Logic Gates

Logic Gates Basics

  • Logic Gates are the basic building blocks of any digital system.
  • They are primarily designed to perform logical operations on one or more logical inputs and produce a single logical output.
  • The common types of logic gates are: AND, OR, NOT, NAND, NOR, XOR, XNOR.

AND Gate

  • An AND gate produces a high output (1) only if all its inputs are high.
  • If any of the inputs is low (0), the output is low.

OR Gate

  • An OR gate produces a high output (1) if any or all of its inputs are high.
  • The output is low only when all inputs are low.

NOT Gate

  • A NOT gate, also known as an inverter, produces the inverted version of the input at its output.
  • That is, a high (1) input results in a low (0) output and vice versa.

NAND Gate

  • A NAND gate operates as an AND gate followed by a NOT gate.
  • It produces a low output only if all its inputs are high.
  • Otherwise, the output is high.

NOR Gate

  • A NOR gate operates as an OR gate followed by a NOT gate.
  • It produces a high output only when all its inputs are low.
  • If any input is high, the output is low.

XOR Gate

  • An XOR (exclusive OR) gate produces a high output if the number of high inputs is odd.
  • With two inputs, it produces a high output if exactly one input is high.

XNOR Gate

  • An XNOR (exclusive NOR) gate operates as the complement of XOR gate.
  • It produces a high output if the number of high inputs is even.
  • With two inputs, it produces a high output if both inputs are same.

Truth Tables

  • The relationship between the input and the output of a logic gate can be expressed in the form of a table called a truth table.
  • A truth table lists all possible combinations of input values and the corresponding output value.

Logic Gate Symbols

  • Each logic gate has a distinctive graphical symbol used in circuit diagrams to denote its operation.
  • Understanding and interpreting these symbols is crucial for digital circuit design.

Combination of Logic Gates

  • Logic gates can be combined or sequenced to form a composite gate or complex logic circuits, allowing complex operations to be performed.
  • These combinations can be expressed and simplified using Boolean algebra or Karnaugh maps.

Practical Applications

  • Logic gates form the foundation of digital circuits like counters, registers, memory units and microprocessors.
  • They are also used in devices such as calculators, television and radio equipment, digital computers, etc.