# What are logic gates and truth table :

In digital electronics, logic gates are certain type of physical devices basically used to express the Boolean functions. The truth table is a tabular representation of a logical expression. It shows the outputs generated from various combinations of input values. Truth tables are also used to represent Boolean functions. In this article, we will discuss different logic gates and truth table for each logic gates.

The logic gates have one or more than one inputs and produce only one output. The output of a logic gate depends on some certain logical behaviour of that logic circuit. Based on these logical behaviour that a Gate has, logic gates are named as AND Gate, OR Gate & NOT Gate.

AND Gate, OR Gate & NOT Gate are the three basic Gates. Using these three basic gates we can also construct four more Gates – NAND Gate, NOR Gate, XOR Gate & XNOR Gate. Each output and output of a logic gate is represented by binary conditions 0 (LOW) and 1 (HIGH). In most of the cases binary LOW is represented using the Zero Volts (0 V), while the HIGH state is represented using the positive 5 Volts (+5V).

## Digital logic gates and truth table :

## AND Gate :

AND Gate performs the logical AND operation. It accepts the combination of two or more input variables and performs multiplication of those input variables to provide a single output signal.

### Block Diagram of AND Gate

## Truth Table of AND Gate

According to the above truth table, an AND Gate produces the HIGH (1) output only when both of the inputs are HIGH else it produces a LOW output.

## Pin diagram of AND Gate

## OR Gate :

OR Gate performs the addition operation between the two or more binary input variables. An OR Gate consists of two or more inputs and produces one output which is the sum of all those binary input variables.

### Block diagram of OR Gate.

### Truth table of OR Gate

Above truth table shows that an OR Gate produces a LOW output only when both of the inputs are LOW, else it produces a HIGH output.

### Pin diagram of OR Gate

## NOT Gate :

NOT Gate performs the operations like a logical inverter. So output will be the complement of the input. NOT Gate has a different behavior as compared to other gates since it contains only one input signal.

### Block diagram of NOT Gate

### Truth table of NOT Gate

### Pin diagram of NOT Gate

## NAND Gate :

NAND gate performs the combinational operations of AND Gate & NOT Gate. It is formed by using an AND Gate followed by a NOT Gate. A NAND Gate may also have two or more inputs and produces only one output.

### Block diagram of NAND Gate

### Truth table of NAND Gate

As stated in the truth table, an NAND Gate produces LOW output only when both of the inputs are HIGH. Otherwise it always produces a HIGH output.

### Pin diagram of NAND Gate

## NOR Gate :

NOR Gate is the combinational operations of OR Gate followed by a NOT Gate. It may have two or more inputs and produces only one output.

### Block diagram of NOR Gate

### Truth table of NOR Gate

Its truth table shows that, the NOR Gate produces output HIGH only when the both of the inputs are LOW. Otherwise it always produces a LOW output.

### Pin diagram of NOR Gate

## XOR Gate (Exclusive OR gate) :

This Gate works like the logical either OR. XOR Gate contains two or more than two inputs and converts them to a single output signal; it is a special type of Gate which holds some special behaviour. It is generally used to construct Adder and Subtractor.

### Block diagram of XOR gate

### Truth table of XOR gate

XOR Gate truth table says that when both of the inputs are same then it produces a LOW output otherwise it produces a HIGH output.

### Pin diagram of XOR gate

## XNOR Gate (Exclusive NOR) :

XNOR or Exclusive NOR Gate is a combination of XOR Gate followed by an inverter i.e. a NOT Gate. It accepts two or more input signals and converts them to produce a single output signal.

### Block diagram of XNOR Gate

### Truth table of XNOR Gate

XNOR Gate gives output HIGH when both of the inputs are same otherwise it always produces a LOW output.

### Pin diagram of XNOR Gate

## Uses of logic gates :

Digital systems are constructed using these logic gates. Using the various combinations of these logic gates, complex of complex circuit can be designed to perform different operations. We can combine unlimited number of logic gates in a single chip to perform such Complex operations.

**Also check:** **Components of CPU & their Functions**

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