1.
Electronics
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Electronics is the science of controlling electrical energy electrically, in which the electrons have a fundamental role. Commonly, electronic devices contain circuitry consisting primarily or exclusively of active semiconductors supplemented with passive elements, the science of electronics is also considered to be a branch of physics and electrical engineering. The ability of electronic devices to act as switches makes digital information processing possible, until 1950 this field was called radio technology because its principal application was the design and theory of radio transmitters, receivers, and vacuum tubes. Today, most electronic devices use semiconductor components to perform electron control and this article focuses on engineering aspects of electronics. Components are generally intended to be connected together, usually by being soldered to a circuit board. Components may be packaged singly, or in more complex groups as integrated circuits, some common electronic components are capacitors, inductors, resistors, diodes, transistors, etc. Components are often categorized as active or passive, vacuum tubes were among the earliest electronic components. They were almost solely responsible for the revolution of the first half of the Twentieth Century. They took electronics from parlor tricks and gave us radio, television, phonographs, radar, long distance telephony and they played a leading role in the field of microwave and high power transmission as well as television receivers until the middle of the 1980s. Since that time, solid state devices have all but completely taken over, vacuum tubes are still used in some specialist applications such as high power RF amplifiers, cathode ray tubes, specialist audio equipment, guitar amplifiers and some microwave devices. The 608 contained more than 3,000 germanium transistors, thomas J. Watson Jr. ordered all future IBM products to use transistors in their design. From that time on transistors were almost exclusively used for computer logic, circuits and components can be divided into two groups, analog and digital. A particular device may consist of circuitry that has one or the other or a mix of the two types, most analog electronic appliances, such as radio receivers, are constructed from combinations of a few types of basic circuits. Analog circuits use a range of voltage or current as opposed to discrete levels as in digital circuits. The number of different analog circuits so far devised is huge, especially because a circuit can be defined as anything from a single component, analog circuits are sometimes called linear circuits although many non-linear effects are used in analog circuits such as mixers, modulators, etc. Good examples of analog circuits include vacuum tube and transistor amplifiers, one rarely finds modern circuits that are entirely analog. These days analog circuitry may use digital or even microprocessor techniques to improve performance and this type of circuit is usually called mixed signal rather than analog or digital. Sometimes it may be difficult to differentiate between analog and digital circuits as they have elements of both linear and non-linear operation, an example is the comparator which takes in a continuous range of voltage but only outputs one of two levels as in a digital circuit
2.
Electron
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The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον
3.
Electrical connector
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An electrical connector, is an electro-mechanical device used to join electrical terminations and create an electrical circuit. Electrical connectors consist of plugs and jacks, the connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or devices. An adapter can be used to bring together dissimilar connectors. There are hundreds of types of electrical connectors, connectors may join two lengths of flexible copper wire or cable, or connect a wire or cable to an electrical terminal. In computing, a connector can also be known as a physical interface. Cable glands, known as cable connectors in the US, connect wires to devices rather than electrically and are distinct from quick-disconnects performing the latter. It is usually desirable for a connector to be easy to visually, rapid to assemble, require only simple tooling. In some cases an equipment manufacturer might choose a connector specifically because it is not compatible with those other sources. No single connector has all the properties, the proliferation of types is a reflection of differing requirements. Fretting is a failure mode in electrical connectors that have not been specifically designed to prevent it. Many connectors are keyed, with some mechanical component which prevents mating except with a correctly oriented matching connector, some connector housings are designed with locking mechanisms to prevent inadvertent disconnection or poor environmental sealing. Locking mechanism designs include locking levers of various sorts, screw locking, a terminal is a simple type of electrical connector that connects two or more wires to a single connection point. Wire nuts are another type of single point connector, terminal blocks provide a convenient means of connecting individual electrical wires without a splice or physically joining the ends. They are usually used to connect wiring among various items of equipment within an enclosure or to make connections among individually enclosed items. Since terminal blocks are available for a wide range of wire sizes and terminal quantity. One type of terminal block accepts wires that are prepared only by removing a short length of insulation from the end, another type accepts wires that have ring or spade terminal lugs crimped onto the wires. Printed circuit board mounted terminal blocks allow individual wires to be connected to the circuit board, a general type of connector that simply screws or clamps bare wire to a post, such connectors are frequently used in electronic test equipment and audio. Many, but not all binding posts will also accept a banana connector plug, since stripping the insulation from wires is time-consuming, many connectors intended for rapid assembly use insulation-displacement connectors so that insulation need not be removed from the wire
4.
Lead (electronics)
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In electronics, a lead is an electrical connection consisting of a length of wire or metal pad that comes from a device. Leads are used for support, to transfer power, to probe circuits, to transmit information. The tiny leads coming off through-hole components are often called pins. IC pins often either bend under the body like a letter J or come out, down. Most kinds of integrated circuit packaging are made by placing the silicon chip on a frame, wire bonding the chip to the metal leads of that lead frame. The metal leads protruding from the plastic are then either cut long and bent to form through-hole pins, or cut short, the lead frame are occasionally made from FeNi42, a kind of Invar. For most circuit designs it can be assumed that the leads do not contribute to the effects of individual components. This assumption begins to break down at higher frequencies and at small scales. These effects come from the construction of the leads. The leads are often metal connections that run from the rest of the circuit to the materials that each component is made of. This design results in a small capacitance between the ends of the leads where they connect to the device and very small inductances and resistances along each lead
5.
Electrical network
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An electrical network is an interconnection of electrical components or a model of such an interconnection, consisting of electrical elements. An electrical circuit is a network consisting of a closed loop, linear electrical networks, a special type consisting only of sources, linear lumped elements, and linear distributed elements, have the property that signals are linearly superimposable. They are thus more easily analyzed, using powerful frequency domain methods such as Laplace transforms, to determine DC response, AC response, a resistive circuit is a circuit containing only resistors and ideal current and voltage sources. Analysis of resistive circuits is less complicated than analysis of circuits containing capacitors and inductors, if the sources are constant sources, the result is a DC circuit. A network that contains active components is known as an electronic circuit. Such networks are generally nonlinear and require more complex design and analysis tools, an active network is a network that contains an active source – either a voltage source or current source. A passive network is a network that does not contain an active source, a network is linear if its signals obey the principle of superposition, otherwise it is non-linear. Sources can be classified as independent sources and dependent sources Ideal Independent Source maintains same voltage or current regardless of the elements present in the circuit. Its value is either constant or sinusoidal, the strength of voltage or current is not changed by any variation in connected network. Dependent Sources depend upon a particular element of the circuit for delivering the power or voltage or current depending upon the type of source it is, a number of electrical laws apply to all electrical networks. These include, Kirchhoffs current law, The sum of all currents entering a node is equal to the sum of all currents leaving the node, Kirchhoffs voltage law, The directed sum of the electrical potential differences around a loop must be zero. Ohms law, The voltage across a resistor is equal to the product of the resistance, nortons theorem, Any network of voltage or current sources and resistors is electrically equivalent to an ideal current source in parallel with a single resistor. Thévenins theorem, Any network of voltage or current sources and resistors is electrically equivalent to a voltage source in series with a single resistor. Other more complex laws may be needed if the network contains nonlinear or reactive components, non-linear self-regenerative heterodyning systems can be approximated. Applying these laws results in a set of equations that can be solved either algebraically or numerically. To design any electrical circuit, either analog or digital, electrical engineers need to be able to predict the voltages, simple linear circuits can be analyzed by hand using complex number theory. In more complex cases the circuit may be analyzed with specialized programs or estimation techniques such as the piecewise-linear model. More complex circuits can be analyzed numerically with software such as SPICE or GNUCAP, once the steady state solution is found, the operating points of each element in the circuit are known
6.
Amplifier
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An amplifier, electronic amplifier or amp is an electronic device that can increase the power of a signal. An amplifier functions by taking power from a supply and controlling the output to match the input signal shape. In this sense, an amplifier modulates the output of the power supply based upon the properties of the input signal, an amplifier is effectively the opposite of an attenuator, while an amplifier provides gain, an attenuator provides loss. An amplifier can either be a piece of equipment or an electrical circuit contained within another device. Amplification is fundamental to modern electronics, and amplifiers are used in almost all electronic equipment. Amplifiers can be categorized in different ways, another is which quantity, voltage or current is being amplified, amplifiers can be divided into voltage amplifiers, current amplifiers, transconductance amplifiers, and transresistance amplifiers. A further distinction is whether the output is a linear or nonlinear representation of the input, amplifiers can also be categorized by their physical placement in the signal chain. The first practical device that could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest. Vacuum tubes were used in almost all amplifiers until the 1960s–1970s when the transistor, invented in 1947, today most amplifiers use transistors, but vacuum tubes continue to be used in some applications. Before the invention of electronic amplifiers, mechanically coupled carbon microphones were used as amplifiers in telephone repeaters. After the turn of the century it was found that negative resistance mercury lamps could amplify, the first practical electronic device that could amplify was the Audion vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. The terms amplifier and amplification were first used for this new capability around 1915 when triodes became widespread, the amplifying vacuum tube revolutionized electrical technology, creating the new field of electronics, the technology of active electrical devices. It made possible long distance lines, public address systems, radio broadcasting, talking motion pictures, practical audio recording, radar, television. For 50 years virtually all electronic devices used vacuum tubes. Early tube amplifiers often had positive feedback, which could increase gain but also make the amplifier unstable, much of the mathematical theory of amplifiers was developed at Bell Telephone Laboratories during the 1920s to 1940s. Other advances in the theory of amplification were made by Harry Nyquist, the vacuum tube was the only amplifying device for 40 years, and dominated electronics until 1947, when the first transistor, the BJT, was invented. Today most amplifiers use transistors, but vacuum tubes are used in some high power applications such as radio transmitters. All amplifiers have gain, a factor that relates the magnitude of some property of the output signal to a property of the input signal
7.
