Logic gates serve as the fundamental components of all digital systems. These electronic circuits have one or more inputs and a single output, with the output determined by a specific logical relationship between the inputs. Examples of such gates include the AND, OR, NOT, NAND, and NOR gates, each named according to the logic they implement.

## What is a Logic Gate?

A logic gate is an electronic circuit that performs logical operations inside a digital device. A logic gate is made by the combination of a resistor, diode, and transistor. A Logic gate receives one or multiple inputs and gives only one output. It takes input and performs logical operations. **Boolean algebra **is the base for logical operation in digital devices. Boolean algebra consists of two states – true or false.** In a binary system true is represented as 1 and false is represented as 0**.

## Types of Logic Gates

Logic gates are classified into four major types. They are given below:

- Basic logic gate
- Universal gate
- Exclusive gate
- Compound or complex gate

In this blog, we will learn about the first three types of logic gates.

## Basic logic gates

There are three types of basic logic gates used in digital devices:

- AND GATE
- OR GATE
- NOT GATE

### AND GATE

#### Definition

An AND gate can take two or more inputs and deliver one output. It only gives output logic 1 when all the inputs are logic 1. If an input is logic 0 the output will be logic 0.

Boolean expression of 2-input AND gate is:

**Y = A.B**

Boolean expression of n number of input AND gate is:

**Y = A.B.C.D…**

Where A, B, C, D are the inputs and Y is the output.

#### Truth Table

The truth table of two inputs AND gate is given below:

A(1^{st} input) | B(2^{nd} input) | Y(output) |
---|---|---|

0 | 0 | 0 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 1 |

#### Symbol

The symbol of the AND gate is:

#### Example

IC 7408 is an example of an AND gate. It has four 2-input AND gates inside it.

### OR GATE

#### Definition

OR gate can take two or more inputs and only give one output. It only returns output logic 0 if all the inputs are logic 0. If only one input is logic 1 the output will be logic 1.

Boolean expression of 2-input OR gate is:

**Y = A + B**

Boolean expression of n number of input OR gate is:

**Y = A + B + C + D +…**

Where A, B, C, D are the inputs and Y is the output.

#### Truth Table

The truth table of two inputs OR gate is given below:

A(1^{st} input) | B(2^{nd} input) | Y(output) |
---|---|---|

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 1 |

#### Symbol

#### Example

IC 7432 is an example of OR gate which has four 2-input OR gates.

### NOT GATE

#### Definition

NOT gate can take only one input and give one output. It converts logic 1 to logic 0 and logic 0 to logic 1. That’s why it is also called an **inverter**.

Boolean expression of NOT gate is:

Where A is the input and Y is the output. The bar(‘ over the input A means NOT operation for input A.

#### Truth Table

The truth table of NOT gate is given below:

A(1^{st} input) | Y(output) |
---|---|

0 | 1 |

1 | 0 |

#### Symbol

The symbol of the NOT gate is:

#### Example

For example, we can consider IC 7404 which has 6 NOT gates.

## Universal Gates

There are two types of universal gates. They are:

- NAND GATE
- NOR GATE

All kinds of logic circuits can be implemented using only one type of universal gate. For that reason, they are called universal gates.

### NAND GATE

#### Definition

NAND gate is the combination of an AND gate followed by a NOT gate. It performs the opposite operation of the AND gate. It can take two or more inputs and only one output. Boolean expression of 2-input NAND gate is:

Boolean expression of n number of input NAND gate is:

Where A, B, C, D are inputs and Y is the output.

#### Truth Table

The truth table of the 2-input NAND gate is given below:

A(1^{st} input) | B(2^{nd} input) | Y(output) |
---|---|---|

0 | 0 | 1 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 0 |

#### Symbol

The symbol of the NAND gate is:

#### Example

IC 7400 is an example of NAND gate that contains four 2-input NAND gates.

### NOR GATE

#### Definition

NOR gate does the opposite operation of the OR gate. NOR gate can be implemented by one OR gate followed by a NOT gate. It can take two or more inputs and give only one output. It gives output logic 1 if all the inputs are logic 0. If an input is logic 1 then the output will be logic 0.

Boolean expression of 2-input NOR gate given below:

Boolean expression of n number of input NOR gate is given below:

Where A, B, C, D are inputs and Y is the output.

#### Truth Table

The truth table of the 2-input NOR gate is given below:

A(1^{st} input) | B(2^{nd} input) | Y(output) |
---|---|---|

0 | 0 | 1 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 0 |

#### Symbol

The symbol NOR gate is given below:

#### Example

IC 7402 is an example of NOR gate. This IC has four 2-input NOR gates.

## Exclusive Gates

There are two exclusive gates available. They are:

- XOR GATE
- X-NOR GATE

### XOR GATE

#### Definition

XOR gate can only take two inputs and produce one output. 2-input XOR gate gives output logic 1 if two inputs are in different logic states. It also produces output logic 1 if there are an odd number of inputs in logic 1.

Boolean expression of the XOR gate is given below:

Where A and B are the input and Y is the output.

#### Truth Table

The truth table of the XOR gate is given below:

A(1^{st} input) | B(2^{nd} input) | Y(output) |
---|---|---|

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 0 |

#### Symbol

#### Example

IC 7486 is an example of the implementation of XOR gate. It has four 2-input XOR gates.

### X-NOR GATE

#### Definition

X-NOR gate does the opposite operation of the XOR gate. It can be implemented using one XOR gate followed by a NOT gate. It produces output logic 1 if two inputs are in the same logic state.

Boolean expression of the X-NOR gate is given below:

Where A and B are the inputs and Y is the output.

#### Truth Table

A(1^{st} input) | B(2^{nd} input) | Y(output) |
---|---|---|

0 | 0 | 1 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 1 |

#### Symbol

The symbol of the X-NOR gate is given below:

#### Example

IC 74266 is an example of X-NOR gate. It has four 2-input X-NOR gates.

## Recap

A recap of all types of logic gates is given below:

**Logic Gate**: Eelectronic circuits in a digital system that perform logical operations on input and give an output.**Types of Logic Gates**:**Basic Gates**: AND gate, OR gate, NOT gate.**AND**: Output is 1 only if all inputs are 1.**OR**: Output is 1 if any input is 1.**NOT**: Output is the opposite of input.

**Universal Gates**: NAND gate and NOR gate. Each universal gate Can implement all types of logic circuits.**NAND**: Opposite of AND gate.**NOR**: Opposite of OR gate.

**Exclusive Gates**: XOR gate and XNOR gate.**XOR**: Output is 1 if inputs are different (for 2-input).**XNOR**: Output is 1 if inputs are the same (for 2-input).