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Active Device
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 (but does not produce) energy (thermodynamic passivity), or a component that is incapable of power gain (incremental passivity). A component that is not passive is called an ACTIVE COMPONENT. An electronic circuit consisting entirely of passive components is called a passive circuit (and has the same properties as a passive component). 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, while control systems engineers will use this to refer to THERMODYNAMICALLY PASSIVE ones. Systems for which the small signal model is not passive are sometimes called locally active (e.g. transistors and tunnel diodes). Systems that can generate power about a time-variant unperturbed state are often called parametrically active (e.g. certain types of nonlinear capacitors)
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Analog Electronics
ANALOGUE ELECTRONICS (also spelled ANALOG ELECTRONICS) are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two levels . The term "analogue" describes the proportional relationship between a signal and a voltage or current that represents the signal. The word analogue is derived from the Greek word ανάλογος (analogos) meaning "proportional". CONTENTS * 1 Analogue signals * 2 Inherent noise * 3 Analogue vs digital electronics * 3.1 Noise
Noise
* 3.2 Precision * 3.3 Design difficulty * 4 See also * 5 References ANALOGUE SIGNALS Main article: Analogue signal An analogue signal uses some attribute of the medium to convey the signal's information. For example, an aneroid barometer uses the angular position of a needle as the signal to convey the information of changes in atmospheric pressure . Electrical signals may represent information by changing their voltage, current, frequency, or total charge. Information is converted from some other physical form (such as sound, light, temperature, pressure, position) to an electrical signal by a transducer which converts one type of energy into another (e.g. a microphone ). The signals take any value from a given range, and each unique signal value represents different information
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Control System
A CONTROL SYSTEM manages, commands, directs or regulates the behaviour of other devices or systems. It can range from a home heating controller using a thermostat controlling a domestic boiler to large Industrial control systems which are used for controlling processes or machines. In the most common form, the _feedback control system _ it is desired to control a process, called the _plant _, so its output follows a _control signal _, which may be a fixed or changing value. The control system compares the output of the plant to the control signal, and applies the difference as an error signal to bring the output of the plant closer to the control signal
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Gain (electronics)
In electronics , GAIN is a measure of the ability of a two-port circuit (often an amplifier ) to increase the power or amplitude of a signal from the input to the output port by adding energy converted from some power supply to the signal. It is usually defined as the mean ratio of the signal amplitude or power at the output port to the amplitude or power at the input port. It is often expressed using the logarithmic decibel (dB) units ("dB gain"). A gain greater than one (greater than zero dB), that is amplification , is the defining property of an active component or circuit, while a passive circuit will have a gain of less than one. The term gain alone is ambiguous, and can refer to the ratio of output to input voltage (voltage gain), current (current gain) or electric power (power gain). In the field of audio and general purpose amplifiers , especially operational amplifiers , the term usually refers to voltage gain, but in radio frequency amplifiers it usually refers to power gain. Furthermore, the term gain is also applied in systems such as sensors where the input and output have different units; in such cases the gain units must be specified, as in "5 microvolts per photon" for the responsivity of a photosensor
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Electronic Circuit
An ELECTRONIC CIRCUIT is composed of individual electronic components , such as resistors , transistors , capacitors , inductors and diodes , connected by conductive wires or traces through which electric current can flow. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, and data can be moved from one place to another. Circuits can be constructed of discrete components connected by individual pieces of wire, but today it is much more common to create interconnections by photolithographic techniques on a laminated substrate (a printed circuit board or PCB) and solder the components to these interconnections to create a finished circuit. In an integrated circuit or IC, the components and interconnections are formed on the same substrate, typically a semiconductor such as silicon or (less commonly) gallium arsenide . An electronic circuit can usually be categorized as an analog circuit , a digital circuit , or a mixed-signal circuit (a combination of analog circuits and digital circuits). Breadboards , perfboards , and stripboards are common for testing new designs. They allow the designer to make quick changes to the circuit during development
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Small-signal Modeling