Radio receiver
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In radio communications, a radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna, the antenna intercepts radio waves and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The information produced by the receiver may be in the form of sound, a radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar form of radio receiver is a broadcast receiver, often just called a radio, the sound is produced either by a loudspeaker in the radio or an earphone which plugs into a jack on the radio. The radio requires electric power, provided either by batteries inside the radio or a cord which plugs into an electric outlet. All radios have a control to adjust the loudness of the audio. The frequency of radio stations is usually listed prominently in their advertising, in order to select a particular station to receive, the radio is adjusted to the frequency of the desired transmitter. In some radios this is done by the user turning a tuning knob until the station is heard in the radios loudspeaker. In most countries radio broadcasting is permitted using two different methods of modulation, that is, methods of adding the signal to the radio wave, AM and FM. In amplitude modulation the strength of the signal is varied by the audio signal. AM broadcasting is permitted on AM broadcast bands between 148 and 283 kHz in the low range and 526 and 1706 kHz in the medium frequency range of the radio spectrum. In frequency modulation the frequency of the signal is varied slightly by the audio signal. FM broadcasting is permitted in the FM broadcast bands between about 65 and 108 MHz in the high frequency range. The exact frequency ranges vary somewhat in different countries, radios sold in each receive the correct frequency range for that country. Most broadcast radios, called AM/FM radios, can receive both AM and FM bands, and have a switch to select which band to receive. Limited AM broadcasting is permitted in parts of the high frequency band called the shortwave band. Shortwave listening requires a receiver that can receive these bands, called a shortwave receiver, at these frequencies, radio waves transmitted into the sky can reflect from a layer in the atmosphere called the ionosphere, returning to earth at transcontinental distances. So shortwaves are used for long distance international broadcasting, often by governmental public service broadcasting organizations like the BBC, due to their lower frequency, AM radio stations can often be received at longer distances than FM stations, at hundreds of miles
8.
Electronic oscillator
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An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave. Oscillators convert direct current from a supply to an alternating current signal. They are widely used in electronic devices. Oscillators are often characterized by the frequency of their output signal and this term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator. An audio oscillator produces frequencies in the range, about 16 Hz to 20 kHz. An RF oscillator produces signals in the frequency range of about 100 kHz to 100 GHz. Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters, there are two main types of electronic oscillator, the linear or harmonic oscillator and the nonlinear or relaxation oscillator. The harmonic, or linear, oscillator produces a sinusoidal output, when the power supply to the amplifier is first switched on, electronic noise in the circuit provides a non-zero signal to get oscillations started. The noise travels around the loop and is amplified and filtered until very quickly it converges on a wave at a single frequency. RC oscillators are used to generate lower frequencies, for example in the audio range. Common types of RC oscillator circuits are the phase shift oscillator, in an LC oscillator circuit, the filter is a tuned circuit consisting of an inductor and capacitor connected together. Charge flows back and forth between the plates through the inductor, so the tuned circuit can store electrical energy oscillating at its resonant frequency. There are small losses in the circuit, but the amplifier compensates for those losses and supplies the power for the output signal. Typical LC oscillator circuits are the Hartley, Colpitts and Clapp circuits, in a crystal oscillator circuit the filter is a piezoelectric crystal. The crystal mechanically vibrates as a resonator, and its frequency of vibration determines the oscillation frequency, crystals have very high Q-factor and also better temperature stability than tuned circuits, so crystal oscillators have much better frequency stability than LC or RC oscillators. Crystal oscillators are the most common type of linear oscillator, used to stabilize the frequency of most radio transmitters, crystal oscillators often use the same circuits as LC oscillators, with the crystal replacing the tuned circuit, the Pierce oscillator circuit is also commonly used. Quartz crystals are generally limited to frequencies of 30 MHz or below, other types of resonator, dielectric resonators and surface acoustic wave devices, are used to control higher frequency oscillators, up into the microwave range. For example, SAW oscillators are used to generate the signal in cell phones
9.
Semiconductor
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Semiconductors are crystalline or amorphous solids with distinct electrical characteristics. They are of high electrical resistance — higher than typical resistance materials and their resistance decreases as their temperature increases, which is behavior opposite to that of a metal. The behavior of charge carriers which include electrons, ions and electron holes at these junctions is the basis of diodes, transistors and all modern electronics. Semiconductor devices can display a range of properties such as passing current more easily in one direction than the other, showing variable resistance. The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of carriers in a crystal lattice. Doping greatly increases the number of carriers within the crystal. When a doped semiconductor contains mostly free holes it is called p-type, the semiconductor materials used in electronic devices are doped under precise conditions to control the concentration and regions of p- and n-type dopants. A single semiconductor crystal can have many p- and n-type regions, although some pure elements and many compounds display semiconductor properties, silicon, germanium, and compounds of gallium are the most widely used in electronic devices. Elements near the so-called metalloid staircase, where the metalloids are located on the table, are usually used as semiconductors. Some of the properties of materials were observed throughout the mid 19th. The first practical application of semiconductors in electronics was the 1904 development of the Cats-whisker detector, developments in quantum physics in turn allowed the development of the transistor in 1947 and the integrated circuit in 1958. There are several developed techniques that allow semiconducting materials to behave like conducting materials and these modifications have two outcomes, n-type and p-type. These refer to the excess or shortage of electrons, respectively, an unbalanced number of electrons would cause a current to flow through the material. Heterojunctions Heterojunctions occur when two differently doped semiconducting materials are joined together, for example, a configuration could consist of p-doped and n-doped germanium. This results in an exchange of electrons and holes between the differently doped semiconducting materials, the n-doped germanium would have an excess of electrons, and the p-doped germanium would have an excess of holes. The transfer occurs until equilibrium is reached by a process called recombination, a product of this process is charged ions, which result in an electric field. Excited Electrons A difference in electric potential on a material would cause it to leave thermal equilibrium. This introduces electrons and holes to the system, which interact via a process called ambipolar diffusion, whenever thermal equilibrium is disturbed in a semiconducting material, the amount of holes and electrons changes
10.
Integrated circuit
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An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material, normally silicon. The ICs mass production capability, reliability and building-block approach to circuit design ensured the rapid adoption of standardized ICs in place of using discrete transistors. ICs are now used in all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other home appliances are now inextricable parts of the structure of modern societies, made possible by the small size. These advances, roughly following Moores law, allow a computer chip of 2016 to have millions of times the capacity, ICs have two main advantages over discrete circuits, cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography rather than being constructed one transistor at a time, furthermore, packaged ICs use much less material than discrete circuits. Performance is high because the ICs components switch quickly and consume little power because of their small size, the main disadvantage of ICs is the high cost to design them and fabricate the required photomasks. This high initial cost means ICs are only practical when high production volumes are anticipated, Circuits meeting this definition can be constructed using many different technologies, including thin-film transistor, thick film technology, or hybrid integrated circuit. However, in general usage integrated circuit has come to refer to the single-piece circuit construction originally known as a integrated circuit. Jacobi disclosed small and cheap hearing aids as typical industrial applications of his patent, an immediate commercial use of his patent has not been reported. The idea of the circuit was conceived by Geoffrey Dummer. Dummer presented the idea to the public at the Symposium on Progress in Quality Electronic Components in Washington and he gave many symposia publicly to propagate his ideas, and unsuccessfully attempted to build such a circuit in 1956. A precursor idea to the IC was to create small ceramic squares, Components could then be integrated and wired into a bidimensional or tridimensional compact grid. This idea, which seemed very promising in 1957, was proposed to the US Army by Jack Kilby, however, as the project was gaining momentum, Kilby came up with a new, revolutionary design, the IC. In his patent application of 6 February 1959, Kilby described his new device as a body of semiconductor material … wherein all the components of the circuit are completely integrated. The first customer for the new invention was the US Air Force, Kilby won the 2000 Nobel Prize in Physics for his part in the invention of the integrated circuit. His work was named an IEEE Milestone in 2009, half a year after Kilby, Robert Noyce at Fairchild Semiconductor developed his own idea of an integrated circuit that solved many practical problems Kilbys had not. Noyces design was made of silicon, whereas Kilbys chip was made of germanium, Noyce credited Kurt Lehovec of Sprague Electric for the principle of p–n junction isolation, a key concept behind the IC
11.
Hybrid integrated circuit
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If the components are on Printed Wiring Board then, according to the definition of MIL-PRF-38534, it is not considered hybrid. A PCB can be called PWB if does not contain embedded components, hybrid circuits are often encapsulated in epoxy, as shown in the photo. A hybrid circuit serves as a component on a PCB in the way as a monolithic integrated circuit. The advantage of hybrid circuits is that components which cannot be included in a monolithic IC can be used, e. g. capacitors of large value, wound components, crystals, thick film technology is often used as the interconnecting medium for hybrid integrated circuits. The use of screen printed thick film interconnect provides advantages of versatility over thin film although feature sizes may be larger, multi-layer thick film is a technique for further improvements in integration using a screen printed insulating dielectric to ensure connections between layers are made only where required. One key advantage for the designer is complete freedom in the choice of resistor value in thick film technology. Planar resistors are also printed and included in the thick film interconnect design. The composition and dimensions of resistors can be selected to provide desired values, the final resistor value is determined by design and can be adjusted by laser trimming. Once the hybrid circuit is fully populated with components, fine tuning prior to final test may be achieved by laser trimming. Thin film technology was employed in the 1960s. Ultra Electronics manufactured circuits using a Silica Glass substrate, a film of Tantalum was deposited by sputtering followed by a layer of gold by evaporation. The Gold layer was first etched following application of a photo resist to form solder compatible connection pads, resistive networks were formed, also by a photo resist and etching process. These were trimmed to a high precision by selective adonization of the film, capacitors and Semiconductors were in the form of LID soldered to the surface by selectively heating the substrate from the underside. Completed circuits were potted in a diallyl phthalate resin, several customized passive networks were made using these techniques as were some amplifiers and other specialized circuits. It is believed that some passive networks were used in the Engine Control Units manufactured by Ultra Electronics for Concorde and this technology produces a circuit that is, to some degree, three-dimensional. In the early days of telephones, separate modules containing transformers and resistors were called hybrids or hybrid coils, multi-chip module Monolithic microwave integrated circuit Solid Logic Technology MIL-PRF-38534 Printed Circuit Board
12.
