Question

Define CMOS XOR gate and its logic operation.

Answer 1

CMOS (Complementary Metal-Oxide-Semiconductor) XOR gate is a type of digital logic gate that performs the exclusive OR (XOR) operation. The XOR gate takes two binary inputs, and its output is HIGH (1) when the number of inputs that are HIGH is odd, and it is LOW (0) when the number of inputs that are HIGH is even.

The truth table for the XOR gate is as follows:

Input A    Input B    Output
0    0    0
0    1    1
1    0    1
1    1    0

The logic operation of the XOR gate can be represented using the following Boolean expression:

Output = A ⊕ B

where "⊕" represents the XOR operation.

In CMOS technology, an XOR gate is implemented using a combination of NMOS (n-channel metal-oxide-semiconductor) and PMOS (p-channel metal-oxide-semiconductor) transistors. The circuit ensures efficient power consumption and fast switching characteristics.

If both inputs A and B are LOW (0), both NMOS and PMOS transistors are turned off, and the output is pulled HIGH (1) through a pull-up resistor. If one of the inputs (A or B) is HIGH (1), the corresponding transistor turns ON, allowing the output to be pulled LOW (0). If both inputs are HIGH (1), both NMOS and PMOS transistors are ON, but they create a complementary path, so the output is pulled back to HIGH (1) through the pull-up resistor. This configuration results in the correct XOR behavior as described in the truth table.