Basic Gates Theory - Virtual Lab

Introduction

Logic gates are the basic building blocks of any digital system. Logic gates are electronic circuits having one or more than one input and only one output. The relationship between the input and the output is based on a certain logic. Based on this, logic gates are named as:

AND gate
OR gate
NOT gate
NAND gate
NOR gate
Ex-OR gate
Ex-NOR gate

1. AND Gate

The AND gate is an electronic circuit that gives a high output (1) only if all its inputs are high. A dot (.) is used to show the AND operation i.e. A.B or can be written as AB

AND Gate Logic Symbol — Logic Symbol of AND Gate

AND Gate Truth Table — Truth Table of AND Gate

A simple 2-input logic AND gate can be constructed using IC 7408

2. OR Gate

The OR gate is an electronic circuit that gives a high output (1) if one or more of its inputs are high. A plus (+) is used to show the OR operation.

Y = A + B

OR Gate Logic Symbol — Logic Symbol of OR Gate

OR Gate Truth Table — Truth Table of OR Gate

A simple 2-input logic OR gate can be constructed using IC 7432

3. NOT Gate

The NOT gate is an electronic circuit that produces an inverted version of the input at its output. It is also known as an inverter. If the input variable is A, the inverted output is known as NOT A. This is also shown as A' or A with a bar over the top.

Y = A'

NOT Gate Logic Symbol — Logic Symbol of NOT Gate

NOT Gate Truth Table — Truth Table of NOT Gate

A simple 1-input logic NOT gate can be constructed using IC 7404

4. NAND Gate

This is a NOT-AND gate which is equal to an AND gate followed by a NOT gate. The outputs of all NAND gates are high if any of the inputs are low. The symbol is an AND gate with a small circle on the output. The small circle represents inversion.

Y = AB

NAND Gate Logic Symbol — Logic Symbol of NAND Gate

NAND Gate Truth Table — Truth Table of NAND Gate

A simple 2-input logic NAND gate can be constructed using IC 7400

5. NOR Gate

This is a NOT-OR gate which is equal to an OR gate followed by a NOT gate. The outputs of all NOR gates are low if any of the inputs are high. The symbol is an OR gate with a small circle on the output. The small circle represents inversion.