Passivity (engineering)
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Passivity is a property of engineering systems, used in a variety of engineering disciplines, but most commonly found in analog electronics and control systems. A passive component, depending on field, may be either a component that consumes energy, a component that is not passive is called an active component. An electronic circuit consisting entirely of passive components is called a passive circuit, used out-of-context and without a qualifier, the term passive is ambiguous. Typically, analog designers use this term to refer to incrementally passive components and systems, systems for which the small signal model is not passive are sometimes called locally active. Systems that can power about a time-variant unperturbed state are often called parametrically active. In control systems and circuit theory, a passive component or circuit is one that consumes energy. Circuit designers will sometimes refer to this class of components as dissipative, while many books give definitions for passivity, many of these contain subtle errors in how initial conditions are treated. Below is a correct, formal definition, taken from Wyatt et al, a system is considered passive if EA is finite for all initial states x. Otherwise, the system is considered active, roughly speaking, the inner product ⟨ v, i ⟩ is the instantaneous power, and EA is the upper bound on the integral of the instantaneous power. This upper bound is the energy in the system for the particular initial condition x. If, for all initial states of the system, the energy available is finite. In circuit design, informally, passive components refer to ones that are not capable of power gain, under this definition, passive components include capacitors, inductors, resistors, diodes, transformers, voltage sources, and current sources. They exclude devices like transistors, vacuum tubes, relays, tunnel diodes, formally, for a memoryless two-terminal element, this means that the current–voltage characteristic is monotonically increasing. For this reason, control systems and circuit network theorists refer to these devices as locally passive, incrementally passive, increasing, monotone increasing, or monotonic. This term is used colloquially in a number of contexts, A passive USB to PS/2 adapter consists of wires. An active USB to PS/2 adapter consists of logic to translate signals A passive mixer consists of just resistors, in audio work one can also find both passive and active converters between balanced and unbalanced lines. In some very informal settings, passivity may refer to the simplicity of the device, here, devices like diodes would be considered active, and only very simple devices like capacitors, inductors, and resistors are considered passive. In some cases, the linear element may be a more appropriate term than passive device
13.
Battery (electricity)
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An electric battery is a device consisting of one or more electrochemical cells with external connections provided to power electrical devices such as flashlights, smartphones, and electric cars. When a battery is supplying power, its positive terminal is the cathode. The terminal marked negative is the source of electrons that when connected to a circuit will flow. It is the movement of ions within the battery which allows current to flow out of the battery to perform work. Historically the term specifically referred to a device composed of multiple cells. Primary batteries are used once and discarded, the materials are irreversibly changed during discharge. Common examples are the battery used for flashlights and a multitude of portable electronic devices. Secondary batteries can be discharged and recharged multiple times using mains power from a wall socket, examples include the lead-acid batteries used in vehicles and lithium-ion batteries used for portable electronics such as laptops and smartphones. According to a 2005 estimate, the battery industry generates US$48 billion in sales each year. Batteries have much lower energy than common fuels such as gasoline. This is somewhat offset by the efficiency of electric motors in producing mechanical work. The usage of battery to describe a group of electrical devices dates to Benjamin Franklin, alessandro Volta built and described the first electrochemical battery, the voltaic pile, in 1800. This was a stack of copper and zinc plates, separated by brine-soaked paper disks, Volta did not understand that the voltage was due to chemical reactions. Although early batteries were of value for experimental purposes, in practice their voltages fluctuated. It consisted of a pot filled with a copper sulfate solution, in which was immersed an unglazed earthenware container filled with sulfuric acid. These wet cells used liquid electrolytes, which were prone to leakage and spillage if not handled correctly, many used glass jars to hold their components, which made them fragile and potentially dangerous. These characteristics made wet cells unsuitable for portable appliances, near the end of the nineteenth century, the invention of dry cell batteries, which replaced the liquid electrolyte with a paste, made portable electrical devices practical. Batteries convert chemical energy directly to electrical energy, a battery consists of some number of voltaic cells
14.
Electronic engineering
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The discipline typically also designs passive electrical components, usually based on printed circuit boards. The Institute of Electrical and Electronics Engineers is one of the most important, Electronics is a subfield within the wider electrical engineering academic subject. An academic degree with a major in engineering can be acquired from some universities. The term electrical engineer is used in the academic world to include electronic engineers. The term power engineering is used as a descriptor in that industry, Electronic engineering as a profession sprang from technological improvements in the telegraph industry in the late 19th century and the radio and the telephone industries in the early 20th century. People were attracted to radio by the fascination it inspired, first in receiving. Many who went into broadcasting in the 1920s were only amateurs in the period before World War I, in the interwar years, the subject was known as radio engineering and it was only in the late 1950s that the term electronic engineering started to emerge. The tuner circuit, which allows the user of a radio to filter out all, in designing an integrated circuit, electronics engineers first construct circuit schematics that specify the electrical components and describe the interconnections between them. When completed, VLSI engineers convert the schematics into actual layouts, the conversion from schematics to layouts can be done by software but very often requires human fine-tuning to decrease space and power consumption. Once the layout is complete, it can be sent to a plant for manufacturing. Today, printed circuit boards are found in most electronic devices including televisions, computers, signal processing deals with the analysis and manipulation of signals. For analog signals, signal processing may involve the amplification and filtering of signals for audio equipment or the modulation and demodulation of signals for telecommunications. For digital signals, signal processing may involve the compression, error checking, telecommunications engineering deals with the transmission of information across a channel such as a co-axial cable, optical fiber or free space. Transmissions across free space require information to be encoded in a wave in order to shift the information to a carrier frequency suitable for transmission. Popular analog modulation techniques include amplitude modulation and frequency modulation, the choice of modulation affects the cost and performance of a system and these two factors must be balanced carefully by the engineer. Once the transmission characteristics of a system are determined, telecommunication engineers design the transmitters and receivers needed for such systems and these two are sometimes combined to form a two-way communication device known as a transceiver. A key consideration in the design of transmitters is their consumption as this is closely related to their signal strength. If the signal strength of a transmitter is insufficient the signals information will be corrupted by noise, control engineering has a wide range of applications from the flight and propulsion systems of commercial airplanes to the cruise control present in many modern cars
15.
Network analysis (electrical circuits)
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A network, in the context of electronics, is a collection of interconnected components. Network analysis is the process of finding the voltages across, There are many different techniques for calculating these values. However, for the most part, the applied technique assumes that the components of the network are all linear, the methods described in this article are only applicable to linear network analysis, except where explicitly stated. A useful procedure in network analysis is to simplify the network by reducing the number of components and this can be done by replacing the actual components with other notional components that have the same effect. A particular technique might directly reduce the number of components, for instance by combining impedances in series, on the other hand, it might merely change the form into one in which the components can be reduced in a later operation. A resistive circuit is a circuit containing only resistors, ideal current sources, if the sources are constant sources, the result is a DC circuit. Analysis of a circuit consists of solving for the voltages and currents present in the circuit, the solution principles outlined here also apply to phasor analysis of AC circuits. If V2 = V1 implies I2 = I1 for all values of V1, then with respect to terminals ab and xy, circuit 1, the above is a sufficient definition for a one-port network. For more than one port, then it must be defined that the currents, for instance, star and delta networks are effectively three port networks and hence require three simultaneous equations to fully specify their equivalence. Any two terminal network of impedances can eventually be reduced to a single impedance by successive applications of impedances in series or impedances in parallel, impedances in series, Z e q = Z1 + Z2 + ⋯ + Z n. Impedances in parallel,1 Z e q =1 Z1 +1 Z2 + ⋯ +1 Z n, the above simplified for only two impedances in parallel, Z e q = Z1 Z2 Z1 + Z2. A network of impedances with more than two terminals cannot be reduced to an impedance equivalent circuit. An n-terminal network can, at best, be reduced to n impedances, for a three terminal network, the three impedances can be expressed as a three node delta network or four node star network. These two networks are equivalent and the transformations between them are given below, a general network with an arbitrary number of nodes cannot be reduced to the minimum number of impedances using only series and parallel combinations. In general, Y-Δ and Δ-Y transformations must also be used, for some networks the extension of Y-Δ to star-polygon transformations may also be required. For equivalence, the impedances between any pair of terminals must be the same for both networks, resulting in a set of three simultaneous equations, the equations below are expressed as resistances but apply equally to the general case with impedances. Any node connected by N resistors to nodes 1, N can be replaced by resistors interconnecting the remaining N nodes. A generator with an internal impedance can be represented as either an ideal voltage generator or a current generator plus the impedance
16.
Signal
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A signal as referred to in communication systems, signal processing, and electrical engineering is a function that conveys information about the behavior or attributes of some phenomenon. The IEEE Transactions on Signal Processing states that the signal includes audio, video, speech, image, communication, geophysical, sonar, radar. Typically, signals are provided by a sensor, and often the form of a signal is converted to another form of energy using a transducer. For example, a microphone converts a signal to a voltage waveform. The formal study of the content of signals is the field of information theory. The information in a signal is accompanied by noise. The term noise usually means an undesirable random disturbance, but is extended to include unwanted signals conflicting with the desired signal. The prevention of noise is covered in part under the heading of signal integrity, the separation of desired signals from a background is the field of signal recovery, one branch of which is estimation theory, a probabilistic approach to suppressing random disturbances. Engineering disciplines such as electrical engineering have led the way in the design, study, and implementation of systems involving transmission, storage, definitions specific to sub-fields are common. For example, in theory, a signal is a codified message, that is. In the context of signal processing, arbitrary binary data streams are not considered as signals, in a communication system, a transmitter encodes a message to a signal, which is carried to a receiver by the communications channel. For example, the words Mary had a little lamb might be the message spoken into a telephone, the telephone transmitter converts the sounds into an electrical voltage signal. The signal is transmitted to the telephone by wires, at the receiver it is reconverted into sounds. In telephone networks, signalling, for example common-channel signaling, refers to number and other digital control information rather than the actual voice signal. Signals can be categorized in various ways, the most common distinction is between discrete and continuous spaces that the functions are defined over, for example discrete and continuous time domains. Discrete-time signals are often referred to as series in other fields. Continuous-time signals are often referred to as continuous signals even when the functions are not continuous. A second important distinction is between discrete-valued and continuous-valued, particularly in digital signal processing a digital signal is sometimes defined as a sequence of discrete values, that may or may not be derived from an underlying continuous-valued physical process
17.
