Logic Gate

Definition

A logic gate is a device that performs a fundamental Boolean logic function such as NOT, AND, OR, NAND, NOR, XOR, etc. From binary inputs, a logic gate returns a binary output of 1 (true) or 0 (false).

Types of Logic Gates

• NOT – A NOT gate only has one input, and the gate inverses the logic. The output is NOT the input. An input of logical 1 produces an output of logical 0, and an input of logical 0 produces an output of logical 1.

Below is a list of other common logic gates and the function they perform on a two-input digital circuit.

• AND – Output is true if input A AND input B are true. Outputs a logical 1 only if both inputs are logical 1. All other inputs produce an output of logical 0.
  
  

  A	B	AND
  0	0	0
  0	1	0
  1	0	0
  1	1	1
  AND gate truth table.

• OR – Output is true if input A OR input B is true. Outputs a logical 1 if either input is logical 1, and only outputs a logical 0 if both inputs are logical 0.
  
  

  A	B	OR
  0	0	0
  0	1	1
  1	0	1
  1	1	1
  OR gate truth table.

• NAND – Abbreviation for “NOT AND.” Performs the AND function, followed by the NOT function to produce the logical inverse of an AND gate. Outputs a logical 0 only if both inputs are logical 1. All other inputs produce an output of logical 1.
  
  

  A	B	NAND
  0	0	1
  0	1	1
  1	0	1
  1	1	0
  NAND gate truth table.

• NOR – Abbreviation for “NOT OR.” Performs the OR function, followed by the NOT function to produce the logical inverse of an OR gate. Outputs a logical 0 if either input is logical 1, and only outputs a logical 1 if both inputs are logical 0.
  
  

  A	B	NOR
  0	0	1
  0	1	0
  1	0	0
  1	1	0
  NOR gate truth table.

• XOR – Abbreviation for “Exclusively-OR.” Output is true if EXCLUSIVELY input A is true OR if EXCLUSIVELY input B is true. Outputs a logical 1 if the two input values differ, and outputs a logical 0 if the inputs are the same.
  
  

  A	B	XOR
  0	0	0
  0	1	1
  1	0	1
  1	1	0
  XOR gate truth table.

Keywords