Telecommunication is the transmission of signs, messages, writings and sounds or information of any nature by wire, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology, it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. Since the Latin term communicatio is considered the social process of information exchange, the term telecommunications is used in its plural form because it involves many different technologies. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, optical heliographs. Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, loud whistles. 20th- and 21st-century technologies for long-distance communication involve electrical and electromagnetic technologies, such as telegraph and teleprinter, radio, microwave transmission, fiber optics, communications satellites.
A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909, other notable pioneering inventors and developers in the field of electrical and electronic telecommunications. These included Charles Wheatstone and Samuel Morse, Alexander Graham Bell, Edwin Armstrong and Lee de Forest, as well as Vladimir K. Zworykin, John Logie Baird and Philo Farnsworth; the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, the Latin communicare, meaning to share. Its modern use is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié. Communication was first used as an English word in the late 14th century, it comes from Old French comunicacion, from Latin communicationem, noun of action from past participle stem of communicare "to share, divide out.
Homing pigeons have been used throughout history by different cultures. Pigeon post had Persian roots, was used by the Romans to aid their military. Frontinus said; the Greeks conveyed the names of the victors at the Olympic Games to various cities using homing pigeons. In the early 19th century, the Dutch government used the system in Sumatra, and in 1849, Paul Julius Reuter started a pigeon service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. In the Middle Ages, chains of beacons were used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London. In 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris.
However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres. As a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. On 25 July 1837 the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke, English scientist Sir Charles Wheatstone. Both inventors viewed their device as "an improvement to the electromagnetic telegraph" not as a new device. Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837, his code was an important advance over Wheatstone's signaling method. The first transatlantic telegraph cable was completed on 27 July 1866, allowing transatlantic telecommunication for the first time; the conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876. Antonio Meucci invented the first device that allowed the electrical transmission of voice over a line in 1849.
However Meucci's device was of little practical value because it relied upon the electrophonic effect and thus required users to place the receiver in their mouth to "hear" what was being said. The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. Starting in 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using the newly discovered phenomenon of radio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean; this was the start of wireless telegraphy by radio. Voice and music had little early success. World War I accelerated the development of radio for military communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated development of radio for the wartime purposes of aircraft and land communication, radio navigation and radar. Development of stereo FM broadcasting of radio
Noise is unwanted sound judged to be unpleasant, loud or disruptive to hearing. From a physics standpoint, noise is indistinguishable from sound, as both are vibrations through a medium, such as air or water; the difference arises when the brain perceives a sound. Acoustic noise is any deliberate or unintended. In contrast, noise in electronics may not be audible to the human ear and may require instruments for detection. In audio engineering, noise can refer to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as a hiss; this signal noise is measured using A-weighting or ITU-R 468 weighting. In experimental sciences, noise can refer to any random fluctuations of data that hinders perception of a signal. Sound is measured based on the frequency of a sound wave. Amplitude measures; the energy in a sound wave is measured in decibels, the measure of loudness, or intensity of a sound. Decibels are expressed in a logarithmic scale. On the other hand, pitch is measured in hertz.
The main instrument to measure sounds in the air is the Sound Level Meter. There are many different varieties of instruments that are used to measure noise - Noise Dosimeters are used in occupational environments, noise monitors are used to measure environmental noise and noise pollution, smartphone-based sound level meter applications are being used to crowdsource and map recreational and community noise. A-weighting is applied to a sound spectrum to represent the sound that humans are capable of hearing at each frequency. Sound pressure is thus expressed in terms of dBA. 0 dBA is the softest level that a person can hear. Normal speaking voices are around 65 dBA. A rock concert can be about 120 dBA. In audio and broadcast systems, audio noise refers to the residual low-level sound, heard in quiet periods of program; this variation from the expected pure sound or silence can be caused by the audio recording equipment, the instrument, or ambient noise in the recording room. In audio engineering it can refer either to the acoustic noise from loudspeakers or to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as'hiss'.
