Worst Case Delay for Ripple Carry Adder

Thread Starter

d3ck

Joined Jul 14, 2013
8
I didn't get what my teacher said about worst case delay. The question sound like this:

Given 4-bit RCA with different delays, find the worst case delay for the adder

tcarry(0->1) = 400pS
tsum(0->1) = 500pS

tcarry(1->0) = 500pS
tsum(1->0) = 600pS



Since the RCA delay formula;
tadder = (N-1)tcarry + tsum

I assume carry will affect more to the overall delay. And my best guess is when A = 0101, B = 0101, worst delay will occurs because carry will change from 1 to 0 two times in the adding process. Am I correct?
 
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