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WHAT'S YOUR ENGINEERING QUOTIENT?

Problem 4—Design a half-adder circuit using just five 2-input NAND gates.

The definition of a half-adder is this: Given two inputs A and B, the outputs are:

Sum = A XOR B

Carry = A•B

The following figure shows the half-adder built with five NAND gates.

The output of the gate 1 is (A•B)'.

The output of gate 2 is ((A•B)')' = A•B, which is the required Carry.

The output of gate 3 is ((A•B)'•A)' = (A•B')'

The output of gate 4 is ((A•B)'•B)' = (A'•B)'

The output of gate 5 is ((A•B')'•(A'•B)')' = A•B' + A'•B, which is the required Sum.

Contributor: Naveen P N

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