This signal noise is measured using A-weighting or ITU-R 468 weighting Noise is generated deliberately and used as a test signal for audio recording and reproduction equipment. White noise is energy randomly spread across a wide frequency band containing all notes from high to low, it is called "white" noise as it is analogous to "white" light which contains all the colors of the visible spectrum. Environmental noise is the accumulation of all noise present in a specified environment; the principal sources of environmental noise are surface motor vehicles, aircraft and industrial sources. These noise sources expose millions of people to noise pollution that creates not only annoyance, but significant health consequences such as elevated incidence of hearing loss and cardiovascular disease. There are a variety of mitigation strategies and controls available to reduce sound levels including source intensity reduction, land-use planning strategies, noise barriers and sound baffles, time of day use regimens, vehicle operational controls and architectural acoustics design measures.
Certain geographic areas or specific occupations may be at a higher risk of being exposed to high levels of noise. Noise regulation includes statutes or guidelines relating to sound transmission established by national, state or provincial and municipal levels of government. Environmental noise is governed by laws and standards which set maximum recommended levels of noise for specific land uses, such as residential areas, areas of outstanding natural beauty, or schools; these standards specify measurement using a weighting filter, most A-weighting. In 1972, the Noise Control Act was passed to promote a healthy living environment for all Americans, where noise does not pose a threat to human health; this policy's main objectives were: establish coordination of research in the area of noise control, establish federal standards on noise emission for commercial products, promote public awareness about noise emission and reduction. The Quiet Communities Act of 1978 promotes noise control programs at the state and local level and developed a research program on noise control.
Both laws authorized the Environmental Protection Agency to study the effects of noise and evaluate regulations regarding noise control. The National Institute for Occupational Safety and Health provides recommendation on noise exposure in the workplace. In 1972, NIOSH published a document outlining recommended standards relating to the occupational exposure to noise, with the purpose of reducing the risk of developing permanent hearing loss related to exposure at work; this publication set the recommended exposure limit of noise in an occupation setting to 85 dBA for 8 hours using a 3-dB exchange rate. However, in 1973 the Occupational Safety and Health Administration maintained the requirement of an 8-hour average of 90 dBA; the following year, OSHA required employers to provide a hearing conservation program to workers exposed to 85 dBA average 8-hour workdays. The European Environment Agency regulates noise control and surveillance within the European Union
Signal integrity or SI is a set of measures of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage waveform. However, digital signals are fundamentally analog in nature, all signals are subject to effects such as noise and loss. Over short distances and at low bit rates, a simple conductor can transmit this with sufficient fidelity. At high bit rates and over longer distances or through various mediums, various effects can degrade the electrical signal to the point where errors occur and the system or device fails. Signal integrity engineering is the task of mitigating these effects, it is an important activity at all levels of electronics packaging and assembly, from internal connections of an integrated circuit, through the package, the printed circuit board, the backplane, inter-system connections. While there are some common themes at these various levels, there are practical considerations, in particular the interconnect flight time versus the bit period, that cause substantial differences in the approach to signal integrity for on-chip connections versus chip-to-chip connections.
Some of the main issues of concern for signal integrity are ringing, ground bounce, signal loss, power supply noise. Signal integrity involves the electrical performance of the wires and other packaging structures used to move signals about within an electronic product; such performance is a matter of basic physics and as such has remained unchanged since the inception of electronic signaling. The first transatlantic telegraph cable suffered from severe signal integrity problems, analysis of the problems yielded many of the mathematical tools still used today to analyze signal integrity problems, such as the telegrapher's equations. Products as old as the Western Electric crossbar telephone exchange, based on the wire-spring relay, suffered all the effects seen today - the ringing, ground bounce, power supply noise that plague modern digital products. On printed circuit boards, signal integrity became a serious concern when the transition times of signals started to become comparable to the propagation time across the board.