SMALL-SIGNAL MODELING is a common analysis technique in electronics engineering which is used to approximate the behavior of electronic circuits containing nonlinear devices with linear equations . It is applicable to electronic circuits in which the AC signals , the time-varying currents and voltages in the circuit, have a small magnitude compared to the DC bias currents and voltages. A small-signal model is an AC equivalent circuit in which the nonlinear circuit elements are replaced by linear elements whose values are given by the first-order (linear) approximation of their characteristic curve near the bias point. CONTENTS * 1 Overview * 2 Variable notation * 3 Example: PN junction diodes * 4 Differences between small signal and large signal * 5 See also * 6 References OVERVIEWMany of the electrical components used in simple electric circuits, such as resistors , inductors , and capacitors are linear , which means the current in them is proportional to the applied voltage . Circuits made with these components, called linear circuits , are governed by linear differential equations , and can be solved easily with powerful mathematical methods such as the Laplace transform
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Voltage Source
A VOLTAGE SOURCE is a two terminal device which can maintain a fixed voltage . An ideal voltage source can maintain the fixed voltage independent of the load resistance or the output current. However, a real-world voltage source cannot supply unlimited current. A voltage source is the dual of a current source . Real-world sources of electrical energy, such as batteries, generators, and power systems, can be modeled for analysis purposes as a combination of an ideal voltage source and additional combinations of impedance elements. A schematic diagram of a real voltage source, V, driving a resistor, R, and creating a current I CONTENTS * 1 Ideal voltage sources * 2 Comparison between voltage and current sources * 3 References and notes * 4 See also IDEAL VOLTAGE SOURCESAn IDEAL VOLTAGE SOURCE is a two-terminal device that maintains a fixed voltage drop across its terminals. It is often used as a mathematical abstraction that simplifies the analysis of real electric circuits. If the voltage across an ideal voltage source can be specified independently of any other variable in a circuit, it is called an INDEPENDENT voltage source. Conversely, if the voltage across an ideal voltage source is determined by some other voltage or current in a circuit, it is called a DEPENDENT or CONTROLLED VOLTAGE SOURCE
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Current Source
A CURRENT SOURCE is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it. A current source is the dual of a voltage source . The term, constant-current _sink_, is sometimes used for sources fed from a negative voltage supply. Figure 1 shows the schematic symbol for an ideal current source, driving a resistor load . There are two types. An INDEPENDENT CURRENT SOURCE (or sink) delivers a constant current. A DEPENDENT CURRENT SOURCE delivers a current which is proportional to some other voltage or current in the circuit
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Resistor
A RESISTOR is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines , among other uses. High-power resistors that can dissipate many watts of electrical power as heat may be used as part of motor controls, in power distribution systems, or as test loads for generators . Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity. Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment . Practical resistors as discrete components can be composed of various compounds and forms. Resistors are also implemented within integrated circuits . The electrical function of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude . The nominal value of the resistance falls within the manufacturing tolerance , indicated on the component
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Capacitor
A CAPACITOR is a passive two-terminal electrical component that stores electrical energy in an electric field . The effect of a capacitor is known as capacitance . While capacitance exists between any two electrical conductors of a circuit in sufficiently close proximity, a capacitor is specifically designed to provide and enhance this effect for a variety of practical applications by consideration of size, shape, and positioning of closely spaced conductors, and the intervening dielectric material. A capacitor was therefore historically first known as an electric CONDENSER. The physical form and construction of practical capacitors vary widely and many capacitor types are in common use. Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte . The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass , ceramic , plastic film , paper , mica , and oxide layers . Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor , an ideal capacitor does not dissipate energy
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Inductor
An INDUCTOR, also called a COIL or REACTOR, is a passive two-terminal electrical component that stores electrical energy in a magnetic field when electric current is flowing through it. An inductor typically consists of an electric conductor, such as a wire, that is wound into a coil around a core. When the current flowing through an inductor changes, the time-varying magnetic field induces a voltage in the conductor, described by Faraday\'s law of induction . According to Lenz's law, the direction of induced electromotive force (_e.m.f._) opposes the change in current that created it. As a result, inductors oppose any changes in current through them. An inductor is characterized by its inductance , which is the ratio of the voltage to the rate of change of current. In the International System of Units (SI), the unit of inductance is the henry (H). Inductors have values that typically range from 1 µH (10−6H) to 1 H. Many inductors have a magnetic core made of iron or ferrite inside the coil, which serves to increase the magnetic field and thus the inductance. Along with capacitors and resistors , inductors are one of the three passive linear circuit elements that make up electronic circuits. Inductors are widely used in alternating current (AC) electronic equipment, particularly in radio equipment. They are used to block AC while allowing DC to pass; inductors designed for this purpose are called chokes
