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Logic Gates




Logic Gates

  • A logic gate is an digital circuit which follows logical relationship between input and output voltages
  • It has one output and one or more inputs
  • They are the basic building blocks from which most of the digital systems are build up
  • They are called logic gates as they control the flow of information

  • The five common logic gates used are NOT, AND, OR, NAND, NOR.
  • Each logic gate is indicated by a symbol and its function is defined by a truth table that shows all the possible input logic level combinations with their respective output logic levels.
  • Truth tables help understand the behaviour of logic gates.

AND gate

  • This gates has two or more input and one output. The output Y of AND gate is 1 only when both the input A and B are 1.
  • Here is the logical symbol of AND gate
    Logic Gates
  • Truth Table is given below as

NOT gate

  • This gates has one input and one output. This is most simplest gate. It produces a '1' output if the input is '0' and vice-versa.
  • It is also called inverter
  • Here is the logical symbol of NOT gate

  • Truth Table is given below as



OR gate

  • This gates has two or more input and one output. The output Y of OR gate is 1 when either input A or input B or both are 1s
  • Here is the logical symbol of OR gate

  • Truth Table is given below as

NAND gate

  • This is AND gate followed by NOT gate. If inputs A and B are both '1', the output Y is not '1'.
  • The gate gets its name from this NOT AND behaviour
  • This is also called universal gate as all other gates can be created from it

  • Truth Table is given below as

NOR gate

  • This is OR gate followed by NOT gate. Its output Y is '1' only when both inputs A and B are '0'
  • The gate gets its name from this NOT OR behaviour
  • This is also called universal gate as all other gates can be created from it

  • Truth Table is given below as

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