How to decide derating value?

[srshankar]

Hi,

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


Thanks,
Ravi Shankar.

 

[rahul.achates]

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

 

[srshankar]

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

 

[rahul.achates]

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