the amplitude level of the undesired background noise (同)background level
talk frankly with; lay it on the line; "I have to level with you"
become level or even; "The ground levelled off" (同)level off
indicator that establishes the horizontal when a bubble is centered in a tube of liquid (同)spirit_level
height above ground; "the water reached ankle level"; "the pictures were at the same level"
an abstract place usually conceived as having depth; "a good actor communicates on several levels"; "a simile has at least two layers of meaning"; "the mind functions on many strata simultaneously" (同)layer, stratum
tear down so as to make flat with the ground; "The building was levelled" (同)raze, rase, dismantle, tear down, take_down, pull down
not showing abrupt variations; "spoke in a level voice"; "she gave him a level look"- Louis Auchincloss (同)unwavering
aim at; "level criticism or charges at somebody"
being on a precise horizontal plane; "a billiard table must be level"
oriented at right angles to the plumb; "the picture is level"
incomprehensibility resulting from irrelevant information or meaningless facts or remarks; "all the noise in his speech concealed the fact that he didnt have anything to say"
the auditory experience of sound that lacks musical quality; sound that is a disagreeable auditory experience; "modern music is just noise to me" (同)dissonance, racket
a loud outcry of protest or complaint; "the announcement of the election recount caused a lot of noise"; "whatever it was he didnt like it and he was going to let them know by making as loud a noise as he could"
sound of any kind (especially unintelligible or dissonant sound); "he enjoyed the street noises"; "they heard indistinct noises of people talking"; "during the firework display that ended the gala the noise reached 98 decibels"
This article is about fundamental noise processes in electronics. For electronic noise arising from outside sources, see electromagnetic compatibility and electromagnetic interference. For acoustic noise due to electromagnetic fields, see electromagnetically excited acoustic noise and vibration. For other uses, see Noise (disambiguation).
Analog display of random fluctuations in voltage in pink noise.
In electronics, noise is an unwanted disturbance in an electrical signal.[1]:5 Noise generated by electronic devices varies greatly as it is produced by several different effects.
In communication systems, noise is an error or undesired random disturbance of a useful information signal. The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources. Noise is, however, typically distinguished from interference,[a] for example in the signal-to-noise ratio (SNR), signal-to-interference ratio (SIR) and signal-to-noise plus interference ratio (SNIR) measures. Noise is also typically distinguished from distortion, which is an unwanted systematic alteration of the signal waveform by the communication equipment, for example in signal-to-noise and distortion ratio (SINAD) and total harmonic distortion plus noise (THD+N) measures.
While noise is generally unwanted, it can serve a useful purpose in some applications, such as random number generation or dither.
Contents
1Noise types
1.1Thermal noise
1.2Shot noise
1.3Flicker noise
1.4Burst noise
1.5Transit-time noise
2Coupled noise
2.1Sources
2.2Mitigation
3Quantification
4Dither
5See also
6Notes
7References
8Further reading
9External links
Noise types
Different types of noise are generated by different devices and different processes. Thermal noise is unavoidable at non-zero temperature (see fluctuation-dissipation theorem), while other types depend mostly on device type (such as shot noise,[1][2] which needs a steep potential barrier) or manufacturing quality and semiconductor defects, such as conductance fluctuations, including 1/f noise.
Thermal noise
Main article: Johnson–Nyquist noise
Johnson–Nyquist noise[1] (sometimes thermal, Johnson or Nyquist noise) is unavoidable, and generated by the random thermal motion of charge carriers (usually electrons), inside an electrical conductor, which happens regardless of any applied voltage.
Thermal noise is approximately white, meaning that its power spectral density is nearly equal throughout the frequency spectrum. The amplitude of the signal has very nearly a Gaussian probability density function. A communication system affected by thermal noise is often modeled as an additive white Gaussian noise (AWGN) channel.
Shot noise
Main article: Shot noise
Shot noise in electronic devices results from unavoidable random statistical fluctuations of the electric current when the charge carriers (such as electrons) traverse a gap. If electrons flow across a barrier, such as that encountered in electrical contacts then they have discrete arrival times. Those discrete arrivals exhibit shot noise. Typically, the barrier in a diode is used.[3] Shot noise is similar to the noise created by rain falling on a tin roof. The flow of rain may be relatively constant, but the individual raindrops arrive discretely.