Speaking, this happens when system speeds exceed a few tens of MHz. At first, only a few of the most important, or highest speed, signals needed detailed analysis or design; as speeds increased, a larger and larger fraction of signals needed SI analysis and design practices. In modern circuit designs all signals must be designed with SI in mind. For ICs, SI analysis became necessary as an effect of reduced design rules. In the early days of the modern VLSI era, digital chip circuit design and layout were manual processes; the use of abstraction and the application of automatic synthesis techniques have since allowed designers to express their designs using high-level languages and apply an automated design process to create complex designs, ignoring the electrical characteristics of the underlying circuits to a large degree. However, scaling trends brought electrical effects back to the forefront in recent technology nodes. With scaling of technology below 0.25 µm, the wire delays have become comparable or greater than the gate delays.
As a result, the wire delays needed to be considered to achieve timing closure. In nanometer technologies at 0.13 µm and below, unintended interactions between signals became an important consideration for digital design. At these technology nodes, the performance and correctness of a design cannot be assured without considering noise effects. Most of this article is about SI in relation to modern electronic technology - notably the use integrated circuits and printed circuit board technology; the principles of SI are not exclusive to the signalling technology used. SI existed long before the advent of either technology, will do so as long as electronic communications persist. Signal integrity problems in modern integrated circuits can have many drastic consequences for digital designs: Products can fail to operate at all, or worse yet, become unreliable in the field; the design may work, but only at speeds slower than planned Yield may be lowered, sometimes drasticallyThe cost of these failures is high, includes photomask costs, engineering costs and opportunity cost due to delayed product introduction.
Therefore, electronic design automation tools have been developed to analyze and correct these problems. In integrated circuits, or ICs, the main cause of signal integrity problems is crosstalk. In CMOS technologies, this is due to coupling capacitance, but in general it may be caused by mutual inductance, substrate coupling, non-ideal gate operation, other sources; the fixes involve changing the sizes of drivers and/or spacing of wires. In analog circuits, designers are concerned with noise that arise from physical sources, such as thermal noise, flicker noise, shot noise; these noise sources on the one hand present a lower limit to the smallest signal that can be amplified, on the other, define an upper limit to the useful amplification. In digital ICs, noise in a signal of interest arises from coupling effects from switching of other signals. Increasing interconnect density has led to each wire having neighbors that are physically closer together, leading to increased crosstalk between neighboring nets.
As circuits have continued to shrink in accordance with Moore's law, several effects have conspired to make noise problems worse: To keep resistance tolerable despite decreased width, modern wire geometries are thicker in propo
A digital signal is a signal, being used to represent data as a sequence of discrete values. This contrasts with an analog signal. Simple digital signals represent information in discrete bands of analog levels. All levels within a band of values represent the same information state. In most digital circuits, the signal can have two possible values, they are represented by two voltage bands: one near a reference value, the other a value near the supply voltage. These correspond to the two values "zero" and "one" of the Boolean domain, so at any given time a binary signal represents one binary digit; because of this discretization small changes to the analog signal levels do not leave the discrete envelope, as a result are ignored by signal state sensing circuitry. As a result, digital signals have noise immunity. Digital signals having more than two states are used. For example, signals that can assume three possible states are called three-valued logic. In a digital signal, the physical quantity representing the information may be a variable electric current or voltage, the intensity, phase or polarization of an optical or other electromagnetic field, acoustic pressure, the magnetization of a magnetic storage media, etcetera.
Digital signals are used in all digital electronics, notably computing equipment and data transmission. The term digital signal has related definitions in different contexts. In digital electronics a digital signal is a pulse train, i.e. a sequence of fixed-width square-wave electrical pulses or light pulses, each occupying one of a discrete number of levels of amplitude. A special case is a logic signal or a binary signal, which varies between a low and a high signal level. In digital signal processing, a digital signal is a representation of a physical signal, a sampled and quantized. A digital signal is an abstraction, discrete in time and amplitude; the signal's value only exists at regular time intervals, since only the values of the corresponding physical signal at those sampled moments are significant for further digital processing. The digital signal is a sequence of codes drawn from a finite set of values; the digital signal may be stored, processed or transmitted physically as a pulse-code modulation signal.
