Question

Which one of the following logic gates is universal logic gate?

• A. OR
• B. AND
• C. NOT
• D. NAND

Hint:

Remember that there are two universal logic gates: \textbf{NAND} and \textbf{NOR}. If a question asks for a universal gate, the answer will always be one of these two.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
A universal logic gate is a logic gate that can be used, by itself, to implement any other type of logic function or logic gate.
Step 2: Detailed Explanation:
The basic logic gates are AND, OR, and NOT. These can be combined to create any digital logic circuit.
However, it has been shown that either the NAND gate or the NOR gate can be used to construct all three basic logic gates:
- NOT gate from NAND: Connect both inputs of a NAND gate together.
- AND gate from NAND: Follow a NAND gate with a NOT gate (which is another NAND gate).
- OR gate from NAND: Use three NAND gates according to De Morgan's theorem.
Because any logic function can be built using only NAND gates, the NAND gate is considered a universal gate. The same is true for the NOR gate.
The basic gates OR, AND, and NOT are not universal because, for example, you cannot create an AND gate using only OR gates.
Step 3: Final Answer:
Out of the given options, the NAND gate is a universal logic gate. Therefore, option (D) is correct.