58am
 
Did you check the layout, to make sure the length and width were what you expected?  (Measure them.)  You should then be able to estimate the resistance from the sheet rho in the model file.

Could be the LVS runset has a bug in the resistance calculation.  Put down a couple rppd devices with different numbers of squares and see if you get a consistent sheet rho -- and then try a couple different geometries with the same number of squares (L/W, 2L/2W, etc.).  You might get slightly different answers because you'll get more contacts with a double-wide device.
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