In digital communications, a digital signal is a continuous-time physical signal, alternating between a discrete number of waveforms, representing a bitstream. The shape of the waveform depends the transmission scheme, which may be either a line coding scheme allowing baseband transmission; such a carrier-modulated sine wave is considered a digital signal in literature on digital communications and data transmission, but considered as a bitstream converted to an analog signal in electronics and computer networking. In communications, sources of interference are present, noise is a significant problem; the effects of interference are minimized by filtering off interfering signals as much as possible and by using data redundancy. The main advantages of digital signals for communications are considered to be the noise immunity to noise capability, the ability, in many cases such as with audio and video data, to use data compression to decrease the bandwidth, required on the communication media.
A waveform that switches representing the two states of a Boolean value is referred to as a digital signal or logic signal or binary signal when it is interpreted in terms of only two possible digits. The two states are represented by some measurement of an electrical property: Voltage is the most common, but current is used in some logic families. A threshold is designed for each logic family; when below that threshold, the signal is low. The clock signal is a special digital signal, used to synchronize many digital circuits; the image shown can be considered the waveform of a clock signal. Logic changes are triggered either by the falling edge; the rising edge is the transition from a low voltage to a high voltage. The falling edge is the transition from a high voltage to a low one. Although in a simplified and idealized model of a digital circuit, we may wish for these transitions to occur instantaneously, no real world circuit is purely resistive and therefore no circuit can change voltage levels.
This means that during a short, finite transition time the output may not properly reflect the input, will not correspond to either a logically high or low voltage. To create a digital signal, an analog signal must be modulated with a control signal to produce it; the simplest modulation, a type of unipolar encoding, is to switch on and off a DC signal, so that high voltages represent a'1' and low voltages are'0'. In digital radio schemes one or more carrier waves are amplitude, frequency or phase modulated by the control signal to produce a digital signal suitable for transmission. Asymmetric Digital Subscriber Line over telephone wires, does not use binary logic.
In electronics, noise is an unwanted disturbance in an electrical signal. Noise generated by electronic devices varies 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 distinguished from interference, for example in the signal-to-noise ratio, signal-to-interference ratio and signal-to-noise plus interference ratio measures. Noise is typically distinguished from distortion, an unwanted systematic alteration of the signal waveform by the communication equipment, for example in signal-to-noise and distortion ratio and total harmonic distortion plus noise measures. While noise is unwanted, it can serve a useful purpose in some applications, such as random number generation or dither. Different types of noise are generated by different processes. Thermal noise is unavoidable at non-zero temperature, while other types depend on device type or manufacturing quality and semiconductor defects, such as conductance fluctuations, including 1/f noise.
Johnson–Nyquist noise is unavoidable, generated by the random thermal motion of charge carriers, inside an electrical conductor, which happens regardless of any applied voltage. Thermal noise is white, meaning that its power spectral density is nearly equal throughout the frequency spectrum; the amplitude of the signal has nearly a Gaussian probability density function. A communication system affected by thermal noise is modeled as an additive white Gaussian noise channel. Shot noise in electronic devices results from unavoidable random statistical fluctuations of the electric current when the charge carriers traverse a gap. If electrons flow across a barrier they have discrete arrival times; those discrete arrivals exhibit shot noise. The barrier in a diode is used. Shot noise is similar to the noise created by rain falling on a tin roof; the flow of rain may be constant, but the individual raindrops arrive discretely. The root-mean-square value of the shot noise current in is given by the Schottky formula.
