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$Exclusive-OR$ 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

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

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

TSUM = Pi+Ci

.              = Exor+ and+or+exor gate  time

.              = 10+5+5+10=30 ns

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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

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In a $4-$bit carry look ahead adder, the propagation delay of EX-OR gate is $20ns,$ AND and OR gates is $10ns.$ The sum and carry output of full adder takes $20ns$ and $10ns$ respectively. The total propagation delay of the above adder in $ns$ is