The root-mean-square value of the shot noise current in is given by the Schottky formula.
where I is the DC current, q is the charge of an electron, and ΔB is the bandwidth in hertz. The Schottky formula assumes independent arrivals.
Vacuum tubes exhibit shot noise because the electrons randomly leave the cathode and arrive at the anode (plate). A tube may not exhibit the full shot noise effect: the presence of a space charge tends to smooth out the arrival times (and thus reduce the randomness of the current).
Conductors and resistors typically do not exhibit shot noise because the electrons thermalize and move diffusively within the material; the electrons do not have discrete arrival times. Shot noise has been demonstrated in mesoscopic resistors when the size of the resistive element becomes shorter than the electron–phonon scattering length.[4]
Flicker noise
Main articles: Flicker noise and 1/f 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 spectrum. It occurs in almost all electronic devices and results from a variety of effects.
Burst noise
Main article: Burst noise
Burst noise consists of sudden step-like transitions between two or more discrete voltage or current levels, as high as several hundred microvolts, at random and unpredictable times. Each shift in offset voltage or current lasts for several milliseconds to seconds. It is also known a popcorn noise for the popping or crackling sounds it produces in audio circuits.
Transit-time noise
If the time taken by the electrons to travel from emitter to collector in a transistor becomes comparable to the period of the signal being amplified, that is, at frequencies above VHF and beyond, the transit-time effect takes place and noise input impedance of the transistor decreases. From the frequency at which this effect becomes significant, it increases with frequency and quickly dominates other sources of noise.[5]
Coupled noise
See also: Electromagnetic compatibility
While noise may be generated in the electronic circuit itself, additional noise energy can be coupled into a circuit from the external environment, by inductive coupling or capacitive coupling, or through the antenna of a radio receiver.
Sources
Intermodulation noise
Caused when signals of different frequencies share the same non-linear medium.
Crosstalk
Phenomenon in which a signal transmitted in one circuit or channel of a transmission systems creates undesired interference onto a signal in another channel.
Interference
Modification or disruption of a signal travelling along a medium
Atmospheric noise
This noise is also called static noise and it is the natural source of disturbance caused by lightning discharge in thunderstorm and the natural (electrical) disturbances occurring in nature.
Industrial noise
Sources such as automobiles, aircraft, ignition electric motors and switching gear, High voltage wires and fluorescent lamps cause industrial noise. These noises are produced by the discharge present in all these operations.
Solar noise
Noise that originates from the Sun is called solar noise. Under normal conditions there is constant radiation from the Sun due to its high temperature. Electrical disturbances such as corona discharges, as well as sunspots can produce additional noise. The intensity of solar noise varies over time in a solar cycle.
Cosmic noise
Distant stars generate noise called cosmic noise. While these stars are too far away to individually affect terrestrial communications systems, their large number leads to appreciable collective effects. Cosmic noise has been observed in a range from 8 MHz to 1.43 GHz, the latter frequency corresponding to the 21-cm hydrogen line. Apart from man-made noise, it is the strongest component over the range of about 20 to 120 MHz. Little cosmic noise below 20MHz penetrates the ionosphere, while its eventual disappearance at frequencies in excess of 1.5 GHz is probably governed by the mechanisms generating it and its absorption by hydrogen in interstellar space.[citation needed]
Mitigation
In many cases noise found on a signal in a circuit is unwanted. There are many different noise reduction techniques that can reduce the noise picked up by a circuit.
Faraday cage – A Faraday cage enclosing a circuit can be used to isolate the circuit from external noise sources. A faraday cage cannot address noise sources that originate in the circuit itself or those carried in on its inputs, including the power supply.
Capacitive coupling – Capacitive coupling allows an AC signal from one part of the circuit to be picked up in another part through interaction of electric fields. Where coupling is unintended, the effects can be addressed through improved circuit layout and grounding.
Ground loops – When grounding a circuit, it is important to avoid ground loops. Ground loops occur when there is a voltage difference between two ground connections. A good way to fix this is to bring all the ground wires to the same potential in a ground bus.
Shielding cables – A shielded cable can be thought of as a Faraday cage for wiring and can protect the wires from unwanted noise in a sensitive circuit. The shield must be grounded to be effective. Grounding the shield at only one end can avoid a ground loop on the shield.