I n = 2 I q Δ B where I is the DC current, q is the charge of an electron, 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. A tube may not exhibit the full shot noise effect: the presence of a space charge tends to smooth out the arrival times. Conductors and resistors do not exhibit shot noise because the electrons thermalize and move diffusively within the material. Shot noise has been demonstrated in mesoscopic resistors when the size of the resistive element becomes shorter than the electron–phonon scattering length. Flicker noise known as 1/f noise, is a signal or process with a frequency spectrum that falls off into the higher frequencies, with a pink spectrum, it occurs in all electronic devices and results from a variety of effects. 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 known a popcorn noise for the popping or crackling sounds it produces in audio circuits. 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 dominates other sources of noise. 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. Intermodulation noise Caused. 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 mediumAtmospheric noise This noise is called static noise and it is the natural source of disturbance caused by lightning discharge in thunderstorm and the natural disturbances occurring in nature. Industrial noise Sources such as automobiles, 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. While these stars are too far away to individually affect
General Services Administration
The General Services Administration, an independent agency of the United States government, was established in 1949 to help manage and support the basic functioning of federal agencies. GSA supplies products and communications for U. S. government offices, provides transportation and office space to federal employees, develops government-wide cost-minimizing policies and other management tasks. GSA employs about 12,000 federal workers and has an annual operating budget of $20.9 billion. GSA oversees $66 billion of procurement annually, it contributes to the management of about $500 billion in U. S. federal property, divided chiefly among 8,700 owned and leased buildings and a 215,000 vehicle motor pool. Among the real estate assets managed by GSA are the Ronald Reagan Building and International Trade Center in Washington, D. C. – the largest U. S. federal building after the Pentagon – and the Hart-Dole-Inouye Federal Center. GSA's business lines include the Federal Acquisition Service and the Public Buildings Service, as well as several Staff Offices including the Office of Government-wide Policy, the Office of Small Business Utilization, the Office of Mission Assurance.
As part of FAS, GSA's Technology Transformation Services helps federal agencies improve delivery of information and services to the public. Key initiatives include FedRAMP, Cloud.gov, the USAGov platform, Data.gov, Performance.gov, Challenge.gov. GSA is a member of the Procurement G6, an informal group leading the use of framework agreements and e-procurement instruments in public procurement. In 1947 President Harry Truman asked former President Herbert Hoover to lead what became known as the Hoover Commission to make recommendations to reorganize the operations of the federal government. One of the recommendations of the commission was the establishment of an "Office of the General Services." This proposed office would combine the responsibilities of the following organizations: U. S. Treasury Department's Bureau of Federal Supply U. S. Treasury Department's Office of Contract Settlement National Archives Establishment All functions of the Federal Works Agency, including the Public Buildings Administration and the Public Roads Administration War Assets AdministrationGSA became an independent agency on July 1, 1949, after the passage of the Federal Property and Administrative Services Act.
General Jess Larson, Administrator of the War Assets Administration, was named GSA's first Administrator. The first job awaiting Administrator Larson and the newly formed GSA was a complete renovation of the White House; the structure had fallen into such a state of disrepair by 1949 that one inspector of the time said the historic structure was standing "purely from habit." Larson explained the nature of the total renovation in depth by saying, "In order to make the White House structurally sound, it was necessary to dismantle, I mean dismantle, everything from the White House except the four walls, which were constructed of stone. Everything, except the four walls without a roof, was stripped down, that's where the work started." GSA worked with President Truman and First Lady Bess Truman to ensure that the new agency's first major project would be a success. GSA completed the renovation in 1952. In 1986 GSA headquarters, U. S. General Services Administration Building, located at Eighteenth and F Streets, NW, was listed on the National Register of Historic Places, at the time serving as Interior Department offices.
In 1960 GSA created the Federal Telecommunications System, a government-wide intercity telephone system. In 1962 the Ad Hoc Committee on Federal Office Space created a new building program to address obsolete office buildings in Washington, D. C. resulting in the construction of many of the offices that now line Independence Avenue. In 1970 the Nixon administration created the Consumer Product Information Coordinating Center, now part of USAGov. In 1974 the Federal Buildings Fund was initiated, allowing GSA to issue rent bills to federal agencies. In 1972 GSA established the Automated Data and Telecommunications Service, which became the Office of Information Resources Management. In 1973 GSA created the Office of Federal Management Policy. GSA's Office of Acquisition Policy centralized procurement policy in 1978. GSA was responsible for emergency preparedness and stockpiling strategic materials to be used in wartime until these functions were transferred to the newly-created Federal Emergency Management Agency in 1979.
