Types of logic gates - SS2 ICT Lesson Note
Logic gates are crucial in digital circuit design, as they enable the manipulation of binary data and the execution of logical operations that form the foundation of all computation and data processing in modern electronics. There are several types of logic gates, each performing a specific logical operation:
AND Gate:
The AND gate produces an output of 1 only when all its input signals are 1. Otherwise, the output is 0. The AND gate produces a high (1) output only when all of its inputs are high (1). It performs the logical AND operation, and its symbol is like an intersection of inputs with a dot or the word "AND."
Truth Table:
|
Input A |
Input B
Output
0
0
0
0
1
0
1
0
0
1
1
1
OR Gate:
An OR gate generates an output of 1 if at least one of its input signals is 1. The output is 0 only when all inputs are 0. It performs the logical OR operation, and its symbol is like a curved shape or the word "OR."
Truth Table:
|
Input A |
Input B
Output
0
0
0
0
1
1
1
0
1
1
1
1
NOT Gate:
Also known as an inverter, the NOT gate has a single input and produces the opposite value at its output. If the input is 1, the output is 0, and vice versa.
Truth Table:
|
Input |
Output
0
1
1
0
XOR Gate (Exclusive OR):
The XOR gate produces an output of 1 when the number of input signals that are 1 is odd. If the number of input 1s is even, the output is 0. It performs the logical exclusive OR operation.
Truth Table:
|
Input A |
Input B
Output
0
0
0
0
1
1
1
0
1
1
1
0
NAND Gate (NOT-AND):
A NAND gate acts as an AND gate followed by a NOT gate. Its output is the inverse of the AND gate's output. It produces a low (0) output only when all of its inputs are high (1).
Truth Table:
|
Input A |
Input B
Output
0
0
1
0
1
1
1
0
1
1
1
0
NOR Gate (NOT-OR):
The NOR gate acts as an OR gate followed by a NOT gate. Its output is the opposite of the OR gate's output. It produces a high (1) output only when all of its inputs are low (0).
Truth Table:
|
Input A |
Input B
Output
0
0
1
0
1
0
1
0
0
1
1
0
XNOR Gate (Exclusive NOR):
The XNOR gate is the complement of the XOR gate. It produces an output of 1 when the number of input signals that are 1 is even.
Truth Table:
|
Input A |
Input B
Output
0
0
1
0
1
0
1
0
0
1
1
1
These logic gates can be combined to create more complex circuits that perform various logical functions. For instance, combining multiple gates can lead to the creation of adders, multiplexers, flip-flops, and other essential components used in digital systems.