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Combinational Delay in Frequency Calculation

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spartanthewarrior

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Hi All,

F(max) = 1/ (Tsu + Tpd + Tc)

Tsu --> set up time

Tpd --> Propogation Delay

Tc --> Combinational Delay

Quesiton: I we don't have combinational logic in between two flip flop's. Then do we consider routing delay or How to calculate combinational delay value.

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shelby

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Since there is no combinational logic, Tc=0. The length routed net between the flops will effect it's capacitance, but this will be reflected in the Tpd delay.
 

jaydip

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@Shelby
U sure about this? there will not be any routing delay?
 

shelby

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Yes, if there is a large resistance on the net, it could effect the delay as well. But this is normally a fraction of the overall delay. This would exist on nets between combinational elements as well.

The original equation was basic and didn't account for other factors like skew, slew, SI or other required margins, so I tried to keep it simple :)
 

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