Basic Logic Gates

By Aina Parasher|Updated : August 26th, 2022

A logic gate is an electronic circuit that can make decisions in accordance with the set of values present at its input. There are only 3 basic logic gates namely AND, OR, and NOT, but we can create very complex systems with the interconnection of these gates. The interconnection of these gates to perform various logical operations is called logic design. Inputs and outputs of basic logic gates can occur in two levels: HIGH and LOW or, ON and OFF or, LOGIC 1 and LOGIC 0 or, TRUE and FALSE. A table that represents all possible combinations of inputs and their corresponding outputs is called a "truth table".

As we discussed earlier there are 3 basic logic gates but in practice along with these basic logic gates, we do use other logic gates derived from these three. They are the NAND gate, NOR gate, EX-OR gate, EX-NOR, and the Buffer gate. In fact, the NAND and NOR gates are known as universal gates as we can implement any logic gate including the basic logic gates in an easier and more economical way on an IC chip.

What are the Basic Logic Gates?

The basic logic gates are the building blocks of the digital circuit, they are the AND gate, OR gate, and the NOT gate. We can derive the other logic gates from the interconnection of these three basic logic gates.

In this article, we will discuss the basic logic gates. The basic logic gates are given below.

  • AND
  • OR
  • NOT

Along with these basic logic gates, we will also discuss the other logic gates namely-

  • NAND gate
  • NOR gate
  • EX-OR gate
  • EX-NOR gate
  • Transfer (or) Buffer gate

Basic Logic Gates - AND Gate

An AND gate has two or more inputs but only one output. In this logic gate, the output is logic 1 when all its inputs are set to 1 or HIGH. The Output is logic 0 when one of the inputs is set to 0 or LOW. For the sake of understanding, I have given the two-input AND gate logic symbol and its truth table.

and

AND TT

Basic Logic Gates - OR Gate

An OR gate may have two or more inputs as per the need of the application, but it has only one output just like AND gate. In this logic gate, the output is logic 1 when at least one of its inputs is set to 1 or HIGH. In this logic gate output is logic 0 when all the inputs are set to 0 or LOW.

or

or tt

Basic Logic Gates - NOT Gate

This logic gate is also known as an inverter gate or compliment gate as the output of this device is the complement of its input. This logic gate has only one input and one output. If the input is set to 0 or LOW, then the output must be 1 or HIGH. In the same way, it complements the input 1 to 0.

not

not tt

NAND Gate

In general NAND logic gate is a type of universal gate that means NOT AND, i.e., it is the complement of the basic AND gate. Just like the AND gate, this logic gate can have multiple inputs but only one output will be present. For this logic gate, the output is logic 1, when one of its inputs is set to 0 or LOW. The output is logic 0 when all its inputs are set to 1 or HIGH.

nand

nand tt

NOR Gate

The NOR gate is the complement of the basic OR gate. Just like the OR gate, it’s also a multi-input single-output logic gate. The output is logic 1 when all its inputs are set to 0 or LOW. The output is logic 0 when at least one of its inputs is set to 1 or HIGH. It is a type of universal gate.

nor

nor tt

EX-OR Gate

An EX-OR gate is a two-input single-output logic gate. The output is logic 1 when only one of the two inputs is set to 1 or HIGH. The output is logic 0 when both the inputs are the same i.e., either both inputs are set to 1 or both inputs are set to zero.

  • Due to this property, this logic gate can be used as an inequality detector.
  • The expression for this logic gate is

exor exp

exor

exor tt

EX-NOR Gate

This is also a two-input single-output logic gate, which is a complement to the EX-OR gate. The output is logic 1 when either both inputs are set to 1 or both inputs are set to 0. The output is logic 0 when only one of the two inputs is set to 1 or HIGH. 

  • The EX-NOR gate can be used as an equality detector as its output logic 1 when both the inputs are the same.
  • The expression for its output is

exnor exp

exnorexnor tt

Transfer (or) Buffer Gate

The buffer logic gate just transfers the input, but it does not perform any logical operation. The binary value of the output is the same as the binary value of the input. This circuit is used for the power amplification of the signal in electronic devices. It is equivalent to two inverters connected in a cascade.

buffer

buffer tt

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FAQs on Basic Logic Gates

  • The AND, OR, and NAND gates are known as basic logic gates because every other logic gate we are using in the digital circuits is a subsidiary of these three gates.

  • The logic gates NAND and the NOR are having the reputation of universal gates as we can recognize the function of any logic gate by using these two logic gates. In practice, it is economical and easier to fabricate the other logic gates on the IC chip using NAND and NOR gates.

  • The binary output of the buffer gate is the same as that of the input as it does not perform any logical operation, but this circuit will be used for the power amplification of the signal in electronic devices.

  • An EX-OR gate is known as an anti-coincidence logic gate or inequality detector due to its property of identification of two different inputs. In this logic gate, the output is logic 1, when only one of the two inputs is set to 1 or HIGH. The output is logic 0 when both the inputs are the same i.e., either both inputs are set to 1 or both inputs are set to zero. 

  • The interconnection of logic gates to perform various logical operations is called logic design. A logic gate is an electronic circuit that can make decisions in accordance with the set of values present at its input. 

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