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Transistor
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 transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits . The transistor is the fundamental building block of modern electronic devices , and is ubiquitous in modern electronic systems. Julius Edgar Lilienfeld patented a field-effect transistor in 1926 but it was not possible to actually 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 , and William Shockley . 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, and Shockley shared the 1956 Nobel Prize in Physics for their achievement
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Tunnel Diode
A TUNNEL DIODE or ESAKI DIODE is a type of semiconductor that is capable of very fast operation, well into the microwave frequency region, made possible by the use of the quantum mechanical effect called tunneling . It was invented in August 1957 by Leo Esaki
Leo Esaki
, Yuriko Kurose and Takashi Suzuki when they were working at Tokyo Tsushin Kogyo, now known as Sony
Sony
. In 1973 Esaki received the Nobel Prize in Physics , jointly with Brian Josephson , for discovering the electron tunneling effect used in these diodes . 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 (100 Å ) 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
Sony
in 1957 followed by General Electric
General Electric
and other companies from about 1960, and are still made in low volume today. Tunnel diodes are usually made from germanium , but can also be made from gallium arsenide and silicon materials. They are used in frequency converters and detectors
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Metamaterial
A METAMATERIAL (from the Greek word μετά _meta_, meaning "beyond") is a material engineered to have a property that is not found in nature. They are made from assemblies of multiple elements fashioned from composite materials such as metals or plastics. The materials are usually arranged in repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. Metamaterials derive their properties not from the properties of the base materials, but from their newly designed structures. Their precise shape , geometry , size , orientation and arrangement gives them their smart properties capable of manipulating electromagnetic waves : by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials. Appropriately designed metamaterials can affect waves of electromagnetic radiation or sound in a manner not observed in bulk materials. Those that exhibit a negative index of refraction for particular wavelengths have attracted significant research. These materials are known as negative-index metamaterials
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Port (circuit Theory)
In electrical circuit theory , a PORT is a pair of terminals connecting an electrical network or circuit to an external circuit, a point of entry or exit for electrical energy. A port consists of two nodes (terminals ) connected to an outside circuit, that meets the port condition; the currents flowing into the two nodes must be equal and opposite. The use of ports helps to reduce the complexity of circuit analysis. Many common electronic devices and circuit blocks, such as transistors , transformers , electronic filters , and amplifiers , are analyzed in terms of ports. In multiport network analysis , the circuit is regarded as a "black box " connected to the outside world through its ports. The ports are points where input signals are applied or output signals taken. Its behavior is completely specified by a matrix of parameters relating the voltage and current at its ports, so the internal makeup or design of the circuit need not be considered, or even known, in determining the circuit's response to applied signals. The concept of ports can be extended to waveguides, but the definition in terms of current is not appropriate and the possible existence of multiple waveguide modes must be accounted for
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Supremum
In mathematics , the INFIMUM (abbreviated INF; plural INFIMA) of a subset S of a partially ordered set T is the greatest element in T that is less than or equal to all elements of S, if such an element exists. Consequently, the term greatest lower bound (abbreviated as GLB) is also commonly used. The SUPREMUM (abbreviated SUP; plural SUPREMA) of a subset S of a partially ordered set T is the least element in T that is greater than or equal to all elements of S, if such an element exists. Consequently, the supremum is also referred to as the least upper bound (or LUB). The infimum is in a precise sense dual to the concept of a supremum. Infima and suprema of real numbers are common special cases that are important in analysis , and especially in Lebesgue integration . However, the general definitions remain valid in the more abstract setting of order theory where arbitrary partially ordered sets are considered. The concepts of infimum and supremum are similar to minimum and maximum , but are more useful in analysis because they better characterize special sets which may have no minimum or maximum. For instance, the positive real numbers ℝ+* does not have a minimum, because any given element of ℝ+* could simply be divided in half resulting in a smaller number that is still in ℝ+*
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