@anusha it hink last ex-or gate for carry should b or gate https://gateoverflow.in/8250/gate2015-2_48
180 should be right answer.
plz comment if not agree!
??? wrong ??
Or wait for full output <S,C> of prev adder?
as they mentioned ripple carry addr , i think we need to wait until one full adder completely gives the output simila ques https://gateoverflow.in/8250/gate2015-2_48 here accordin to oficial key we need to assume that we can do 2nd full adder only when first full adder gives the complete o/p
Please check it:
If all are full adders:
First adder will give Sum after 40 nsec and Carry after 45 nsec ;
total delay = 4×45 = 180
If we choose first adder as half adder (as no need to add carry) : delay= 15+3×45 = 150 nsec
(because they have not mentioned all are full adder)
see this https://gateoverflow.in/8250/gate2015-2_48
yes @Debashish and @Arjun sir
according to every official site of IIT's about ripple carry adder, they are doing the same as what Debashish has done
So, 120 is correct ans
ref: http://iitkgp.vlab.co.in/?sub=38&brch=120&sim=483&cnt=664
and other webside mentioned the question in another way what about this one?
This is the actual GATE Question, all are Full Adders
Answer given is 50 in the Key
https://drive.google.com/file/d/0ByPcpxjSfRuVVWd4c184YWJuUEk/view
https://drive.google.com/file/d/0ByPcpxjSfRuVTldxaDBWUE45ZE0/view
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 .
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
The answer should be 50 ns.
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