Twisted pair wiring – Twisting wires in a circuit will reduce electromagnetic noise. Twisting the wires decreases the loop size in which a magnetic field can run through to produce a current between the wires. Small loops may exist between wires twisted together, but the magnetic field going through these loops induces a current flowing in opposite directions in alternate loops on each wire and so there is no net noise current.
Notch filters – Notch filters or band-rejection filters are useful for eliminating a specific noise frequency. For example, power lines within a building run at 50 or 60 Hz line frequency. A sensitive circuit will pick up this frequency as noise. A notch filter tuned to the line frequency can remove the noise.
Quantification
The noise level in an electronic system is typically measured as an electrical power N in watts or dBm, a root mean square (RMS) voltage (identical to the noise standard deviation) in volts, dBμV or a mean squared error (MSE) in volts squared. Noise may also be characterized by its probability distribution and noise spectral density N0(f) in watts per hertz.
A noise signal is typically considered as a linear addition to a useful information signal. Typical signal quality measures involving noise are signal-to-noise ratio (SNR or S/N), signal-to-quantization noise ratio (SQNR) in analog-to-digital conversion and compression, peak signal-to-noise ratio (PSNR) in image and video coding, Eb/N0 in digital transmission, carrier to noise ratio (CNR) before the detector in carrier-modulated systems, and noise figure in cascaded amplifiers.
Noise is a random process, characterized by stochastic properties such as its variance, distribution, and spectral density. The spectral distribution of noise can vary with frequency, so its power density is measured in watts per hertz (W/Hz). Since the power in a resistive element is proportional to the square of the voltage across it, noise voltage (density) can be described by taking the square root of the noise power density, resulting in volts per root hertz (). Integrated circuit devices, such as operational amplifiers commonly quote equivalent input noise level in these terms (at room temperature).
Noise power is measured in watts or decibels (dB) relative to a standard power, usually indicated by adding a suffix after dB. Examples of electrical noise-level measurement units are dBu, dBm0, dBrn, dBrnC, and dBrn(f1 − f2), dBrn(144-line).
Noise levels are usually viewed in opposition to signal levels and so are often seen as part of a signal-to-noise ratio (SNR). Telecommunication systems strive to increase the ratio of signal level to noise level in order to effectively transmit data. In practice, if the transmitted signal falls below the level of the noise (often designated as the noise floor) in the system, data can no longer be decoded at the receiver.[citation needed] Noise in telecommunication systems is a product of both internal and external sources to the system.
In a carrier-modulated passband analog communication system, a certain carrier-to-noise ratio (CNR) at the radio receiver input would result in a certain signal-to-noise ratio in the detected message signal. In a digital communications system, a certain Eb/N0 (normalized signal-to-noise ratio) would result in a certain bit error rate.
Dither
If the noise source is correlated with the signal, such as in the case of quantisation error, the intentional introduction of additional noise, called dither, can reduce overall noise in the bandwidth of interest. This technique allows retrieval of signals below the nominal detection threshold of an instrument. This is an example of stochastic resonance.
See also
Colors of noise
Generation–recombination noise
Phonon noise
Noise reduction and noise cancellation for audio and images
Matched filter for noise reduction in modems
Error correction for digital signals subject to noise.
Discovery of cosmic microwave background radiation
Notes
^e.g. cross-talk, deliberate jamming or other unwanted electromagnetic interference from specific transmitters
References
^ abcMotchenbacher, C. D.; Connelly, J. A. (1993). Low-noise electronic system design. Wiley Interscience. ISBN 0-471-57742-1.
^Kish, L. B.; Granqvist, C. G. (November 2000). "Noise in nanotechnology". Microelectronics Reliability. Elsevier. 40 (11): 1833–1837. doi:10.1016/S0026-2714(00)00063-9.
^Ott, Henry W. (1976), Noise Reduction Techniques in Electronic Systems, John Wiley, pp. 208, 218, ISBN 0-471-65726-3
^Steinbach, Andrew; Martinis, John; Devoret, Michel (1996-05-13). "Observation of Hot-Electron Shot Noise in a Metallic Resistor". Phys. Rev. Lett. 76 (20): 38.6–38.9. Bibcode:1996PhRvL..76...38M. doi:10.1103/PhysRevLett.76.38.
^Communication Theory. Technical Publications. 1991. p. 3–6. ISBN 9788184314472.
