OLevel

## Logic Gates

Logic Gates

### Logic Gates

• Logic gates take binary inputs and produce a binary output.
• The values it deals with are 0 and 1 or on and off.
• The binary states are the electrical voltage states, i.e. 0 represents an ON state and 1 represents an OFF state.
• Multiple logic gates are used to create a logic circuit.
• Logic gates are a crucial element of a logic circuit.
• Different logic gates have different characteristics.
• Truth Tables are used to verify the outputs of the logic gates.

### Six (6) Types of Logic Gates:

• This figure illustrates the symbols of different logic gates.

### 1.NOT Gate:

• NOT Gate is the most simple logic gate.
• It takes a single input and inverts the value.
• If an input is 0, NOT will make it a 1 and vice versa.
• It is represented by

Truth Table:

### 2.AND Gate:

• AND Gate produces ‘1’ as an output only and only if all inputs are ‘1’.
• If anyone input is '0' then the result will be '0'.
• It is represented by A.B.

Truth Table:

### 3.OR Gate:

• OR Gate produces ‘1’ in output if a single input is 1.
• It produces a ‘0’ in output only if both inputs are ‘0’.
• It is represented by a ‘+” sign.

Truth Table:

### 4.NAND Gate:

• It is also known as the NOT AND Gate.
• It is the reverse of AND Gate.
• It gives ‘1’ in output if and only if A and B both are NOT ‘1’.

Truth Table:

### 5.NOR Gate:

• It is also known as NOT OR Gate.
• It is the reverse of OR Gate.
• It produces ‘1’ in output if NOT a single input is 1.

Truth Table:

### 6.XOR Gate:

• It is also known as Exclusive OR Gate.
• It produces ‘1’ in output if, (A is ‘1’ AND B is ‘0’) OR (A is ‘0’ AND B is ‘1’).

Truth Table:

### Logic Circuits:

• Logic circuits are created by connecting logic gates together.
• These circuits are created to perform a particular function.
• A logic circuit truth table is required to understand its function’s nature.

### How to Create a Logic Circuit Truth Table:

It is considerably complicated to create a logic circuit truth table.
But if you follow the steps defined below, it will become easy for you to make it yourself.

### Steps:

1. First, add temporary output letters after each logic gate in a circuit as shown below:

2. Now find out the values of these new letters first i.e. K,L & M.
3. As you can see from the figure, that K is NOT A.
4. L is the output of A OR
5. M is the output of K AND L.
6. And the final output will be M AND L.
7. This can also be written in the equation as X =
8. Therefore, it is advisable to solve in the same sequence and you will get your truth table easily.

Note: Just as you can make a boolean equation by seeing the logic circuit you can also create a logic circuit from the equation.

Practice Exercise: Create a logic circuit and truth table for the following: