In a 8-bit ripple carry adder using identical full adders, each full adder…
2020
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. ISRO 2020
- A.
6 ns
- B.
7 ns
- C.
10 ns
- D.
8 ns
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Correct answer: D
In an 8-bit ripple carry adder, the total addition time is determined by the delay of the first full adder plus the carry propagation delay through the remaining (n-1) stages.
Given: Total time (T_total) = 90 ns, Number of bits (n) = 8, First full adder time (T_first) = 34 ns.
Using the formula: T_total = T_first + (n - 1) × T_carry
Substituting the values: 90 = 34 + (8 - 1) × T_carry
Solving for T_carry: 90 - 34 = 7 × T_carry => 56 = 7 × T_carry => T_carry = 8 ns.
Therefore, the time taken by each full adder to find carry is 8 ns.
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