The Gateway to Computer Science Excellence
+1 vote

In a $8$-bit ripple carry adder using identical full adders, each full adder takes $34$ns for computing sum. If the time taken for $8$-bit addition is $90$ ns, find time taken by each full adder to find carry.

  1. $6$ ns
  2. $7$ ns
  3. $10$ ns
  4. $8$ ns
in Digital Logic by Boss (25.1k points)
edited by | 179 views

1 Answer

+2 votes
Sum in ripple carry adder is --> $max( Sum, Carry)$ $for$ $MSB+$ $delay$ $to$ $produce$ $carry$ $of$ $N-1bits$

now given sum takes $34ns$ it can be clearly seen that for the last bit $Max(sum,carry)$ is $sum$ only

So the carry generation for $N-1=8-1=7bits$ has taken $90-34=56ns$

so time to produce carry $\dfrac{56}{7}=8ns$

$D$ $is$ $the$ $answer$
by Junior (549 points)
Quick search syntax
tags tag:apple
author user:martin
title title:apple
content content:apple
exclude -tag:apple
force match +apple
views views:100
score score:10
answers answers:2
is accepted isaccepted:true
is closed isclosed:true
50,833 questions
57,713 answers
107,684 users