Logic Gates Definition, Types, Uses and Functions

Logic gates are the foundational elements of digital circuits. They process binary input 0s and1s to produce specific outputs based on predetermined rules. By interconnecting these gates in various configurations, complex digital systems and operations can be created and executed, enabling the vast array of digital devices and technologies we use today. Let's understand more!

Logic gates perform a specific logical function, processing one or more binary inputs to produce a single binary output. The output depends on the logic gate type and its inputs’ values.

The logic gate processes these inputs based on certain rules, defined by the type of the gate, to give a particular output.

Some Basic Terminologies:

• Input and Output: Logic gates operate using either 0 or 1 binary values. The count of these inputs can differ depending on the specific type of gate.
• Truth Table: This table illustrates every potential combination of inputs and the corresponding output for a specific logic gate.
• Binary Operations: This term points to operations where binary numbers 0 and 1 are used.
• High and Low Logic Levels: In digital systems, a “high” level usually signifies a binary ‘1’ and is linked with a voltage nearing the system’s supply voltage. Conversely, a “low” level is associated with a binary ‘0’ and a voltage close to zero or ground.
• Combination Circuits: These are circuits where the resulting output is a function of its current inputs.
• Series Logic: This describes circuits where the resulting output isn’t just determined by its present inputs and past input values. Elements that store information, such as flip-flops, fall under this category.

7 Types of Logic Gates are:

1. AND
2. OR
3. NOT
4. NOR
5. NAND
6. XOR
7. XNOR

Let us understand each of these in detail :

1. AND Gate

The AND gate is one of the fundamental logic gates in digital electronics. It operates based on the logical AND operation. For a 2-input AND gate, the Boolean expression can be written as Z=A⋅B, where Y is the output.

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Must Read – What is Universal Logic Gate?

2. OR Gate

An OR gate has a single output and two or more inputs. When at least one of the inputs is 1, the output of this gate is 1. The OR gate’s Boolean logic is Z=A+B for inputs A and B.

Truth Table :

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3. NOT Gate

A NOT gate has a single output and only one input. The output is the inverse of the input & is also called the inverter. The NOT gate’s Boolean logic is Z= ~A for an input A.

Truth Table :

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4. NOR Gate

A NOR gate has a single output and two or more inputs. The output is 1 only when all of the inputs are 0. For all other combinations, the output is 0. The NOR gate’s Boolean logic is Z= ~ (A+B)​ for inputs A and B.

Truth Table:

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5. NAND Gate

A NAND gate has a single output and two or more inputs. The output is 0 only when all of the inputs are 1. For all other combinations, the output is 1. The NAND gate’s Boolean logic is Z= ~ (A.B) for inputs A and B.

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6. XOR Gate

An XOR gate has a single output and two or more inputs & is called exclusive OR. The output is 1 only when an odd number of inputs are 1. The XOR gate’s Boolean logic for inputs A and B is Z=A⊕B = ~A.B+A.~B.

Truth Table:

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7. XNOR Gate

An XNOR gate has a single output and two or more inputs & is called exclusive NOR. The output is 1 only when an even number of inputs are 1. The XNOR gate’s Boolean logic for inputs A and B is Z= ~ (A⊕B) = A.B+ ~A. ~B

Truth Table:

Symbol :

Logic gates form the foundation of digital electronics and digital systems. Comprising basic units like AND, OR, NOT, NAND, NOR, XOR, and XNOR, these gates enable the execution of logical operations on binary data. Their simple binary input-output relationships can be represented using truth tables, and their behaviour can be defined using Boolean algebra. Keep learning, keep exploring!