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White noise calculator, thermal noise - Voltage in microvolts, conversion to noise level in dBu and dBV and vice versa
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).
Scherz, Paul. (2006, Nov 14) Practical Electronics for Inventors. ed. McGraw-Hill.
Further reading
Sh. Kogan (1996). Electronic Noise and Fluctuations in Solids. Cambridge University Press. ISBN 0-521-46034-4.
External links
Active Filter (Sallen & Key) Noise Study
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Noise (physics and telecommunications)
General
Acoustic quieting
Distortion
Noise cancellation
Noise control
Noise measurement
Noise power
Noise reduction
Noise temperature
Phase distortion
Noise in...
Audio
Buildings
Electronics
Environment
Government regulation
Human health
Images
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Transportation
Video
Class of noise
Additive white Gaussian noise (AWGN)
Atmospheric noise
Background noise
Brownian noise
Burst noise
Cosmic noise
Flicker noise
Gaussian noise
Grey noise
Jitter
Johnson–Nyquist noise (thermal noise)
Pink noise
Quantization error (or q. noise)
Shot noise
White noise
Coherent noise
Value noise
Gradient noise
Worley noise
Engineering terms
Channel noise level
Circuit noise level
Effective input noise temperature
Equivalent noise resistance
Equivalent pulse code modulation noise
Impulse noise (audio)
Noise figure
Noise floor
Noise shaping
Noise spectral density
Noise, vibration, and harshness (NVH)
Phase noise
Pseudorandom noise
Statistical noise
Ratios
Carrier-to-noise ratio (C/N)
Carrier-to-receiver noise density (C/kT)
dBrnC
Eb/N0 (energy per bit to noise density)
Es/N0 (energy per symbol to noise density)
Modulation error ratio (MER)
Signal, noise and distortion (SINAD)
Signal-to-interference ratio (S/I)
Signal-to-noise ratio (S/N, SNR)
Signal-to-noise ratio (imaging)
Signal to noise plus interference (SNIR)
Signal-to-quantization-noise ratio (SQNR)
Contrast-to-noise ratio (CNR)
Related topics
List of noise topics
Acoustics
Colors of noise
Interference (communication)
Noise generator
Radio noise source
Spectrum analyzer
Thermal radiation
Denoise methods
General
Low-pass filter
Median filter
Total variation denoising
Wavelet denoising
2D (Image)
Gaussian blur
Anisotropic diffusion
Bilateral filter
Non-local means
Block-matching and 3D filtering (BM3D)
Shrinkage Fields
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Analog television broadcasting topics
Systems
180-line
405-line ( System A )
441-line
525-line ( System J , System M )
625-line ( System B , System C , System D , System G , System H , System I , System K , System L , System N )
819-line ( System E , System F )
Color systems
NTSC
PAL
PAL-M
PAL-S
PALplus
SECAM
Video
Back porch and front porch
Black level
Blanking level
Chrominance
Chrominance subcarrier
Colorburst
Color killer
Color TV
Composite video
Frame (video)
Horizontal scan rate
Horizontal blanking interval
Luma
Nominal analogue blanking
Overscan
Raster scan
Safe area
Television lines
Vertical blanking interval
White clipper
Sound
Multichannel television sound
NICAM
Sound-in-Syncs
Zweikanalton
Modulation
Frequency modulation
Quadrature amplitude modulation
Vestigial sideband modulation (VSB)
Transmission
Amplifiers
Antenna (radio)
Broadcast transmitter/Transmitter station
Cavity amplifier
Differential gain
Differential phase
Diplexer
Dipole antenna
Dummy load
Frequency mixer
Intercarrier method
Intermediate frequency
Output power of an analog TV transmitter
Pre-emphasis
Residual carrier
Split sound system
Superheterodyne transmitter
Television receive-only
Direct-broadcast satellite television
Television transmitter
Terrestrial television
Transposer
Digital television transition
Frequencies & Bands
Frequency offset
Microwave transmission
Television channel frequencies
UHF
VHF
Propagation
Beam tilt
Distortion
Earth bulge
Field strength in free space
Knife-edge effect
Noise (electronics)
Null fill
Path loss
Radiation pattern
Skew
Television interference
Testing
Distortionmeter
Field strength meter
Vectorscope
VIT signals
Zero reference pulse
Artifacts
Dot crawl
Ghosting
Hanover bars
Sparklies
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