Noise (electronics)
Encyclopedia
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic
circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects. Thermal noise is unavoidable at non-zero temperature (see fluctuation-dissipation theorem), while other types depend mostly on device type (such as shot noise
, which needs steep potential barrier) or manufacturing quality and semiconductor
defects, such as conductance fluctuations, including 1/f noise.
In communication systems, the noise is an error or undesired random disturbance of a useful information signal, introduced before or after the detector and decoder. The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources. Noise is, however, typically distinguished from interference
, (e.g. cross-talk, deliberate jamming
or other unwanted electromagnetic interference
from specific transmitters), 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 alteration of the signal waveform, for example in the signal-to-noise and distortion ratio (SINAD). 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 (BER).
While noise is generally unwanted, it can serve a useful purpose in some applications, such as random number generation
or dithering.
s), 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.
The root mean square
(RMS) voltage due to thermal noise
, generated in a resistance R (ohms
) over bandwidth Δf (hertz
), is given by
where kB is Boltzmann's constant (joule
s per kelvin
) and T is the resistor's absolute temperature
(kelvin).
As the amount of thermal noise generated depends upon the temperature of the circuit, very sensitive circuits such as preamplifier
s in radio telescope
s are sometimes cooled in liquid nitrogen
to reduce the noise level.
in an electrical conductor. Random fluctuations are inherent when current flows, as the current is a flow of discrete charges (electron
s).
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, though always related to a direct current.
), as high as several hundred microvolts, 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 Hz
), leading to the term popcorn noise for the popping or crackling sounds it produces in audio circuits.
, a semiconductor junction phenomenon in which carriers in a high voltage gradient develop sufficient energy to dislodge additional carriers through physical impact, creating ragged current flows.
s 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 coversion 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 decibel
s (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. Noise in telecommunication systems is a product of both internal and external sources to the system.
, 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
.
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects. Thermal noise is unavoidable at non-zero temperature (see fluctuation-dissipation theorem), while other types depend mostly on device type (such as shot noise
Shot noise
Shot noise is a type of electronic noise that may be dominant when the finite number of particles that carry energy is sufficiently small so that uncertainties due to the Poisson distribution, which describes the occurrence of independent random events, are of significance...
, which needs steep potential barrier) or manufacturing quality and semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
defects, such as conductance fluctuations, including 1/f noise.
In communication systems, the noise is an error or undesired random disturbance of a useful information signal, introduced before or after the detector and decoder. The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources. Noise is, however, typically distinguished from interference
Interference (communication)
In communications and electronics, especially in telecommunications, interference is anything which alters, modifies, or disrupts a signal as it travels along a channel between a source and a receiver. The term typically refers to the addition of unwanted signals to a useful signal...
, (e.g. cross-talk, deliberate jamming
Radio jamming
Radio jamming is the transmission of radio signals that disrupt communications by decreasing the signal to noise ratio. Unintentional jamming occurs when an operator transmits on a busy frequency without first checking whether it is in use, or without being able to hear stations using the frequency...
or other unwanted electromagnetic interference
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
from specific transmitters), for example in the signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
(SNR), signal-to-interference ratio
Signal-to-interference ratio
The signal-to-interference ratio , also known as the carrier-to-interference ratio , is the quotient between the average received modulated carrier power S or C and the average received co-channel interference power I, i.e...
(SIR) and signal-to-noise plus interference ratio (SNIR) measures. Noise is also typically distinguished from distortion
Distortion
A distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...
, which is an unwanted alteration of the signal waveform, for example in the signal-to-noise and distortion ratio (SINAD). In a carrier-modulated passband analog communication system, a certain carrier-to-noise ratio
Carrier-to-noise ratio
In telecommunications, the carrier-to-noise ratio, often written CNR or C/N, is the signal-to-noise ratio of a modulated signal. The term is used to distinguish the CNR of the radio frequency passband signal from the SNR of an analogue base band message signal after demodulation, for example an...
(CNR) at the radio receiver input would result in a certain signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
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 (BER).
While noise is generally unwanted, it can serve a useful purpose in some applications, such as random number generation
Random number generation
A random number generator ) is a computational or physical device designed to generate a sequence of numbers or symbols that lack any pattern, i.e. appear random....
or dithering.
