Seven Fundamental Logic Gates in Digital Electronics

Understanding Logic Gates: Types and Functions

Logic gates are the fundamental building blocks in digital electronics. There are seven main types of logic gates used to perform various logical operations in digital systems. By combining different logic gates, complex operations are performed, and circuits like flip-flops, counters, and processors are designed. This article details the various types of logic gates.

Categories of Logic Gates

Logic gates can be broadly classified into three main categories:

• Basic Logic Gates (AND, OR, NOT)
• Universal Logic Gates (NAND, NOR)
• Special Purpose Logic Gates (XOR, XNOR)

AND Gate

An AND gate performs the logical multiplication of binary inputs. The output state of an AND gate will be high (1) if both inputs are high (1); otherwise, the output state will be low (0) if any input is low (0).

A · B = X

OR Gate

The OR gate is a widely used digital logic circuit. The output state of an OR gate will be high (1) if any input is high (1); otherwise, the output state will be low (0).

X = A + B

NOT Gate

In digital electronics, the NOT gate is one of the basic logic gates, having only a single input and a single output. It is also known as an inverter or inverting buffer. When the input signal is 'low,' the output signal is 'high,' and vice-versa.

Y = Ā or Y = A’

NOR Gate

The NOR gate is a universal logic gate. It takes two or more inputs and provides a single output. The output state of the NOR gate will be high (1) when all inputs are low (0). The NOR gate returns the complement of the OR gate's result. It is a combination of two basic logic gates: the OR gate and the NOT gate.

O = (A + B)’

NAND Gate

The NAND gate is another universal logic gate. The NAND gate, or 'Not AND,' is a combination of two basic logic gates: the AND gate and the NOT gate, connected in series. It takes two or more inputs and provides a single output. The output of the NAND gate will be high (1) when any of its inputs is low (0). Simply put, it performs the inverted operation of an AND gate.

X = (A · B)’

XOR Gate

In digital electronics, there is a specially designed logic gate, the XOR gate, which is used in digital circuits to perform a modulo sum. It is also referred to as an Exclusive OR gate or Ex-OR gate. It is used extensively in arithmetic logic circuits, logic comparators, and error detection circuits. The XOR gate can take only two inputs at a time and provide an output. The output of the XOR gate is high (1) only when its two inputs are dissimilar (i.e., if one is low (0) and the other is high (1)).

X = A’B + AB’

XNOR Gate

The XNOR gate is a combination of an XOR gate and a NOT gate. The output of the XNOR gate is high (1) when both inputs are high (1) or both are low (0). In other words, the output of the XNOR gate is high (1) when both inputs are the same. The XNOR gate can sometimes be called an Equivalence gate. In simple words, the XNOR gate is the complement of the XOR gate.

Y = A ⊙ B