Question

How many two-input NAND gates are required to produce a two-input exclusive OR (XOR) gate?

a) 1
b) 2
c) 3
d) 4

Answer 1

To produce a two-input XOR gate, four NAND gates are required. The implementation involves using the NAND gates to create NOT, AND, and OR functions, which are then combined to form the XOR gate.

Step-by-step explanation:

To create a two-input exclusive OR (XOR) gate using two-input NAND gates, we need four NAND gates. The logic of the XOR function can be implemented by first creating the intermediary negation, OR, and AND functions using NAND gates, then combining them to result in the XOR function. The basic configurations for creating an XOR gate from NAND gates are:

• A NAND gate can be used as a NOT gate by connecting both inputs to the same signal.
• Two NAND gates are used to create an AND gate.
• Three NAND gates can be used to create an OR gate.

Based on these configurations, we need four NAND gates to implement an XOR gate:

1. Two NAND gates configured as NOT gates to invert both inputs.
2. One NAND gate configured as an AND gate by connecting the outputs of the two NOT gates.
3. One NAND gate to act as an OR gate that takes the original inputs and the output of the AND gate.

The correct answer to the question is thus d) 4.