How to decide derating value?

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srshankar

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Hi,

Could somebody explain how derating values are calculated in OCV analysis and AOCV analysis?


Thanks,
Ravi Shankar.
 

derating value is depend on your library , it also depend on your clock uncertainty.

But clock uncertainty and derating , both are different thing.

Normally , we put 10% for -early and 20% for -late

set_derate_timing -early 0.9
set_derate_timing -late 1.2

Rahul
 

Hi Rahul,

But Rahul, I have a confusion in, how specific value (10% or 20%) is decided. What is to be done to arrive at particular derating value(0.9 and 1.2)?



Thanks,
Ravi Shankar
 

Hi Ravi,

Those are typical numbers used in STA, however you can change those number based on result you are getting from STA.

For example - if you are getting too many timing violations then you can reduce those number little bit.

also its depend of max frequency of design , uncertainty you have specified , that is also a margin.

Rahul
 

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