Direct current
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Direct current is a flow of electrical charge carriers that always takes place in the same direction. The current need not always have the magnitude, but if it is to be defined as dc. This contrasts with alternating current which varies the direction of flow, sources of direct current include power supplies, electrochemical cells and batteries, and photovoltaic cells and panels. The intensity, or amplitude, of a direct current might fluctuate with time, in some such cases the dc has an ac component superimposed on it. An example of this is the output of a cell that receives a modulated light communications signal. A source of dc is sometimes called a dc generator, batteries and various other sources of dc produce a constant voltage. This is called pure dc and can be represented by a straight, the peak and effective values are the same. The peak to peak value is zero because the instantaneous amplitude never changes, in some instances the value of a dc voltage pulsates or oscillates rapidly with time, in a manner similar to the changes in an ac wave. The unfiltered output of a wave or a full wave rectifier. In 1820, Hans Christian Orsted discovered that electrical current creates a magnetic field and this discovery made scientists relate magnetism to the electric phenomena. In 1879, Thomas Edison invented the light bulb. He improved a 50-year-old idea using lower current electricity, a vacuum inside the globe and a small carbonized filament. At that time, the idea of lightning was not new. Edison not only invented an incandescent electric light, but an electric lighting system contained all the necessary elements to make the incandescent light safe, economical. Prior to 1879, direct current electricity had been used in lighting for the outdoors and it was in the 1880s when the modern electric utility industry began. It was an evolution from street lighting systems and from gas and it was located in Lower Manhattan, on Pearl Street. This station provided light and electricity to customers in a one square mile range, the station was called Thomas Edisons Pearl Street Electricity Generating Station. This station introduced four elements of an electric utility system, Efficient distribution, competitive price, reliable central generation
18.
Transistor
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A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit, a voltage or current applied to one pair of the transistors terminals controls the current through another pair of terminals. Because the controlled power can be higher than the controlling power, today, some transistors are packaged individually, but many more are found embedded in integrated circuits. The transistor is the building block of modern electronic devices. Julius Edgar Lilienfeld patented a field-effect transistor in 1926 but it was not possible to construct a working device at that time. The first practically implemented device was a point-contact transistor invented in 1947 by American physicists John Bardeen, Walter Brattain, the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics, and Bardeen, Brattain, the thermionic triode, a vacuum tube invented in 1907, enabled amplified radio technology and long-distance telephony. The triode, however, was a device that consumed a substantial amount of power. Physicist Julius Edgar Lilienfeld filed a patent for a transistor in Canada in 1925. Lilienfeld also filed patents in the United States in 1926 and 1928. However, Lilienfeld did not publish any research articles about his devices nor did his patents cite any examples of a working prototype. In 1934, German inventor Oskar Heil patented a device in Europe. Solid State Physics Group leader William Shockley saw the potential in this, the term transistor was coined by John R. Pierce as a contraction of the term transresistance. Instead, what Bardeen, Brattain, and Shockley invented in 1947 was the first point-contact transistor, Mataré had previous experience in developing crystal rectifiers from silicon and germanium in the German radar effort during World War II. Using this knowledge, he began researching the phenomenon of interference in 1947, realizing that Bell Labs scientists had already invented the transistor before them, the company rushed to get its transistron into production for amplified use in Frances telephone network. The first bipolar junction transistors were invented by Bell labs William Shockley, on April 12,1950, Bell Labs chemists Gordon Teal and Morgan Sparks had successfully produced a working bipolar NPN junction amplifying germanium transistor. Bell Labs had made this new sandwich transistor discovery announcement, in a release on July 4,1951. The first high-frequency transistor was the surface-barrier germanium transistor developed by Philco in 1953 and these were made by etching depressions into an N-type germanium base from both sides with jets of Indium sulfate until it was a few ten-thousandths of an inch thick
19.
Vacuum tube
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In electronics, a vacuum tube, an electron tube, or just a tube, or valve, is a device that controls electric current between electrodes in an evacuated container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament and this type is called a thermionic tube or thermionic valve. A phototube, however, achieves electron emission through the photoelectric effect, the simplest vacuum tube, the diode, contains only a heater, a heated electron-emitting cathode, and a plate. Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the travel through the tube and are collected by the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids, Tubes with grids can be used for many purposes, including amplification, rectification, switching, oscillation, and display. In the 1940s the invention of devices made it possible to produce solid-state devices, which are smaller, more efficient, more reliable, more durable. Hence, from the mid-1950s solid-state devices such as transistors gradually replaced tubes, the cathode-ray tube remained the basis for televisions and video monitors until superseded in the 21st century. However, there are still a few applications for which tubes are preferred to semiconductors, for example, the used in microwave ovens. One classification of vacuum tubes is by the number of active electrodes, a device with two active elements is a diode, usually used for rectification. Devices with three elements are used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have additional functions made possible by the additional controllable electrodes. X-ray tubes are vacuum tubes. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission, since these sorts of vacuum tubes have functions other than electronic amplification and rectification they are described in their own articles. A vacuum tube consists of two or more electrodes in a vacuum inside an airtight enclosure, most tubes have glass envelopes, though ceramic and metal envelopes have been used. The electrodes are attached to leads which pass through the envelope via an airtight seal, Tubes were a frequent cause of failure in electronic equipment, and consumers were expected to be able to replace tubes themselves. In addition to the terminals, some tubes had an electrode terminating at a top cap. The principal reason for doing this was to avoid leakage resistance through the tube base, the bases were commonly made with phenolic insulation which performs poorly as an insulator in humid conditions. There was even a design that had two top cap connections
20.
Tunnel diode
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It was invented in August 1957 by Leo Esaki, Yuriko Kurose and Takashi Suzuki when they were working at Tokyo Tsushin Kogyo, now known as Sony. In 1973 Esaki received the Nobel Prize in Physics, jointly with Brian Josephson, robert Noyce independently came up with the idea of a tunnel diode while working for William Shockley, but was discouraged from pursuing it. These diodes have a heavily doped p–n junction that is about 10 nm wide, the heavy doping results in a broken band gap, where conduction band electron states on the n-side are more or less aligned with valence band hole states on the p-side. Tunnel diodes were first manufactured by Sony in 1957 followed by General Electric and other companies from about 1960, tunnel diodes are usually made from germanium, but can also be made from gallium arsenide and silicon materials. They are used in converters and detectors. They have negative resistance in part of their operating range, and therefore are also used as oscillators, amplifiers. In 1977, the Intelsat V satellite receiver used a tunnel diode amplifier front-end in the 14 to 15.5 GHz frequency band. Such amplifiers were considered state-of-the-art, with performance at high frequencies than any transistor-based front end. The highest frequency room-temperature solid-state oscillators are based on the resonant-tunneling diode, there is another type of tunnel diode called a metal–insulator–metal diode, but its present application appears to be limited to research environments due to inherent sensitivities. There is also a metal–insulator–insulator–metal MIIM diode which has an additional insulator layer, the additional layer allows step tunneling for precise diode control. As voltage increases further, these become increasingly misaligned and the current drops. This is called negative resistance because current decreases with increasing voltage, the most important operating region for a tunnel diode is the negative resistance region. Its graph is different from normal p-n junction diode, when used in the reverse direction, tunnel diodes are called back diodes and can act as fast rectifiers with zero offset voltage and extreme linearity for power signals. Under reverse bias, filled states on the p-side become increasingly aligned with empty states on the n-side, in a conventional semiconductor diode, conduction takes place while the p–n junction is forward biased and blocks current flow when the junction is reverse biased. This occurs up to a point known as the breakdown voltage at which point conduction begins. In the tunnel diode, the dopant concentrations in the p and n layers are increased to a such that the reverse breakdown voltage becomes zero. This negative resistance region can be exploited in a solid version of the dynatron oscillator which normally uses a tetrode thermionic valve. The tunnel diode showed great promise as an oscillator and high-frequency threshold device since it operated at frequencies far greater than the tetrode could, well into the microwave bands
21.
Two-port network
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A two-port network is an electrical network or device with two pairs of terminals to connect to external circuits. The ports constitute interfaces where the network connects to other networks, in a two-port network, often port 1 is considered the input port and port 2 is considered the output port. The two-port network model is used in circuit analysis techniques to isolate portions of larger circuits. A two-port network is regarded as a box with its properties specified by a matrix of numbers. This allows the response of the network to signals applied to the ports to be calculated easily, without solving for all the internal voltages and it also allows similar circuits or devices to be compared easily. For example, transistors are often regarded as two-ports, characterized by their h-parameters which are listed by the manufacturer, any linear circuit with four terminals can be regarded as a two-port network provided that it does not contain an independent source and satisfies the port conditions. Examples of circuits analyzed as two-ports are filters, matching networks, transmission lines, transformers, the analysis of passive two-port networks is an outgrowth of reciprocity theorems first derived by Lorentz. In two-port mathematical models, the network is described by a 2 by 2 square matrix of complex numbers, the common models that are used are referred to as z-parameters, y-parameters, h-parameters, g-parameters, and ABCD-parameters, each described individually below. The difference between the various models lies in which of these variables are regarded as the independent variables and these current and voltage variables are most useful at low-to-moderate frequencies. At high frequencies, the use of power and energy variables is more appropriate, there are certain properties of two-ports that frequently occur in practical networks and can be used to greatly simplify the analysis. Exchanging voltage and current results in an equivalent definition of reciprocity, a network that consists entirely of linear passive components is usually reciprocal, a notable exception being passive circulators and isolators that contain magnetized materials. In general, it not be reciprocal if it contains active components such as generators or transistors. Symmetrical networks A network is symmetrical if its input impedance is equal to its output impedance, most often, but not necessarily, symmetrical networks are also physically symmetrical. Sometimes also antimetrical networks are of interest and these are networks where the input and output impedances are the duals of each other. Lossless network A lossless network is one which contains no resistors or other dissipative elements, for reciprocal networks z 12 = z 21. For symmetrical networks z 11 = z 22, for reciprocal lossless networks all the z m n are purely imaginary. Figure 3 shows a current mirror with emitter resistors to increase its output resistance. Transistor Q1 is diode connected, which is to say its collector-base voltage is zero, Figure 4 shows the small-signal circuit equivalent to Figure 3
22.
