Logic Gates

There are mainly 7 types of logic gates that are used in expressions. By combining them in different ways, you will be able to implement all types of digital components. Take a look at each basic logic gate and their operation.

• NOT Gate/Inverter

As the name suggests, this gate is used to produce the inverted output. This is the simplest gate with single input single output logic. The logic symbol and truth table is shown below. When a 0 [LOW] is given to the input, the output will be a 1 [HIGH]. If a HIGH input is given, the output will be LOW.

NOT Gate Symbol

Truth Table-NOT Gate

• AND GATE

In this type of a logical gate, there can be 2 or multiple number of inputs. The operation performed by the gate is called the “AND” operation. The logic symbol and truth table is shown below. A 2-input AND gate is shown below. If both the inputs A and B are HIGH, then the output will also be HIGH. If both of them or any one of them is low, then the output will also be low.

AND Gate

Truth Table-AND Gate

• OR GATE

In this type of logic gate, the operation carried out by the gate is called “OR” operation. The logic symbol and truth table is shown below. A 2-input OR gate is shown below. If any one of the input or both the inputs are HIGH, then the output will be HIGH. If both the inputs are LOW, then the output will also be low.

OR Gate

Truth Table-OR Gate

• NAND Gate and NOR Gate

Since you have understood the working of AND Gate, OR Gate, and NOT gate, it is easy to understand the working of NAND and NOR gate as well. A NAND Gate is just a combination of an AND gate and a NOT Gate. The logic symbol and truth table is shown below. The output will be just the opposite of a AND Gate. That is, if both the inputs are HIGH, the output will be LOW. If both the inputs are LOW, or any one of them is LOW, the output will be HIGH.

NAND Gate

Truth Table-NAND Gate

A NOR Gate is a combination of an OR Gate and a NOT Gate. The logic symbol and truth table is shown below. The output will be just the opposite of a OR Gate. That is, if any one of the input or both the inputs are HIGH, then the output will be LOW. If both the inputs are LOW, then the output will be HIGH.

NOR Gate

Truth Table-NOR Gate

These two gates are commonly referred to as the Universal Gates, because either one of them can be used to create the basic AND, OR and NOT gate.

• EXOR Gate and EXNOR Gate

In an EXOR Gate, if both the inputs are HIGH, or if both the inputs are LOW, the output will be LOW. If any one of the two inputs is HIGH, the output will be HIGH. The logic symbol and truth table are shown below.

EXOR Gate

Truth Table-EXOR Gate

An EXNOR Gate will be just the opposite of an EXOR Gate. That is, if both the inputs are HIGH, or if both the inputs are LOW, the output will be HIGH. If any one of the two inputs is HIGH, the output will be LOW. The logic symbol and truth table are shown below.

EXNOR Gate

Truth Table-EXNOR Gate

Usually XOR Gate is not included in the list because the logic can be easily implemented with the help of the other gates.  An easy implementation using the AND Gate, OR Gate and the NOT Gate is shown below