Thermal noise
Johnson–Nyquist noise (sometimes thermal, Johnson or Nyquist noise) is unavoidable, and generated by the random thermal motion of charge carriers (usually electronElectron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s), inside an electrical conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
, which happens regardless of any applied voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
.
Thermal noise is approximately white
White noise
White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
, meaning that its power spectral density is nearly equal throughout the frequency spectrum
Frequency spectrum
The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain. The frequency spectrum can be generated via a Fourier transform of the signal, and the resulting values are usually presented as amplitude and phase, both plotted versus frequency.Any signal...
. The amplitude of the signal has very nearly a Gaussian
GAUSSIAN
Gaussian is a computational chemistry software program initially released in 1970 by John Pople and his research group at Carnegie-Mellon University as Gaussian 70. It has been continuously updated since then...
probability density function
Probability density function
In probability theory, a probability density function , or density of a continuous random variable is a function that describes the relative likelihood for this random variable to occur at a given point. The probability for the random variable to fall within a particular region is given by the...
. A communication system affected by thermal noise is often modeled as an additive white Gaussian noise
Additive white Gaussian noise
Additive white Gaussian noise is a channel model in which the only impairment to communication is a linear addition of wideband or white noise with a constant spectral density and a Gaussian distribution of amplitude. The model does not account for fading, frequency selectivity, interference,...
(AWGN) channel.
The root mean square
Root mean square
In mathematics, the root mean square , also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids...
(RMS) voltage due to thermal noise
, generated in a resistance R (ohmsOhms
OHMS may refer to:* The plural of ohm, a unit of resistance, named after Georg Ohm* Ohm's Law of electric currents, first proposed by Georg Ohm* O.H.M.S., On His/Her Majesty's Service...
) over bandwidth Δf (hertz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
), is given by
where kB is Boltzmann's constant (joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
s per kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
) and T is the resistor's absolute temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
(kelvin).
As the amount of thermal noise generated depends upon the temperature of the circuit, very sensitive circuits such as preamplifier
Preamplifier
A preamplifier is an electronic amplifier that prepares a small electrical signal for further amplification or processing. A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main...
s in radio telescope
Radio telescope
A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...
s are sometimes cooled in liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...
to reduce the noise level.
Shot noise
Shot noise in electronic devices consists of unavoidable random statistical fluctuations of the electric currentElectric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
in an electrical conductor. Random fluctuations are inherent when current flows, as the current is a flow of discrete charges (electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s).
Flicker noise
Flicker noise, also known as 1/f noise, is a signal or process with a frequency spectrumFrequency spectrum
The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain. The frequency spectrum can be generated via a Fourier transform of the signal, and the resulting values are usually presented as amplitude and phase, both plotted versus frequency.Any signal...
that falls off steadily into the higher frequencies, with a pink
Pink noise
Pink noise or 1/ƒ noise is a signal or process with a frequency spectrum such that the power spectral density is inversely proportional to the frequency. In pink noise, each octave carries an equal amount of noise power...
spectrum. It occurs in almost all electronic devices, and results from a variety of effects, though always related to a direct current.
Burst noise
Burst noise consists of sudden step-like transitions between two or more levels (non-GaussianGAUSSIAN
Gaussian is a computational chemistry software program initially released in 1970 by John Pople and his research group at Carnegie-Mellon University as Gaussian 70. It has been continuously updated since then...
), as high as several hundred microvolts, 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 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
), leading to the term popcorn noise for the popping or crackling sounds it produces in audio circuits.
Avalanche noise
Avalanche noise is the noise produced when a junction diode is operated at the onset of avalanche breakdownAvalanche breakdown
Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. It is a type of electron avalanche...
, a semiconductor junction phenomenon in which carriers in a high voltage gradient develop sufficient energy to dislodge additional carriers through physical impact, creating ragged current flows.
Quantification
The noise level in an electronic system is typically measured as an electrical power N in wattWatt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s or dBm
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
, a root mean square
Root mean square
In mathematics, the root mean square , also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids...
(RMS) voltage (identical to the noise standard deviation
Standard deviation
Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...
