Noise or Electrical Noise is any unwanted electrical signal interferes or distorts the information signal.

It affects the signal inside or outside the equipment and generates error. It affects both analog and digital signal and quality of information signal at receiving end.It can enters via communication equipment or transmission medium.Noise can not be eliminated completely.

Types of Noise

We can divide noise into two types based on the presence of information signal.

  • Uncorrelated Noise.
  • Correlated Noise.

Uncorrelated Noise

It is present always regardless of information signal is present or not.Further divided into two types,

  1. Internal Noise
  2. External Noise

Internal Noise

This kind of noise is generated within the device. sources are components used in circuits while functioning.Further divided into following

  • Shot Noise: Random movement of electron in semiconductor components ,due to different barriers / junctions, generates variation in current.This variation is shot noise.
  • Transit time Noise: Transit time is the time in which carriers (hole or electron) travel the distance from input to the output of the circuit.At low frequency it is negligible.Transit-time noise results when a signal frequency’s period is the same as the time an electron takes to travel from sender to receiver.
  • Thermal Noise: It is also known as white noise and Johnson noise. It is due to the internal resistance of the component. Its intensity increases with the increase in number of components.It is due to the random motion of electron in a conductor due to thermal agitation.

External Noise

Noise generated outside the device or system.Divided into following

  • Atmospheric Noise: Natural noise,produced within earth atmosphere. It is due to the natural electrical conditions such as lightning.
  • Extraterrestrial Noise. Due to outside of earth atmosphere. known as deep space noise.Its sources are milky ways, Galaxies, sun and etc.
  • Solar Noise: directly generated from sun’s heat.
  • Cosmic Noise: Generates from galaxies and other bodies. Intensity is low due to long distance.
  • Man-made Noise / Industrial Noise: Artificially made by man.Electrical motors, switching equipment, automobile ignition system. Its intensity is high in populated areas.

Correlated Noise

It is present only if the information signal is present. There are two types.

  • Harmonic Distortion.It is due to the unwanted harmonics of a signal. 1st is the fundamental, 2nd, 3rd,4th….. are the noises.
  • Intermodulation Distortion. Produced when two signals are sum during the process of modulation. It is the cross product of modulating and carrier frequencies.


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