Which logic gate provides an active high output only when all inputs are different?

Which logic gate provides an active high output only when all inputs are different?

• A. XOR
• B. AND
• C. OR
• D. NAND

Answer: (A)

This question tests how the XOR gate responds to input differences. For two inputs, the output of an XOR gate is high only when the inputs are different—one is 1 and the other is 0. That exactly matches the idea of having inputs that are not the same, giving an active high output only in that case. If there are more than two inputs, XOR behaves as a parity gate, producing a high output when an odd number of inputs are high, which isn’t the same as all inputs being different, so this distinction is usually understood best with two inputs. In contrast, an AND gate would require every input to be high, an OR gate would go high if any input is high, and a NAND is simply the inverted result of AND. So the gate that fits the description most directly for the common two-input case is the XOR.

This question tests how the XOR gate responds to input differences. For two inputs, the output of an XOR gate is high only when the inputs are different—one is 1 and the other is 0. That exactly matches the idea of having inputs that are not the same, giving an active high output only in that case. If there are more than two inputs, XOR behaves as a parity gate, producing a high output when an odd number of inputs are high, which isn’t the same as all inputs being different, so this distinction is usually understood best with two inputs. In contrast, an AND gate would require every input to be high, an OR gate would go high if any input is high, and a NAND is simply the inverted result of AND. So the gate that fits the description most directly for the common two-input case is the XOR.