) in volts, dBμV
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
or a mean squared error
Mean squared error
In statistics, the mean squared error of an estimator is one of many ways to quantify the difference between values implied by a kernel density estimator and the true values of the quantity being estimated. MSE is a risk function, corresponding to the expected value of the squared error loss or...
(MSE) in volts squared. Noise may also be characterized by its probability distribution
Probability distribution
In probability theory, a probability mass, probability density, or probability distribution is a function that describes the probability of a random variable taking certain values....
and noise spectral density
Noise spectral density
In communications, noise spectral density No is the noise power per unit of bandwidth; that is, it is the power spectral density of the noise. It has dimension of power/frequency , whose SI coherent unit is watts per hertz, which is equivalent to watt-seconds or joules...
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
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
(SNR or S/N), signal-to-quantization noise ratio (SQNR) in analog-to-digital coversion and compression, peak signal-to-noise ratio
Peak signal-to-noise ratio
The phrase peak signal-to-noise ratio, often abbreviated PSNR, is an engineering term for the ratio between the maximum possible power of a signal and the power of corrupting noise that affects the fidelity of its representation...
(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
Noise figure
Noise figure is a measure of degradation of the signal-to-noise ratio , caused by components in a radio frequency signal chain. The noise figure is defined as the ratio of the output noise power of a device to the portion thereof attributable to thermal noise in the input termination at standard...
in cascaded amplifiers.
Noise is a random process, characterized by stochastic
Stochastic process
In probability theory, a stochastic process , or sometimes random process, is the counterpart to a deterministic process...
properties such as its variance
Variance
In probability theory and statistics, the variance is a measure of how far a set of numbers is spread out. It is one of several descriptors of a probability distribution, describing how far the numbers lie from the mean . In particular, the variance is one of the moments of a distribution...
, distribution
Probability distribution
In probability theory, a probability mass, probability density, or probability distribution is a function that describes the probability of a random variable taking certain values....
, and spectral density
Spectral density
In statistical signal processing and physics, the spectral density, power spectral density , or energy spectral density , is a positive real function of a frequency variable associated with a stationary stochastic process, or a deterministic function of time, which has dimensions of power per hertz...
. The spectral distribution of noise can vary with frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
, so its power density is measured in watts per hertz (W/Hz). Since the power in a resistive
Resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
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 circuitIntegrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
devices, such as operational amplifiers commonly quote equivalent input noise level in these terms (at room temperature).
Noise power is measured in Watts or decibel
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
s (dB) relative to a standard power, usually indicated by adding a suffix after dB. Examples of electrical noise-level measurement units are dBu
DBU
DBU may refer to:* Dansk Boldspil-Union, in English known as the Danish Football Association* dBu, a decibel measurement of voltage* 1,8-Diazabicyclo[5.4.0]undec-7-ene...
, dBm0
DBm0
dBm0 is an abbreviation for the power in dBm measured at a zero transmission level point.dBm0 is a concept used in audio/telephony processing since it allows a smooth integration of analog and digital chains...
, dBrn
DBrn
The symbol dBrn or dB is an abbreviation for decibels above reference noise.Weighted noise power in dB is referred to 1.0 picowatt. Thus, 0 dBrn = -90 dBm...
, dBrnC
DBrnC
dBrnC represents an audio level measurement, typically in a telephone circuit, relative to the circuit noise level, with the measurement of this level frequency-weighted by a standard C-message weighting filter. The C-message weighting filter was chiefly used in North America. The Psophometric...
, and dBrn(f1 − f2), dBrn(144-line
Line (electrical engineering)
In electrical engineering, a line is, more generally, any circuit of an electrical system. This electric circuit loop , consists of electrical elements connected directly by conductor terminals to other devices in series....
).
Noise levels are usually viewed in opposition to signal levels and so are often seen as part of a signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
(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
Noise floor
In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system, where the noise is defined as any signal other than the one being monitored....
) in the system, data can no longer be decoded at the receiver. Noise in telecommunication systems is a product of both internal and external sources to the system.
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 ditherDither
Dither is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images...
, 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
Stochastic resonance
Stochastic resonance is a phenomenon that occurs in a threshold measurement system when an appropriate measure of information transfer is maximized in the presence of a non-zero level of stochastic input noise thereby lowering the response...
.