Diode
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In electronics, a diode is a two-terminal electronic component that conducts primarily in one direction, it has low resistance to the current in one direction, and high resistance in the other. A semiconductor diode, the most common today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. A vacuum tube diode has two electrodes, a plate and a heated cathode, semiconductor diodes were the first semiconductor electronic devices. The discovery of crystals rectifying abilities was made by German physicist Ferdinand Braun in 1874, the first semiconductor diodes, called cats whisker diodes, developed around 1906, were made of mineral crystals such as galena. Today, most diodes are made of silicon, but other such as selenium and germanium are sometimes used. The most common function of a diode is to allow a current to pass in one direction. Thus, the diode can be viewed as a version of a check valve. However, diodes can have complicated behavior than this simple on–off action. Semiconductor diodes begin conducting electricity only if a threshold voltage or cut-in voltage is present in the forward direction. The voltage drop across a forward-biased diode varies only a little with the current, and is a function of temperature, a semiconductor diodes current–voltage characteristic can be tailored by selecting the semiconductor materials and the doping impurities introduced into the materials during manufacture. These techniques are used to create special-purpose diodes that perform different functions. Tunnel, Gunn and IMPATT diodes exhibit negative resistance, which is useful in microwave, Diodes, both vacuum and semiconductor, can be used as shot-noise generators. Thermionic diodes and solid state diodes were developed separately, at approximately the time, in the early 1900s. Until the 1950s vacuum tube diodes were used frequently in radios because the early point-contact type semiconductor diodes were less stable. In 1873, Frederick Guthrie discovered the principle of operation of thermionic diodes. Guthrie discovered that a positively charged electroscope could be discharged by bringing a piece of white-hot metal close to it. The same did not apply to a negatively charged electroscope, indicating that the current flow was possible in one direction. Thomas Edison independently rediscovered the principle on February 13,1880, at the time, Edison was investigating why the filaments of his carbon-filament light bulbs nearly always burned out at the positive-connected end
23.
Rectifier
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A rectifier is an electrical device that converts alternating current, which periodically reverses direction, to direct current, which flows in only one direction. The process is known as rectification, historically, even synchronous electromechanical switches and motors have been used. Early radio receivers, called crystal radios, used a cats whisker of fine wire pressing on a crystal of galena to serve as a rectifier or crystal detector. Rectifiers have many uses, but are found serving as components of DC power supplies. Rectification may serve in other than to generate direct current for use as a source of power. As noted, detectors of radio signals serve as rectifiers, in gas heating systems flame rectification is used to detect presence of a flame. Because of the nature of the input AC sine wave. Many applications of rectifiers, such as supplies for radio, television and computer equipment. In these applications the output of the rectifier is smoothed by a filter to produce a steady current. More complex circuitry that performs the function, converting DC to AC, is called an inverter. Before the development of semiconductor rectifiers, vacuum tube thermionic diodes. With the introduction of electronics, vacuum tube rectifiers became obsolete. For power rectification from very low to high current, semiconductor diodes of various types are widely used. Other devices that have control electrodes as well as acting as unidirectional current valves are used more than simple rectification is required—e. g. Where variable output voltage is needed, high-power rectifiers, such as those used in high-voltage direct current power transmission, employ silicon semiconductor devices of various types. These are thyristors or other controlled switching solid-state switches, which function as diodes to pass current in only one direction. Rectifier circuits may be single-phase or multi-phase, most low power rectifiers for domestic equipment are single-phase, but three-phase rectification is very important for industrial applications and for the transmission of energy as DC. Because only one half of the input waveform reaches the output, half-wave rectification requires a single diode in a single-phase supply, or three in a three-phase supply
24.
Diode bridge
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A diode bridge is an arrangement of four diodes in a bridge circuit configuration that provides the same polarity of output for either polarity of input. When used in its most common application, for conversion of an alternating current input into a current output. The essential feature of a bridge is that the polarity of the output is the same regardless of the polarity at the input. The diode bridge circuit was invented by Polish electrotechnician Karol Pollak and it was later published in Elektronische Zeitung, vol.25 in 1897 with annotation that German physicist Leo Graetz also was researching this matter at that time. Today the circuit is often referred as Graetz circuit or Graetz bridge. According to the model of current flow, current is defined to be positive when it flows through electrical conductors from the positive to the negative pole. In actuality, free electrons in a nearly always flow from the negative to the positive pole. In the vast majority of applications, however, the direction of current flow is irrelevant. Therefore, in the discussion below the model is retained. In each case, the right output remains positive and lower right output negative. Since this is whether the input is AC or DC. Prior to the availability of integrated circuits, a bridge rectifier was constructed from discrete components, the function of this capacitor, known as a reservoir capacitor is to lessen the variation in the rectified AC output voltage waveform from the bridge. There is still some variation, known as ripple, one explanation of smoothing is that the capacitor provides a low impedance path to the AC component of the output, reducing the AC voltage across, and AC current through, the resistive load. In less technical terms, any drop in the output voltage and this charge flows out as additional current through the load. Thus the change of current and voltage is reduced relative to what would occur without the capacitor. Increases of voltage correspondingly store excess charge in the capacitor, thus moderating the change in output voltage / current. The simplified circuit shown has a reputation for being dangerous, because, in some applications. If supplying a dangerous voltage, a circuit would include a reliable way to discharge the capacitor safely
25.
Schottky diode
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The Schottky diode, also known as hot carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low voltage drop and a very fast switching action. The cats-whisker detectors used in the days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes. When sufficient forward voltage is applied, a current flows in the forward direction, a silicon diode has a typical forward voltage of 600–700 mV, while the Schottkys forward voltage is 150 –450 mV. This lower forward voltage requirement allows higher switching speeds and better system efficiency, a metal–semiconductor junction is formed between a metal and a semiconductor, creating a Schottky barrier. Typical metals used are molybdenum, platinum, chromium or tungsten, the metal side acts as the anode, and n-type semiconductor acts as the cathode of the diode. This Schottky barrier results in very fast switching and low forward voltage drop. The choice of the combination of the metal and semiconductor determines the voltage of the diode. Both n- and p-type semiconductors can develop Schottky barriers, however, the p-type typically has a much lower forward voltage. With increased doping of the semiconductor, the width of the depletion region drops, below a certain width, the charge carriers can tunnel through the depletion region. At very high doping levels, the junction does not behave as a rectifier anymore, as the edges of the Schottky contact are fairly sharp, a high electric field gradient occurs around them, which limits how large the reverse breakdown voltage threshold can be. Various strategies are used, from guard rings to overlaps of metallization to spread out the field gradient, the guard rings consume valuable die area and are used primarily for larger higher-voltage diodes, while overlapping metallization is employed primarily with smaller low-voltage diodes. Schottky diodes are used as antisaturation clamps in Schottky transistors. Schottky diodes made from palladium silicide are excellent due to their forward voltage. The Schottky temperature coefficient is lower than the coefficient of the B–C junction, for power Schottky diodes, the parasitic resistances of the buried n+ layer and the epitaxial n-type layer become important. The resistance of the layer is more important than it is for a transistor. However, it serves as a distributed ballasting resistor over the area of the junction and, under usual conditions. In comparison with the power p–n diodes the Schottky diodes are less rugged, the relative advantage of the lower forward voltage of Schottky diodes is diminished at higher forward currents, where the voltage drop is dominated by the series resistance
26.
Zener diode
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A Zener diode allows current to flow from its anode to its cathode like a normal semiconductor diode, but it also permits current to flow in the reverse direction when its Zener voltage is reached. Zener diodes have a highly doped p-n junction, normal diodes will also break down with a reverse voltage but the voltage and sharpness of the knee are not as well defined as for a Zener diode. Also normal diodes are not designed to operate in the breakdown region, the device was named after Clarence Melvin Zener, who discovered the Zener effect. Zener reverse breakdown is due to quantum tunnelling caused by a high strength electric field. However, many described as Zener diodes rely instead on avalanche breakdown. Both breakdown types are used in Zener diodes with the Zener effect predominating under 5.6 V, Zener diodes are widely used in electronic equipment of all kinds and are one of the basic building blocks of electronic circuits. They are used to generate low power stabilized supply rails from a voltage and to provide reference voltages for circuits. They are also used to protect circuits from over-voltage, especially electrostatic discharge, a conventional solid-state diode allows significant current if it is reverse-biased above its reverse breakdown voltage. When the reverse breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Unless this current is limited by circuitry, the diode may be damaged due to overheating. A Zener diode exhibits almost the same properties, except the device is designed so as to have a reduced breakdown voltage. For example, a diode with a Zener breakdown voltage of 3.2 V exhibits a voltage drop of very nearly 3.2 V across a range of reverse currents. The Zener diode is therefore ideal for such as the generation of a reference voltage. Another mechanism that produces an effect is the avalanche effect as in the avalanche diode. The two types of diode are in fact constructed the same way and both effects are present in diodes of this type, in silicon diodes up to about 5.6 volts, the Zener effect is the predominant effect and shows a marked negative temperature coefficient. Above 5.6 volts, the effect becomes predominant. In a 5.6 V diode, the two occur together, and their temperature coefficients nearly cancel each other out, thus the 5.6 V diode is useful in temperature-critical applications. The forward-biased diode has a coefficient of −2 mV/°C, causing the TCs to cancel out
27.
