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Johnson–Nyquist noise
Johnson–Nyquist noise (thermal noise, Johnson noise, or Nyquist noise) is the electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage. The generic, statistical physical derivation of this noise is called the fluctuation-dissipation theorem, where generalized impedance or generalized susceptibility is used to characterize the medium.
Thermal noise in an ideal resistor is approximately white, meaning that the power spectral density is nearly constant throughout the frequency spectrum (however see the section below on extremely high frequencies). When limited to a finite bandwidth, thermal noise has a nearly Gaussian amplitude distribution.
== History ==
This type of noise was first measured by John B. Johnson at Bell Labs in 1926.〔("Proceedings of the American Physical Society: Minutes of the Philadelphia Meeting December 28, 29, 30, 1926" ), Phys. Rev. 29, pp. 367-368 (1927) – a February 1927 publication of an abstract for a paper - entitled "Thermal agitation of electricity in conductors" - presented by Johnson during the December 1926 APS Annual Meeting〕〔J. Johnson, ("Thermal Agitation of Electricity in Conductors" ), Phys. Rev. 32, 97 (1928) – details of the experiment〕 He described his findings to Harry Nyquist, also at Bell Labs, who was able to explain the results.〔H. Nyquist, ("Thermal Agitation of Electric Charge in Conductors" ), Phys. Rev. 32, 110 (1928) – the theory〕
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