Digital engineering

NOT Gate: Symbol Working Principle Truth Table & Circuit Diagram


The digital logic NOT gate is one of the basic type of digital logic gates that referred to as an Inverter or simply an Inverting Buffer. A inverting NOT gate is a single output and input. When the single input of NOT is “1” the output will be compliment of “1” i.e. “0”. If input is “LOW” than output will be “HIGH”. The Boolean expression of the NOT are Y =Ā.

What is a NOT Gate?

A NOT gate is an inverter circuit. It inverts the digital input signal. Conversely, a logical NOT gate always become low (logical 0) output when the input signal is HIGH (logical 1). If the input is A than output will be Ā. Here the compliment symbol is Y =Ā. Let us understand with example, if the input is “0” than output is “1”. The input is “1” the input is “0”.

Symbol of NOT gate

This logic consist only one input and one output terminal. It has bobble on the head of triangle which shows the inverts the output. The Boolean expression of digital logic NOT: Y =Ā. Here bar (-) shows the inverting of input.


Logic NOT Gate Truth Table

Symbol Truth Table


Inverter or NOT

0 1
1 0
Boolean Expression is Q = Ā Read as inverse of A gives Q


Logic NOT has property to invert the input terminal. If the input single is “HIGH” the output will “LOW” and vice versa. This gate is not use for decision making like wise AND or OR gates in which has two terminal input. The NOT is also available in IC’s in 4 or 6 pin.

Other digital logic gates are: AND gates, OR gates, NAND gates, NOR gates, XOR gates and XNOR gates. 

NOT Gate Transistor Circuit Diagram

NOT is also design with a transistor. The circuit diagram of NOT with transistor is given below:


Working of NOT Gate

Let us understand the working of NOT gate with transistor circuit with high input i.e. +5V. When applied +5v at base terminal, transistor start conduction. The Vcc voltage of transistor will get a path to the earth through resistor R. At ON stage the transistor is behaves like a short circuit and all voltage drop across resistance R and now voltage appear at X the output (X) and hence the output of the inverter is be zero.


In practically there will be some voltage drop across the collector emitter voltage in ON condition i.e. 0.6v this is much low as compare with 5volt so we neglect the 0.6v across the collector emitter voltage.

Now understand the behavior of transistor when in base (A) voltage is “0” or grounded.

The transistor behaves like an “OFF” circuit because there is no base current and the power supply of transistor is not a grounded path. So, entire voltage appears across the output terminal.

Signal Inversion using Active-low input Bubble

The bubble present on the head of NOT is the meaning of inversion of input signal. But this bubble is also present on input of gates to shows an active low input. The input inversion in not only use in NOT, it is also using in any digital logic gate. Basic meaning of bubble in logic gates is the inversion of input signal.


NAND and NOR Gate Equivalents

The NOT gates or inverter can also use in construction of NAND and NOR gates by short the input terminal or connecting together ALL their inputs to a common input signal


Commonly available logic NOT gate or Inverter IC’s include:

TTL Logic NOT Gates

  • 74LS04 → Hex Inverting NOT
  • 74LS14 → Hex Schmitt Inverting NOT
  • 74LS1004 → Hex Inverting Drivers

CMOS Logic NOT Gates

  • CD4009 → Hex Inverting NOT
  • CD4069 → Hex Inverting NOT

7404 NOT Gate IC or Inverter

The IC 7404 is the NOT which is commercially available in market. In this IC package the number of transistor is six or simply six NOT gate.


People also ask about NOT gate

What a NOT gate does?

A NOT perform the inverse operation of input signal. In other word, if input is “ZERO”, then the output will be “ONE”. Similarly, if input is “ONE”, than output will be “ZERO”. This means it performs logical negation on its input.

What is NOT NOT gate?

A NOT is a digital logic gates. It consist only one input and output terminal. Logically with NOT gates, the input and the output swap, that means input is zero the output is one or input is one output will be zero. It negates the values of data or signal in its input.

What is NOT gate also called?

This gate performs inverse operation. So, it is called inverter circuit.

What is the equation of NOT?

NOT is also known as inverter circuit. If the input is “A” than output will be “Ā”. The “Ā”. It performs inverse or complement of the input giving. The Boolean Expression is: A = Ā (NOT A).

What is meant by NOR gate?

The NOR gate is one of the type of digital logic circuit that perform compliment operation of OR gates. Signal. If both input is HIGH than output is low. And if any one of the inputs is high than output is LOW. NOR is the inverses of the OR operator.

Is NOR a universal gate?

A universal gates is that gate which is use to perform implement any Boolean function need to use any other gates type. The universal gates are NAND and NOR.

Who invented the NOT gate?

Mathematician George Boole invented the NOT which is died 150 years ago.

WHY IS NOT gate called an inverter?

The NOT performs compliment or inverse operation. So, it is called inverter.

What is the Boolean expression for a NOT gate?

The Boolean Expression of digital logic NOT is: A = Ā (NOT A).

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