Transient-voltage-suppression diode
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A transient-voltage-suppression diode or thyrector is an electronic component used to protect electronics from voltage spikes induced on connected wires. The device operates by shunting excess current when the voltage exceeds the avalanche breakdown potential. It is a device, suppressing all overvoltages above its breakdown voltage. It automatically resets when the overvoltage goes away, but absorbs much more of the transient energy internally than a similarly rated crowbar device, a transient-voltage-suppression diode may be either unidirectional or bidirectional. A unidirectional device operates as a rectifier in the forward direction like any other avalanche diode, the 1. 5KE series allows 1500 W of peak power, for a short time. A bidirectional transient-voltage-suppression diode can be represented by two mutually opposing avalanche diodes in series with one another and connected in parallel with the circuit to be protected, while this representation is schematically accurate, physically the devices are now manufactured as a single component. A transient-voltage-suppression diode can respond to over-voltages faster than other common over-voltage protection components such as varistors or gas discharge tubes, the actual clamping occurs in roughly one picosecond, but in a practical circuit the inductance of the wires leading to the device imposes a higher limit. This makes transient-voltage-suppression diodes useful for protection against very fast and often damaging voltage transients and these fast over-voltage transients are present on all distribution networks and can be caused by either internal or external events, such as lightning or motor arcing. Transient voltage suppressors will fail if they are subjected to voltages or conditions beyond those that the product was designed to accommodate. There are three key modes in which the TVS will fail, short, open, and degraded device, TVS diodes are sometimes referred to as transorbs or the Vishay General Semiconductor registered trademark, TransZorbs. A TVS diode is characterized by, Leakage current, the amount of current conducted when voltage applied is below the maximum reverse standoff voltage, maximum reverse standoff voltage, the voltage below which no significant conduction occurs. Breakdown voltage, the voltage at which some specified and significant conduction occurs, clamping voltage, the voltage at which the device will conduct its fully rated current. Parasitic capacitance, The nonconducting diode behaves like a capacitor, which can have an effect on high-speed signals. Parasitic inductance, Because the actual over voltage switching is so fast, amount of energy it can absorb, Because the transients are so brief, all of the energy is initially stored internally as heat, a heat sink only affects the time to cool down afterwards. Thus, a high-energy TVS must be physically large, if this capacity is too small, the over voltage will possibly destroy the device and leave the circuit unprotected. Trisil Zener diode TVS/Zener Theory and Design Considerations, ON Semiconductor,127 pages,2005, HBD854/D
28.
Varicap
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Varactors are used as voltage-controlled capacitors. They are commonly used in voltage-controlled oscillators, parametric amplifiers, voltage-controlled oscillators have many applications such as frequency modulation for FM transmitters and phase-locked loops. Phase-locked loops are used for the synthesizers that tune many radios, television sets. The varicap was developed by the Pacific Semiconductor subsidiary of the Ramo Wooldridge Corporation who received a patent for the device in June 1961, the device name was also trademarked as the Varicap by TRW Semiconductors, the successor to Pacific Semiconductors, in October 1967. This helps explain the different names for the device as it came into use, varactors are operated in a reverse-biased state, so no DC current flows through the device. The amount of reverse bias controls the thickness of the depletion zone, generally, the depletion region thickness is proportional to the square root of the applied voltage, and capacitance is inversely proportional to the depletion region thickness. Thus, the capacitance is proportional to the square root of applied voltage. All diodes exhibit this variable junction capacitance, but varactors are manufactured to exploit the effect, the figure shows an example of a cross section of a varactor with the depletion layer formed of a p–n junction. This depletion layer can also be made of a MOS or a Schottky diode and this is important in CMOS and MMIC technology. Generally the use of a diode in a circuit requires connecting it to a tuned circuit. Because a DC voltage must be applied reverse bias across the varicap to alter its capacitance, a second circuit using two back-to-back, series-connected varicap diodes is another common configuration. The second varicap effectively replaces the blocking capacitor in the first circuit, one remaining circuit, right, depicts two series connected varicaps being used in a circuit with separate DC and AC signal ground connections. The DC ground being depicted as the traditional symbol. These circuit configurations are common in television tuners and electronically tuned broadcast AM and FM receivers, as well as other communications equipment. Early varicap diodes usually required a reverse voltage range of 0–33 v to obtain capacitance range and these types were and are still extensively used in television tuners, whose high carrier frequencies require only small changes in capacitance. In time, varicap diodes were developed which exhibited very large ranges, 100–500 pF, with relatively small changes in reverse bias. Some of designs of electronic security tag readers used in retail outlets require these high capacitance varicaps in their voltage-controlled oscillators, the three leaded devices depicted at the top of the page are generally two common cathode connected varicaps in a single package. In the consumer AM/FM tuner depicted at the right, a single dual-package varicap diode adjusts both the passband of the circuit, and the local oscillator with a single varicap for each
29.
Light-emitting diode
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A light-emitting diode is a two-lead semiconductor light source. It is a p–n junction diode, which emits light when activated, when a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light is determined by the band gap of the semiconductor. LEDs are typically small and integrated optical components may be used to shape the radiation pattern, appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared light. Infrared LEDs are still used as transmitting elements in remote-control circuits. The first visible-light LEDs were also of low intensity and limited to red, modern LEDs are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness. Early LEDs were often used as indicator lamps for electronic devices and they were soon packaged into numeric readouts in the form of seven-segment displays and were commonly seen in digital clocks. Recent developments in LEDs permit them to be used in environmental, LEDs have allowed new displays and sensors to be developed, while their high switching rates are also used in advanced communications technology. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are now used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, camera flashes, as of 2017, LED lights home room lighting are as cheap or cheaper than compact fluorescent lamp sources of comparable output. They are also more energy efficient and, arguably, have fewer environmental concerns linked to their disposal. Electroluminescence as a phenomenon was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide, russian inventor Oleg Losev reported creation of the first LED in 1927. His research was distributed in Soviet, German and British scientific journals, rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide and other semiconductor alloys in 1955. Braunstein observed infrared emission generated by simple diode structures using gallium antimonide, GaAs, indium phosphide, in 1957, Braunstein further demonstrated that the rudimentary devices could be used for non-radio communication across a short distance. As noted by Kroemer Braunstein …had set up a simple optical communications link, the emitted light was detected by a PbS diode some distance away. This signal was fed into an amplifier and played back by a loudspeaker. Intercepting the beam stopped the music and we had a great deal of fun playing with this setup. This setup presaged the use of LEDs for optical communication applications, by October 1961, they had demonstrated efficient light emission and signal coupling between a GaAs p-n junction light emitter and an electrically-isolated semiconductor photodetector
30.
Photodiode
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A photodiode is a semiconductor device that converts light into current. The current is generated when photons are absorbed in the photodiode, a small amount of current is also produced when no light is present. Photodiodes may contain optical filters, built-in lenses, and may have large or small surface areas, photodiodes usually have a slower response time as their surface area increases. The common, traditional solar cell used to generate solar power is a large area photodiode. Many diodes designed for use specifically as a photodiode use a PIN junction rather than a p–n junction, a photodiode is designed to operate in reverse bias. A photodiode is a p–n junction or PIN structure, when a photon of sufficient energy strikes the diode, it creates an electron-hole pair. This mechanism is known as the inner photoelectric effect. If the absorption occurs in the depletion region, or one diffusion length away from it. Thus holes move toward the anode, and electrons toward the cathode, the total current through the photodiode is the sum of the dark current and the photocurrent, so the dark current must be minimized to maximize the sensitivity of the device. When used in zero bias or photovoltaic mode, the flow of photocurrent out of the device is restricted and this mode exploits the photovoltaic effect, which is the basis for solar cells – a traditional solar cell is just a large area photodiode. In this mode the diode is reverse biased. This reduces the time because the additional reverse bias increases the width of the depletion layer. The reverse bias increases the dark current without much change in the photocurrent. For a given distribution, the photocurrent is linearly proportional to the illuminance. Although this mode is faster, the photoconductive mode tends to more electronic noise. The leakage current of a good PIN diode is so low that the Johnson–Nyquist noise of the resistance in a typical circuit often dominates. Avalanche photodiodes are photodiodes with structure optimized for operating with high reverse bias and this allows each photo-generated carrier to be multiplied by avalanche breakdown, resulting in internal gain within the photodiode, which increases the effective responsivity of the device. A phototransistor is a light-sensitive transistor, a common type of phototransistor, called a photobipolar transistor, is in essence a bipolar transistor encased in a transparent case so that light can reach the base–collector junction
31.
