NOT Logic Gate

A NOT logic gate takes only a single binary input and produces the output. It inverts or reverses the input that’s why it is also called an inverter.

• If the input is 1(HIGH), then the output will be 0 (LOW)
• If the input is 0(LOW), then the output will be 1 (HIGH)

It is different from OR and AND gates, because they take two binary inputs.

NOT Gate Symbol

NOT logic gate symbol looks like a triangle with a small circle, called a bubble, at the output. The following diagram shows the NOT gate symbol

Truth Table of NOT Gate

The input for the NOT gate is only one, so the NOT gate contains 2¹ = 2 possible input combinations. Where the input can either be 0 or 1. The following is the Truth Table for NOT gate, which shows the output, which is the reverse of its input.

Boolean Expression of NOT Gate

The following diagram shows the Boolean expression for the NOT gate, where the bar represents the NOT operation. Some other notations can also be used instead of the bar for the NOT gate.

 

NOT Gate Combined with Other Logic Gates

NOT gate reverses the output of another logic gate. When NOT logic gate is connected with the output of another logic gate, it produces the reverse of that gate’s output. The following Table expleain it

Combination	Resulting Gate	Basic Definition
OR + NOT	NOR	Output of OR gate is reversed
AND + NOT	NAND	Output of AND gate is reversed
XOR + NOT	XNOR	Output of XOR gate is reversed
XNOR + NOT	XOR	Output of OR gate is reversed
NAND + NOT	AND	NOT reverses the NAND output and produces AND.
NOR + NOT	OR	NOT reverses the NOR output and produces OR.

1. OR Gate + NOT Gate = NOR Gate

The OR gate first produces its output, and the NOT gate reverses it.

Y = (A + B)̅

So, the output of NOR is the opposite of the OR gate.

2. AND Gate + NOT Gate = NAND Gate

The AND gate produces its output, and the NOT gate reverses it.

Y = (A · B)̅

So, the output of NAND is the opposite of the AND gate.

3. XOR Gate + NOT Gate = XNOR Gate

The NOT gate reverses the output of the XOR gate.

Y = (A ⊕ B)̅

Therefore, XOR + NOT = XNOR.

4. XNOR Gate + NOT Gate = XOR Gate

The NOT gate reverses the output of the XNOR gate.

Y = (A ⊙ B)̅

Therefore, XNOR + NOT = XOR.

5. NAND Gate + NOT Gate = AND Gate

When a NOT gate is connected to the output of a NAND gate, it reverses the NAND output.

Y = ((A · B)̅)̅ = A · B

Therefore, NAND + NOT = AND.

6. NOR Gate + NOT Gate = OR Gate

When a NOT gate is connected to the output of a NOR gate, it reverses the NOR output.

Y = ((A + B)̅)̅ = A + B

Therefore, NOR + NOT = OR.

Yes. If you want implementation of a NOT gate using all other basic gates, there are 6 implementations because the other six gates are AND, OR, NAND, NOR, XOR, and XNOR.

Implementation of NOT Gate Using Other Logic Gates

1. NOT Gate Using AND Gate

A NOT gate can be implemented using an AND gate by fixing one input of the AND gate to 0.

For inputs A and 0:

Y = A · 0 = 0

This does not produce NOT A, so a simple AND gate alone cannot implement a NOT gate with a fixed input.

Therefore, AND gate alone cannot be used to implement NOT.

2. NOT Gate Using OR Gate

Similarly, an OR gate alone cannot implement NOT A by fixing one input to a constant.

For example:

Y = A + 0 = A

This gives A, not A̅.

Therefore, OR gate alone cannot implement NOT.

3. NOT Gate Using NAND Gate

A NAND gate can easily be used as a NOT gate by connecting both inputs together.

Y = (A · A)̅

Since:

A · A = A

Therefore:

Y = A̅

So, one NAND gate is sufficient to implement a NOT gate.

4. NOT Gate Using NOR Gate

A NOR gate can also be used as a NOT gate by connecting both inputs together.

Y = (A + A)̅

Since:

A + A = A

Therefore:

Y = A̅

So, one NOR gate is sufficient to implement a NOT gate.

5. NOT Gate Using XOR Gate

An XOR gate can be used to implement a NOT gate by connecting one input to 1.

Y = A ⊕ 1

An XOR gate produces 1 when its inputs are different. Therefore:

• A = 0 → Y = 1
• A = 1 → Y = 0

Thus:

Y = A̅

6. NOT Gate Using XNOR Gate

An XNOR gate can be used to implement a NOT gate by connecting one input to 0.

Y = A ⊙ 0

XNOR produces 1 when its inputs are the same. Therefore:

• A = 0 → Y = 0
• A = 1 → Y = 1

Wait—this gives Y = A, not A̅.

To implement NOT using XNOR, connect one input to 1:

Y = A ⊙ 1 = A̅

Therefore, an XNOR gate with one input connected to 1 implements a NOT gate.

Summary

Gate Used	Connection	NOT Implementation
AND	Cannot with AND alone	❌
OR	Cannot with OR alone	❌
NAND	Both inputs connected to A	✅
NOR	Both inputs connected to A	✅
XOR	One input = 1	✅
XNOR	One input = 1	✅

 

NOT Gate Using Transistor

A NOT gate can also be built using a transistor-based circuit. In a simple transistor inverter, the transistor changes its output state according to the input signal.

When the input is LOW, the transistor remains OFF and the output is HIGH. When the input is HIGH, the transistor turns ON and the output becomes LOW.

Thus, the circuit produces the opposite of the input, which is the basic operation of a NOT gate.

NOT Gate Using Circuit Switch

 

Applications of NOT Gate

NOT gates are widely used in digital electronic circuits. Common applications include:

• Signal inversion: Converts a HIGH signal into LOW and vice versa.
• Control circuits: Produces an opposite control signal when required.
• Digital systems: Used to create more complex logic functions.
• Memory circuits: Used as part of different digital storage circuits.
• Computing circuits: Helps implement logical and arithmetic operations.
• Logic gate implementation: Used when an inverted signal is required.

NOT Gate vs Other Logic Gates

Logic Gate	Number of Inputs	Basic Operation
NOT	1	Inverts the input
AND	2 or more	Output is 1 when all inputs are 1
OR	2 or more	Output is 1 when at least one input is 1
NAND	2 or more	Inverted AND operation
NOR	2 or more	Inverted OR operation
XOR	2 or more	Output is 1 when inputs are different
XNOR	2 or more	Output is 1 when inputs are the same