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7 votes
7 votes

4 Answers

4 votes
4 votes

 Delay for sum is 2*XOR = 2*20  = 40ms
 Delay for carry is 1xor+1and+1or=20+15+10=45 ns
in ripple-carry adder each adder must wait for the full output from the previous adder.
hence delay for S3= 3*45+40=175 ns
delayfor last carry= 4*45=180 ns
nd it is asking for stable o/p so it should b 180 ns .

edited by
3 votes
3 votes
If XOR= 20

AND= 15

OR=10

Shouldn't the answer be 4*45=180ns?
0 votes
0 votes

The question is straight out of Salivahanan! 
So the stable output is generated by the last carry bit C4 = 4 * Tp, the in this 4 bit binary adder, as the propagation delay is clearly (20+15+10)nsec  = 45nsec so,C4 = 4 * 45 = 180nsec 

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