Avalanche photodiode
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An avalanche photodiode is a highly sensitive semiconductor electronic device that exploits the photoelectric effect to convert light to electricity. APDs can be thought of as photodetectors that provide a built-in first stage of gain through avalanche multiplication, from a functional standpoint, they can be regarded as the semiconductor analog to photomultipliers. By applying a reverse bias voltage, APDs show an internal current gain effect due to impact ionization. In general, the higher the voltage, the higher the gain. This coefficient has a dependence on the applied electric field strength, temperature. Since APD gain varies strongly with the reverse bias and temperature. Avalanche photodiodes therefore are more compared to other semiconductor photodiodes. If very high gain is needed, certain APDs can be operated with a voltage above the APDs breakdown voltage. In this case, the APD needs to have its current limited. Active and passive current-quenching techniques have been used for this purpose, APDs that operate in this high-gain regime are in Geiger mode. This mode is useful for single-photon detection, provided that the dark count event rate is sufficiently low. A typical application for APDs is laser rangefinders and long-range fiber-optic telecommunication, new applications include positron emission tomography and particle physics. APD arrays are becoming commercially available, APD applicability and usefulness depends on many parameters. Electronic dark-noise components are series and parallel noise, another noise source is the excess noise factor, ENF. It describes the noise that is inherent with the stochastic APD multiplication process. This is not to be confused with the Fano noise, which describes the fluctuation of the electric charge collected in the APD. In principle, any material can be used as a multiplication region, Silicon will detect in the visible and near infrared. Germanium will detect infrared out to a wavelength of 1.7 µm, InGaAs will detect out to longer than 1.6 µm and has less multiplication noise than Ge
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Solar cell
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A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. It is a form of cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance. Solar cells are the blocks of photovoltaic modules, otherwise known as solar panels. Solar cells are described as being photovoltaic, irrespective of whether the source is sunlight or an artificial light and they are used as a photodetector, detecting light or other electromagnetic radiation near the visible range, or measuring light intensity. The operation of a cell requires three basic attributes, The absorption of light, generating either electron-hole pairs or excitons. The separation of carriers of opposite types. The separate extraction of those carriers to an external circuit, in contrast, a solar thermal collector supplies heat by absorbing sunlight, for the purpose of either direct heating or indirect electrical power generation from heat. A photoelectrolytic cell, on the hand, refers either to a type of photovoltaic cell. Assemblies of solar cells are used to make solar modules that generate power from sunlight. A solar array generates power using solar energy. Multiple solar cells in a group, all oriented in one plane. Photovoltaic modules often have a sheet of glass on the sun-facing side, Solar cells are usually connected in series and parallel circuits or series in modules, creating an additive voltage. Strings of series cells are usually handled independently and not connected in parallel, though as of 2014, individual power boxes are often supplied for each module, and are connected in parallel. Although modules can be interconnected to create an array with the desired peak DC voltage and loading current capacity, otherwise, shunt diodes can reduce shadowing power loss in arrays with series/parallel connected cells. The photovoltaic effect was demonstrated first by French physicist Edmond Becquerel. In 1839, at age 19, he built the worlds first photovoltaic cell in his fathers laboratory, willoughby Smith first described the Effect of Light on Selenium during the passage of an Electric Current in a 20 February 1873 issue of Nature. In 1883 Charles Fritts built the first solid state photovoltaic cell by coating the semiconductor selenium with a layer of gold to form the junctions. In 1888 Russian physicist Aleksandr Stoletov built the first cell based on the photoelectric effect discovered by Heinrich Hertz in 1887
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DIAC
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The DIAC is a diode that conducts electrical current only after its breakover voltage, VBO, has been reached momentarily. The term is an acronym of diode for alternating current, the diode remains in conduction until the current through it drops below a value characteristic for the device, called the holding current, IH. Below this value, the diode switches back to its high-resistance and this behavior is bidirectional, meaning typically the same for both directions of current. Most DIACs have a structure with breakover voltage of approximately 30 V. Their behavior is similar to that of a lamp, but it can be more precisely controlled. DIACs have no gate electrode, unlike some other thyristors that they are used to trigger. Some TRIACs, like Quadrac, contain a built-in DIAC in series with the TRIACs gate terminal for this purpose, DIACs are also called symmetrical trigger diodes due to the symmetry of their characteristic curve. Because DIACs are bidirectional devices, their terminals are not labeled as anode and cathode but as A1 and A2 or main terminal MT1 and MT2. A Silicon Diode for Alternating Current is a commonly used device, electrically similar to the DIAC, but having, in general. The SIDAC is another member of the thyristor family, also referred to as a SYDAC, bi-directional thyristor breakover diode, or more simply a bi-directional thyristor diode, it is technically specified as a bilateral voltage triggered switch. Its operation is similar to that of the DIAC, but SIDAC is always a five-layer device with low-voltage drop in latched conducting state, more like a voltage triggered TRIAC without a gate. In general, SIDACs have higher breakover voltages and current handling capacities than DIACs, so they can be used for switching. The operation of the SIDAC is functionally similar to that of a spark gap, the SIDAC remains nonconducting until the applied voltage meets or exceeds its rated breakover voltage. At this point, the SIDAC returns to its initial state to begin the cycle once again. Somewhat uncommon in most electronics, the SIDAC is relegated to the status of a special purpose device and these are designed to tolerate large surge currents for the suppression of overvoltage transients. In many applications this function is now served by metal oxide varistors, particularly for trapping voltage transients on the power mains
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Constant-current diode
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Constant-current diode is an electronic device that limits current to a maximum specified value for the device. It is known as current-limiting diode, current-regulating diode and these diodes consist of an n-channel JFET-transistor with the gate shorted to the source, which functions like a two-terminal current limiter or current source. They allow a current through them to rise to a certain value, unlike Zener diodes, these diodes keep the current constant instead of the voltage constant. These devices keep the current flowing through them unchanged when the voltage changes, note the negative VGS is required, as an example on the n-type junction-gate field-effect transistor 2N5457
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Thermoelectric cooling
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Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. Such an instrument is called a Peltier device, Peltier heat pump. It can be used either for heating or for cooling, although in practice the application is cooling. It can also be used as a controller that either heats or cools. This technology is far less commonly applied to refrigeration than vapor-compression refrigeration is and its main disadvantages are high cost and poor power efficiency. Many researchers and companies are trying to develop Peltier coolers that are cheap, a Peltier cooler can also be used as a thermoelectric generator. When operated as a cooler, a voltage is applied across the device, and as a result, a difference in temperature will build up between the two sides. When operated as a generator, one side of the device is heated to a greater than the other side, and as a result. However, a well-designed Peltier cooler will be a mediocre thermoelectric generator and vice versa, due to different design, Thermoelectric coolers operate by the Peltier effect. The device has two sides, and when a DC electric current flows through the device, it brings heat from one side to the other, so that one side gets cooler while the other gets hotter. The hot side is attached to a sink so that it remains at ambient temperature. In some applications, multiple coolers can be cascaded together for lower temperature, two unique semiconductors, one n-type and one p-type, are used because they need to have different electron densities. The semiconductors are placed thermally in parallel to other and electrically in series. When a voltage is applied to the ends of the two semiconductors there is a flow of DC current across the junction of the semiconductors causing a temperature difference. The side with the cooling plate absorbs heat which is moved to the other side of the device where the heat sink is. TECs are typically connected side by side and sandwiched between two ceramic plates, the cooling ability of the total unit is then proportional to the number of TECs in it. The more heat moved using a TEC, the less efficient it becomes, the amount of heat that can be absorbed is proportional to the current and time. Q = P I t where P is the Peltier Coefficient, I is the current, the Peltier Coefficient is dependent on temperature and the materials the TEC is made of
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Heat pump
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A heat pump is a device that transfers heat energy from a source of heat to a destination called a heat sink. Heat pumps are designed to move energy in the opposite direction of spontaneous heat transfer by absorbing heat from a cold space. A heat pump uses a small amount of power to accomplish the work of transferring energy from the heat source to the heat sink. While air conditioners and freezers are familiar examples of heat pumps, in this use, heat pumps generally draw heat from the cooler external air or from the ground. In heating mode, heat pumps are three to four times more effective at heating than simple electrical resistance heaters using the amount of electricity. Typically installed cost for a pump is about 20 times greater than for resistance heaters. Heat energy naturally transfers from warmer places to colder spaces, however, a heat pump can reverse this by absorbing heat from a cold space and releasing it to a warmer one. Heat is not conserved in this process and requires some amount of energy such as electricity. These heat pumps can be reversible, and work in either direction to provide heating or cooling to the internal space, heat pumps are used to transfer heat because less high-grade energy is required than is released as heat. Most of the energy for heating comes from the external environment, heat pumps use a refrigerant as an intermediate fluid to absorb heat where it vaporizes, in the evaporator, and then to release heat where the refrigerant condenses, in the condenser. The refrigerant flows through insulated pipes between the evaporator and the condenser, allowing for efficient thermal energy transfer at relatively long distances, reversible heat pumps work in either direction to provide heating or cooling to the internal space. They employ a valve to reverse the flow of refrigerant from the compressor through the condenser. In heating mode, the coil is an evaporator, while the indoor is a condenser. The refrigerant flowing from the evaporator carries the energy from outside air indoors. Vapor temperature is augmented within the pump by compressing it, the indoor coil then transfers thermal energy to the indoor air, which is then moved around the inside of the building by an air handler. Alternatively, thermal energy is transferred to water, which is used to heat the building via radiators or underfloor heating. The heated water may also be used for hot water consumption. The refrigerant is then allowed to expand, cool, and absorb heat from the temperature in the outside evaporator
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Bipolar junction transistor
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A bipolar junction transistor is a type of transistor that uses both electron and hole charge carriers. In contrast, unipolar transistors, such as transistors, only use one kind of charge carrier. For their operation, BJTs use two junctions between two types, n-type and p-type. BJTs are manufactured in two types, NPN and PNP, and are available as components, or fabricated in integrated circuits. The basic function of a BJT is to amplify current, by convention, the direction of current on diagrams is shown as the direction that a positive charge would move. However, current in many metal conductors is due to the flow of electrons which, because they carry a negative charge, on the other hand, inside a bipolar transistor, currents can be composed of both positively charged holes and negatively charged electrons. In this article, current arrows are shown in the conventional direction, the arrow on the symbol for bipolar transistors points in the direction conventional current travels. BJTs come in two types, or polarities, known as PNP and NPN based on the types of the three main terminal regions. An NPN transistor comprises two semiconductor junctions that share a thin p-doped region, and a PNP transistor comprises two semiconductor junctions that share a thin n-doped region, charge flow in a BJT is due to diffusion of charge carriers across a junction between two regions of different charge concentrations. The regions of a BJT are called emitter, collector, a discrete transistor has three leads for connection to these regions. Typically, the region is heavily doped compared to the other two layers, whereas the majority charge carrier concentrations in base and collector layers are about the same. This allows thermally excited electrons to inject from the emitter into the base region and these electrons diffuse through the base from the region of high concentration near the emitter towards the region of low concentration near the collector. The electrons in the base are called minority carriers because the base is doped p-type, in particular, the thickness of the base must be much less than the diffusion length of the electrons. The thin shared base and asymmetric collector–emitter doping are what differentiates a bipolar transistor from two separate and oppositely biased diodes connected in series, the collector–emitter current can be viewed as being controlled by the base–emitter current, or by the base–emitter voltage. These views are related by the relation of the base–emitter junction. The physical explanation for collector current is the concentration of minority carriers in the base region, due to low level injection the ambipolar transport rates is in effect determined by the excess minority carriers. Detailed transistor models of transistor action, such as the Gummel–Poon model, however, because base charge is not a signal that is visible at the terminals, the current- and voltage-control views are generally used in circuit design and analysis. In analog circuit design, the view is sometimes used because it is approximately linear
