Logic Gates

A logic gate is a device that acts as a building block for digital circuits. They perform basic logical functions that are fundamental to digital circuits. Most electronic devices we use today will have some form of logic gates in them. For example, logic gates can be used in technologies such as smartphones, tablets or within memory devices.

Logic gates are the basic building blocks of any digital system. It is an electronic circuit 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 etc.

AND Gate

A circuit which performs an AND operation is shown in figure. It has n input (n >= 2) and one output.

Function: The AND gate gives a high output (1) only when all inputs are high (1). If any input is low (0), the output is low (0).

AND gate

Logic diagram

AND Logical Diagram

Truth Table

AND Truth Table

OR Gate

A circuit which performs an OR operation is shown in figure. It has n input (n >= 2) and one output.

Function: The OR gate gives a high output (1) if at least one input is high (1). The output is low (0) only when both inputs are low (0)
OR gate

Logic diagram

OR Logical Diagram

Truth Table

OR Truth Table

NOT Gate

NOT gate is also known as Inverter. It has one input A and one output Y.

  • Function: The NOT gate is also known as an inverter. It gives a high output (1) if the input is low (0) and a low output (0) if the input is high (1).

    • NOT gate

    Logic diagram

    NOT Logical Diagram

    Truth Table

    NOT Truth Table

    NAND Gate

    A NOT-AND operation is known as NAND operation. It has n input (n >= 2) and one output.

    • Function: The NAND gate is the inverse of the AND gate. It gives a high output (1) unless all inputs are high (1), in which case the output is low (0).

    NAND gate

    Logic diagram

    NAND Logical Diagram

    Truth Table

    NAND Truth Table

    NOR Gate

    A NOT-OR operation is known as NOR operation. It has n input (n >= 2) and one output.


    Function: The NOR gate is the inverse of the OR gate. It gives a high output (1) only when both inputs are low (0). If any input is high (1), the output is low (0).


    NOR gate

    Logic diagram

    NOR Logical Diagram

    Truth Table

    NOR Truth Table

    XOR Gate

    XOR or Ex-OR gate is a special type of gate. It can be used in the half adder, full adder and subtractor. The exclusive-OR gate is abbreviated as EX-OR gate or sometime as X-OR gate. It has n input (n >= 2) and one output.

    XOR gate

    Logic diagram

    XOR Logical Diagram

    Truth Table

    XOR Truth Table

    XNOR Gate

    XNOR gate is a special type of gate. It can be used in the half adder, full adder and subtractor. The exclusive-NOR gate is abbreviated as EX-NOR gate or sometime as X-NOR gate. It has n input (n >= 2) and one output.

    XNOR gate

    Logic diagram

    XNOR Logical Diagram

    Truth Table

    XNOR Truth Table


    Application of Logic Gates

    Logic gates have a lot of applications, but they are mainly based on their mode of operations or their truth table. Basic logic gates are often found in circuits such as safety thermostats, push-button locks, automatic watering systems, light-activated burglar alarms and many other electronic devices.

    One of the primary benefits is that basic logic gates can be used in various combinations if the operations are advanced. Besides, there is no limit to the number of gates that can be used in a single device. However, it can be restricted due to the given physical space in the device. In digital integrated circuits (ICs), we will find an array of the logic gate area unit.