carry look ahead adder vs ripple carry

Question

$Exclusive-OR$ gate has a propagation delay of $10$ ns and that the $AND$ or $OR$ gates have a propagation delay of $5$ ns.What is the total propagation delay time in the four-bit adder.Assume $FAN-IN =2$

$1)$ ripple adder

$2)$ carry look ahead adder

Comments

Kindly mention the FAN IN of the logical gates to be used.

Answer 1

1. Ripple carry adder
Tcarry= 4*(5+5)=40
Tsum=(4-1)*(5+5)+2*10=50
Total propagation delay=40+50=90 ns

Carry look ahead adder

TSUM = Pi+Ci

.              = Exor+ and+or+exor gate  time

.              = 10+5+5+10=30 ns

 

Comments

I guess answer is 80 for RCA.

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Can u plzz elaborate little bit

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@iarnav getting same 80 for rca

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I think 3*20 + 20 =  80 for RCA