In combinational logic terminology, which statement correctly describes a half-adder?

Introduction / Context:
A half-adder is a fundamental building block for arithmetic in digital systems. It adds two one-bit inputs and produces two outputs: the sum and the carry. Recognizing its correct composition is essential before moving on to full adders and ripple/CLA adder architectures.

Given Data / Assumptions:

• The half-adder has two inputs: A and B.
• Outputs are SUM and CARRY.
• We are identifying whether any single standard gate alone (AND, NAND, NOR, EX-OR) equals a half-adder.

Concept / Approach:
A half-adder is implemented with two distinct functions: SUM = A XOR B, and CARRY = A AND B. No single standard gate can provide both outputs simultaneously. Therefore, while XOR is part of the half-adder (for SUM), the half-adder is not “also known as” an XOR circuit; it requires both XOR and AND working together as a pair.

Step-by-Step Solution:

Verification / Alternative check:
Truth table method: List all input combinations (00, 01, 10, 11). SUM column equals XOR of inputs; CARRY equals AND. This cannot be achieved by a single standard gate for both outputs, confirming “None of the above.”

Why Other Options Are Wrong:

Common Pitfalls:
Equating “half-adder” with “XOR” because the SUM expression is XOR; always remember the carry output requires an AND path.

Final Answer:
None of the above