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Different between normal buffer and clock buffer?

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bradyue

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clock buffer

i've read some articals about the benefit of clock buffer... such as equal duty cycle for rise and fall time ...
but when i look up in the library manu, it is just the contrary....
the difference between rise delay and fall delay for nomal buffer is even smaller than clock buffer....
how to explain this?
 

Daniel M.E. Lee

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clock buffer vs normal buffer

When we use clock buffer, its purpose is to equal duty cycle for all f/f.
whereas, when we use normal buffer, its purpose is to meet timing.

The timescale of normal buffer is smaller than clock buffer.
Normal buffer is related with set-up/hole timing violation.

The timescale you can fix using normal buffer is too small.
Comparing with that, clock buffer's timescale is larger.
As you can guess in design compiler constraint, clock uncertainty is 0.2 or 0.3 ns.
If your design's clock uncertainty meets the above range, it's okay.
So clock buffer and normal buffer have diffierent timescale to handle.

It's not fact, but i'm just guessing with my back ground.

Thank you!
 

iwpia50s

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difference between clock buffer and normal buffer

Clock buffers are designed to have symmetric rise and fall times so that when cts is run there is no need to be concerned about duty cycle degradation. Whereas regular buffers are not necessarily balanced but designed for a certain drive strength.
 

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