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A 16-bit ripp...

Question

A 16-bit ripple carry adder is realized using 16 identical full adders (FA) as shown in the figure. The carry-propagation delay of each FA is 12 ns and the sum-propagation delay of each FA is 15 ns. The worst case delay (in ns) of this 16-bit adder will be

195

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Solution

The correct option is A 195
Full adder is a combinational circuit that performs the sum of three bits i.e. add two bits and a carry from previous addition and produces output as sum and carry.
Given carry propagation delay of each
FA= 12 nsec.
Sum-propagation delay of each FA = 15 nsec.

It can be seen from above diagram, full adder is not received from previous full adder.
So, in 16-bit ripple carry adder, worst case delay of this 16-bit adder will be
= (15 x 12) nsec. + 15 nsec.
= 195 nsec.

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