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Darlington transistor
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Integrated Darlington pairs come packaged singly in transistor-like packages or as an array of devices in an integrated circuit. The Darlington configuration was invented by Bell Laboratories engineer Sidney Darlington in 1953 and he patented the invention of having two or three transistors on a single chip sharing a collector. A similar configuration but with transistors of opposite type is the Sziklai pair, a Darlington pair behaves like a single transistor with a high current gain. In fact, integrated devices have three leads, broadly equivalent to those of a standard transistor, the maximum collector current IC of the pair is that of Q2. A typical integrated power device is the 2N6282, which includes a switch-off resistor and has a current gain of 2400 at IC=10A, a Darlington pair can be sensitive enough to respond to the current passed by skin contact even at safe voltages. Thus it can form the stage of a touch-sensitive switch. Darlington transistors can be used in circuits involving motors, relays, the current is amplified from the normal low level of the computer output line to the amount needed by the connected device. A typical modern device has a current gain of 1000 or more, however, this high current gain comes with several drawbacks. One drawback is a doubling of the base–emitter voltage.65 V when the device is operating in the active or saturated region. Another drawback of the Darlington pair is its increased saturation voltage, the output transistor is not allowed to saturate because the first transistor, when saturated, establishes full parallel negative feedback between the collector and the base of the second transistor. Thus the saturation voltage of a Darlington transistor is one VBE higher than a single transistor saturation voltage, for equal collector currents, this drawback translates to an increase in the dissipated power for the Darlington transistor over a single transistor. The increased low output level can cause troubles when TTL logic circuits are driven, another problem is a reduction in switching speed or response, because the first transistor cannot actively inhibit the base current of the second one, making the device slow to switch off. To alleviate this, the transistor often has a resistor of a few hundred ohms connected between its base and emitter terminals. This resistor provides a low-impedance discharge path for the charge accumulated on the base-emitter junction, the Darlington pair has more phase shift at high frequencies than a single transistor and hence can more easily become unstable with negative feedback. Insulated-gate bipolar transistor Sziklai pair ULN2003A U. S
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Sziklai pair
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In electronics, the Sziklai pair is a configuration of two bipolar transistors, similar to a Darlington pair. In contrast to the Darlington arrangement, the Sziklai pair has one NPN and one PNP transistor, the configuration is named for its early popularizer, George C. The current gain of the pair is similar to that of a Darlington pair and is the product of the current gains of the two transistors, the figure at the right illustrates an NPN-PNP pair that acts like a single NPN transistor overall. By replacing Q1 with a PNP transistor and Q2 with an NPN transistor the pair will act like a PNP transistor overall, in a typical application the Sziklai pair acts somewhat like a single transistor with the same type as Q1 and with a very high current gain. The emitter of Q2 acts the role of a collector, hence the emitter of Q2 is labeled C in the figure to the right. Likewise, in an application the collector of Q2 plays the role of an emitter and is thus labeled E. As with a Darlington pair, a resistor is connected between Q2s emitter and base to improve its turn-off time. One advantage over the Darlington pair is that the base voltage is only about 0. 6V or half of the Darlingtons 1. 2V nominal turn-on voltage. Like the Darlington, it can only to 0. 6V. Sziklai pairs are used in the output stages of power amplifiers due to their advantages both in linearity and bandwidth when compared with more common Darlington emitter follower output stages. They are especially advantageous in amplifiers where the load does not require the use of parallel devices. Sziklai pairs can also have the benefit of thermal stability under the right conditions. This means that power consumption is on the order of a few watts versus tens of watts for the same performance in many cases. This is a compelling reason to use the Sziklai pair in cases where output power is moderate, fidelity is critical. Historically, designers used the quasi-complementary configuration, which uses a Darlington push pair. Alternately, if a germanium PNP device were used, it would have different characteristics. Patent 2,966,632 Multistage semi-conductor signal translating circuits, patent 2,762,870 Push-pull complementary type transistor amplifier. Patent 2,791,644 Push-pull amplifier with complementary type transistors, G. C. Sziklai, May 7,1957 ECE327, Procedures for Output Filtering Lab — Section 4 discusses design of a BJT-Sziklai-pair-based class-AB current driver in detail
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Field-effect transistor
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The field-effect transistor is a transistor that uses an electric field to control the electrical behaviour of the device. FETs are also known as unipolar transistors since they involve single-carrier-type operation, many different implementations of field effect transistors exist. Field effect transistors generally display very high impedance at low frequencies. The conductivity between the drain and source terminals is controlled by a field in the device, which is generated by the voltage difference between the body and the gate of the device. The MOSFET, which superseded the JFET and had a profound effect on digital electronic development, was invented by Dawon Kahng. The device consists of a channel through which charge carriers, electrons or holes. Source and drain terminal conductors are connected to the semiconductor through ohmic contacts, the conductivity of the channel is a function of the potential applied across the gate and source terminals. The FETs three terminals are, Source, through which the carriers enter the channel, conventionally, current entering the channel at S is designated by IS. Drain, through which the carriers leave the channel, conventionally, current entering the channel at D is designated by ID. Gate, the terminal that modulates the channel conductivity, by applying voltage to G, one can control ID. All FETs have source, drain, and gate terminals that correspond roughly to the emitter, collector, most FETs have a fourth terminal called the body, base, bulk, or substrate. The size of the gate, length L in the diagram, is the distance between source and drain, the width is the extension of the transistor, in the direction perpendicular to the cross section in the diagram. Typically the width is larger than the length of the gate. A gate length of 1 µm limits the frequency to about 5 GHz,0.2 µm to about 30 GHz. The names of the terminals refer to their functions, the gate terminal may be thought of as controlling the opening and closing of a physical gate. This gate permits electrons to flow through or blocks their passage by creating or eliminating a channel between the source and drain, electron-flow from the source terminal towards the drain terminal is influenced by an applied voltage. The body simply refers to the bulk of the semiconductor in which the gate, source, usually the body terminal is connected to the highest or lowest voltage within the circuit, depending on the type of the FET. The FET controls the flow of electrons from the source to drain by affecting the size and shape of a channel created and influenced by voltage applied across the gate
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JFET
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The junction gate field-effect transistor is the simplest type of field-effect transistor. They are three-terminal semiconductor devices that can be used as electronically-controlled switches, amplifiers, unlike bipolar transistors, JFETs are exclusively voltage-controlled in that they do not need a biasing current. Electric charge flows through a channel between source and drain terminals. By applying a bias voltage to a gate terminal, the channel is pinched. A JFET is usually on when there is no difference between its gate and source terminals. Thus, JFETs are sometimes referred to as depletion-mode devices, JFETs can have an n-type or p-type channel. In the n-type, if the applied to the gate is less than that applied to the source. A JFET has an input impedance, which means that it has a negligible effect on external components or circuits connected to its gate. In 1947, researchers John Bardeen, Walter Houser Brattain, and they discovered the point-contact transistor in the course of trying to diagnose the reasons for their failures. The first practical JFETs were made a decade later, the JFET is a long channel of semiconductor material, doped to contain an abundance of positive charge carriers or holes, or of negative carriers or electrons. Ohmic contacts at each end form the source and the drain, a pn-junction is formed on one or both sides of the channel, or surrounding it, using a region with doping opposite to that of the channel, and biased using an ohmic gate contact. JFET operation can be compared to that of a garden hose, the current also depends on the electric field between source and drain. The depletion layer is so-called because it is depleted of mobile carriers, when the depletion layer spans the width of the conduction channel, pinch-off is achieved and drain-to-source conduction stops. Pinch-off occurs at a reverse bias of the gate-source junction. The pinch-off voltage varies considerably, even among devices of the same type, for example, VGS for the Temic J202 device varies from −0.8 V to −4 V. Typical values vary from −0.3 V to −10 V, to switch off an n-channel device requires a negative gate-source voltage. Conversely, to switch off a p-channel device requires positive VGS, in normal operation, the electric field developed by the gate blocks source-drain conduction to some extent. Some JFET devices are symmetrical with respect to the source and drain, the JFET gate is sometimes drawn in the middle of the channel
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MOSFET
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The metal–oxide–semiconductor field-effect transistor is a type of field-effect transistor. It has a gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals, although FET is sometimes used when referring to MOSFET devices, other types of field-effect transistors also exist. Because these two terminals are connected to each other internally, only three terminals appear in electrical diagrams. The basic principle of the transistor was first patented by Julius Edgar Lilienfeld in 1925. The main advantage of a MOSFET over a regular transistor is that it very little current to turn on. In enhancement mode MOSFETs, a voltage drop across the oxide induces a conducting channel between the source and drain contacts via the field effect. The term enhancement mode refers to the increase of conductivity with increase in oxide field that adds carriers to the channel, also referred to as the inversion layer. The channel can contain electrons, or holes, opposite in type to the substrate, so nMOS is made with a p-type substrate, the metal in the name MOSFET is now often a misnomer because the previously metal gate material is now often a layer of polysilicon. Aluminium had been the material until the mid-1970s, when polysilicon became dominant. Metallic gates are regaining popularity, since it is difficult to increase the speed of operation of transistors without metal gates, likewise, the oxide in the name can be a misnomer, as different dielectric materials are used with the aim of obtaining strong channels with smaller applied voltages. An insulated-gate field-effect transistor or IGFET is a term almost synonymous with MOSFET. The term may be inclusive, since many MOSFETs use a gate that is not metal. Another synonym is MISFET for metal–insulator–semiconductor FET, the MOSFET is by far the most common transistor in both digital and analog circuits, though the bipolar junction transistor was at one time much more common. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925. Twenty five years later, when Bell Telephone attempted to patent the junction transistor, they found Lilienfeld already holding a patent, Bell Labs was able to work out an agreement with Lilienfeld, who was still alive at that time. It was at time the Bell Labs version was given the name bipolar junction transistor, or simply junction transistor. In 1959, Dawon Kahng and Martin M. Atalla at Bell Labs invented the metal–oxide–semiconductor field-effect transistor as an offshoot to the patented FET design and it used crystalline silicon for the semiconductor and a thermally oxidized layer of silicon dioxide for the insulator
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MESFET
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MESFET stands for metal–semiconductor field-effect transistor. It is quite similar to a JFET in construction and terminology, the difference is that instead of using a p-n junction for a gate, a Schottky junction is used. Production MESFETs are operated up to approximately 45 GHz, and are used for microwave frequency communications. The first MESFETs were developed in 1966, and a year later their extremely high frequency RF microwave performance was demonstrated, the MESFET differs from the common insulated gate FET or MOSFET in that there is no insulator under the gate over the active switching region. The most critical aspect of the design is the gate metal extent over the switching region, generally the narrower the gate modulated carrier channel the better the frequency handling abilities, overall. Spacing of the source and drain with respect to the gate, MESFET current handling ability improves as the gate is elongated laterally, keeping the active region constant, however is limited by phase shift along the gate due to the transmission line effect. As a result, most production MESFETs use a built up top layer of low resistance metal on the gate, numerous MESFET fabrication possibilities have been explored for a wide variety of semiconductor systems. Some of the application areas are, Military communications As front end low noise amplifier of microwave receivers in both military radar devices and communication. Commercial optoelectronics Satellite communications As power amplifier for output stage of microwave links, field effect transistor High electron mobility transistor Heterojunction bipolar transistor
