Electronic noise 3966982 226174966 2008-07-17T04:20:44Z 119.95.138.191 /* Burst noise */ {{Merge|signal noise|date=May 2008}} {{Merge|noise level|date=May 2008}} {{Expand|date=January 2007}} '''Electronic noise''' is an unwanted signal characteristic of all [[electronics|electronic]] [[electrical circuit|circuits]]. Depending on the circuit, the [[noise (physics)|noise]] put out by electronic devices can vary greatly. This noise comes from many different electronic effects. Thermal noise and shot noise are inherent to all devices. The other types depend mostly on manufacturing quality and semiconductor defects. In some applications, electronic noise can serve a useful purpose. A common example of this is in [[random number generation]]. == Types == === Shot noise === {{main|Shot noise}} Shot noise in electronic devices consists of random fluctuations of the [[electric current]] in an electrical [[Conductor (material)|conductor]], which are caused by the fact that the current is carried by discrete charges ([[electron]]s). === Thermal noise === {{main|Johnson-Nyquist noise}} Johnson-Nyquist noise (sometimes '''thermal noise''', '''Johnson noise''' or '''Nyquist noise''') is the [[noise (physics)|noise]] generated by the [[Dynamic equilibrium|equilibrium]] fluctuations of the [[electric current]] inside an [[electrical conductor]], which happens regardless of any applied [[voltage]], due to the random thermal motion of the charge carriers (the [[electron]]s). The charges may be bound (for a dielectric material) or free (for a conductor). Free charges generate kinetic energy from their motion according to the equation E=(mv<sup>2</sup>)/2. This kinetic energy results in noise. Bound charges generate kinetic energy when the direction of polarity changes. This noise is characterized as [[Additive white Gaussian noise]] (AWGN) with a [[noise spectral density]] in Watt/Herz of ''N''<sub>o</sub> = ''kT'', where ''k'' is [[Boltzmann's constant]] in joules per [[kelvin]], and ''T'' is the receiver [[system]] [[noise temperature]] in kelvin. Since thermal noise can be considered as [[white noise]], the total noise power ''N'' detected in a receiver with bandwidth ''B'' is ''BN''<sub>o</sub>. This phenomenon limits the minimum [[signal level]] that any [[Receiver (radio)|radio receiver]] can usefully respond to, because there will always be a small but significant amount of [[Johnson-Nyquist noise|thermal noise]] arising in its input circuits. This is why [[radio telescope]]s, which search for very low levels of signal from [[star]]s, use [[front-end and back-end|front-end]] circuits, usually mounted on the [[parabolic reflector|aerial dish]], cooled in [[liquid nitrogen]] to a very low temperature. === Flicker noise === {{main|Flicker noise}} Flicker noise, also known as '''1/''f'' noise''', is a signal or process with a [[frequency spectrum]] that falls off steadily into the higher frequencies, with a [[pink noise|pink]] spectrum. It occurs in almost all electronic devices, and results from a variety of effects, though always related to a direct current. === Burst noise === {{main|Burst noise}} Burst noise consists of sudden step-like transitions between two or more levels (non-[[Gaussian]]), as high as several hundred [[millivolt]]s, at random and unpredictable times. Each shift in offset voltage or current lasts for several milliseconds, and the intervals between pulses tend to be in the [[audio]] range (less than 100 [[hertz|Hz]]), leading to the term '''popcorn noise''' for the popping or crackling sounds it produces in audio circuits. ang saya === Avalanche noise === See [[Avalanche diode]] and [[Avalanche breakdown]]. === Lightning === Lightning is a natural phenomenon that consists of large currents that cause fluctuations that may result in noise in a system. == Measurement == Electronic noise is properly measured in [[watt]]s of [[Electric power|power]]. Because noise is a random process, it can be characterized by [[Stochastic process|stochastic]] properties such as its [[variance]], [[Probability distribution|distribution]], and [[spectral density]]. The spectral distribution of noise can vary by [[frequency]], hence its power density is measured in watts per hertz <math>\left( \frac\mathrm{W}\mathrm{Hz}\right)</math>. Since the real power in a [[resistor|resistive]] element is proportional to the square of the [[voltage]] across the element, noise voltage (density) can be described by taking the square root of the noise power density, resulting in volts per root hertz <math>\left( \frac\mathrm{V}{\sqrt\mathrm{Hz}}\right)</math>. [[Integrated circuit]] devices, such as [[operational amplifier|op-amps]] commonly quote [[equivalent input noise]] level in these terms (at room temperature). == See also == *[[Noise]] *[[Generation-recombination noise]] *[[Interference (communication)]] *[[Phase noise]] ==References== {{Nofootnotes|date=March 2008}} {{reflist}} *[http://www.sengpielaudio.com/calculator-noise.htm White noise calculator, thermal noise - Voltage in microvolts, conversion to noise level in dBu and dBV and vice versa] ==Further reading== *{{cite journal | last = Constable, J. H. | first = | authorlink = | coauthors = | title = Investigation of Environmental Noise in Small Electrical Conductors | journal = IEEE Transactions on Instrumentation and Measurement | volume = 55 | issue = 6 | pages = 2045–2054 | publisher = IEEE | date = December 2006 | url = http://ieeexplore.ieee.org/xpls/abs_all.jsp?isnumber=4014679&arnumber=4014691&count=64&index=23 | doi = 10.1109/TIM.2006.884117 | id = | accessdate = }} *{{cite journal | last = G. Gomila and L. Reggiani | first = | authorlink = | coauthors = | title = Anomalous crossover between thermal and shot noise in macroscopic diffusive conductors | journal = Physical Review B | volume = 62 | issue = 12 | pages = 8068–8071 | publisher = APS |date=September 2000 | url = http://prola.aps.org/abstract/PRB/v62/i12/p8068_1 | doi = 10.1103/PhysRevB.62.8068 | id = | accessdate = | format = subscription required }} * {{cite book | author=Sh. Kogan| title=Electronic Noise and Fluctuations in Solids | publisher=Cambridge University Press | year=1996 | id=ISBN 0521460344}} * {{cite book | author=M. V. Kunnavakkam| title=Experimental investigation of current dependent noise in metal wires (M.S. Thesis) | publisher=Binghamton University | year=1996 | id=}} [[Category:Electronics terms]] [[Category:Noise]] [[he:רעש (פיזיקה)]] [[it:Rumore (elettronica)]] [[es:Ruido (comunicación)]]