In 1984 GSA introduced the federal government to the use of charge cards, known as the GMA SmartPay system. The National Archives and Records Administration was spun off into an independent agency in 1985; the same year, GSA began to provide governmentwide policy oversight and guidance for federal real property management as a result of an Executive Order signed by President Ronald Reagan. In 2003 the Federal Protective Service was moved to the Department of Homeland Security. In 2005 GSA reorganized to merge the Federal Supply Service and Federal Technology Service business lines into the Federal Acquisition Service. On April 3, 2009, President Barack Obama nominated Martha N. Johnson to serve as GSA Administrator. After a nine-month delay, the United States Senate confirmed her nomination on February 4, 2010. On April 2, 2012, Johnson resigned in the wake of a management-deficiency report that detailed improper payments for a 2010 "Western Regions" training conference put on by the Public Buildings Service in Las Vegas.
In July 1991 GSA contractors began the excavation of what is now the Ted Weiss Federal Building in New York City. The planning for that buildin
In signal processing, control theory and mathematics, overshoot is the occurrence of a signal or function exceeding its target. It arises in the step response of bandlimited systems such as low-pass filters, it is followed by ringing, at times conflated with the latter. Maximum overshoot is defined in Katsuhiko Ogata's Discrete-time control systems as "the maximum peak value of the response curve measured from the desired response of the system." In control theory, overshoot refers to an output exceeding its steady-state value. For a step input, the percentage overshoot is the maximum value minus the step value divided by the step value. In the case of the unit step, the overshoot is just the maximum value of the step response minus one. See the definition of overshoot in an electronics context. For second order systems, the percentage overshoot is a function of the damping ratio ζ and is given by P O = 100 ⋅ e The damping ratio can be found by ζ = 2 π 2 + 2 In electronics, overshoot refers to the transitory values of any parameter that exceeds its final value during its transition from one value to another.
An important application of the term is to the output signal of an amplifier. Usage: Overshoot occurs when the transitory values exceed final value; when they are lower than the final value, the phenomenon is called "undershoot". A circuit is designed to minimize risetime while containing distortion of the signal within acceptable limits. Overshoot represents a distortion of the signal. In circuit design, the goals of minimizing overshoot and of decreasing circuit risetime can conflict; the magnitude of overshoot depends on time through a phenomenon called "damping." See illustration under step response. Overshoot is associated with settling time, how long it takes for the output to reach steady state. See the definition of overshoot in a control theory context. In the approximation of functions, overshoot is one term describing quality of approximation; when a function such as a square wave is represented by a summation of terms, for example, a Fourier series or an expansion in orthogonal polynomials, the approximation of the function by a truncated number of terms in the series can exhibit overshoot and ringing.
The more terms retained in the series, the less pronounced the departure of the approximation from the function it represents. However, though the period of the oscillations decreases, their amplitude does not. For the Fourier transform, this can be modeled by approximating a step function by the integral up to a certain frequency, which yields the sine integral; this can be interpreted as convolution with the sinc function. In signal processing, overshoot is when the output of a filter has a higher maximum value than the input for the step response, yields the related phenomenon of ringing artifacts; this occurs for instance in using the sinc filter as an ideal low-pass filter. The step response can be interpreted as the convolution with the impulse response, a sinc function; the overshoot and undershoot can be understood in this way: kernels are normalized to have integral 1, so they send constant functions to constant functions – otherwise they have gain. The value of a convolution at a point is a linear combination of the input signal, with coefficients the values of the kernel.
If a kernel is non-negative, such as for a Gaussian kernel the value of the filtered signal will be a convex combination of the input values, will thus fall between the minimum and maximum of the input signal – it will not undershoot or overshoot. If, on the other hand, the kernel assumes negative values, such as the sinc function the value of the filtered signal will instead be an affine combination of the input values, may fall outside of the minimum and maximum of the input signal, resulting in undershoot and overshoot. Overshoot is undesirable if it causes clipping, but is sometimes desirable in image sharpening, due to increasing acutance. A related phenomenon is ringing, following overshoot, a signal falls below its steady-state value, may bounce back above, taking some time to settle close to its steady-state value. In ecology, overshoot is the analogous concept, where a population exceeds the carrying capacity of a system. Step response Ringing Settle time Damping Overmodulation Integral windup Percentage overshoot calculator