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Hold time pass on FF, but failed on TT?

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jaxshai

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Is it possible to pass the hold time check on Best Corner, but failed on Typical corner?
Any one can help me out?

Thank in advanced
Jax
 

avimit

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Yes, it is possible.
In Best corner, data delay between flops in minimum, so you would expect hold to fail on this corner, and since the data delay between flops increases in typ corner, you wud expect hold to pass on it, if it has passed on Best Corner.
BUT
in a postlayout netlist, it may be possible that in typ corner, the delay in clock buffers is increased more than the data delay between the flops, so under these circumstances the clock is delayed and the data is not(as much as the clock), so your hold may fail on typ corner, even though it passes on best corner
Kr,
Avi
http://www.vlsiip.com
 

jaxshai

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Thanks, avi.
I agree your description above.

However, for project timing sign off condition. Is it necessary to take Typical corner as one sign off condition, if the foundry just recommend to do worst/best, worst LT/best HT as sign off condition?
 

avimit

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Yes, it is necessary, even if the foundary doesn't mention it, I will pass my sta on best/typ/worst corners.
The fix for your problem is not difficult, just insert some more buffers in the failing path, and it would be fine
Kr,
Avi
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    jaxshai

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jaxshai

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Thanks for sharing your experience and it helps.

BR
Jax
 

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