Chopper amplifier wikipedia
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Chopper amplifier wikipedia
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Category:Optical choppers
Provisions that are valid at a general level e. The structural association with elements coupled with amplifiers can be classified either in H03F or in the subclass covering the element or in both the subclasses , depending on which aspect is more relevant.
In particular H03F units represented as "black boxes" in a specific application e. Amplifiers capable only of dealing with pulses, electronic switches, comparators, logic circuits, PWM signals.
As general remark, it must be noted that multiple classification symbols may be given. The philosophy is to classify documents in several sub-groups as the case may be, i. The following IPC groups, which are mostly related to discharge tube amplifiers or general type amplifiers, are used to classify circuit topologies based also on vacuum tubes, valve amplifiers, due to historical reasons see vacuum tube amplifier in the "Glossary of terms" section below :.
Amplifying devices operating in class A conduct in their linear range over the whole of the input cycle. Amplifying devices operating in class B conduct in their linear range half of the time and are turned off for the other half. Amplifying devices operating in class AB conduct in their linear range for more than half of the time. Amplifying devices operating in class C conduct in their linear range for less than half of the time.
In the basic class-D amplifier the input signal is converted into a sequence of pulse width modulated PWM pulses via a comparator C. Said PWM sequence is amplified via switching amplifying devices and filtered in order to produce an amplified replica of said input signal at the output.
The basic topology of class-E amplifier includes a transistor T, operated as a switch, a shunt capacitor C1 which includes the intrinsic transistor output capacitance, RF choke inductor L1 , a load resistor R, a series resonance circuit Co, Lo , and an excess inductance XL. The reactive elements shape the current and voltage waveforms across the transistor as shown.
Thus as current flows, there is essentially no voltage across the device and a highly efficient switching power amplifier is achieved. In realizing a class F amplifier, the active device operates primarily as a switch and the output network, generally, is designed to yield short circuit impedances at even harmonics of the fundamental frequency and to yield open circuit impedances at odd harmonics of the fundamental frequency.
The Class G amplifiers which use "rail switching" to decrease power consumption and increase efficiency provide several power rails at different voltages HV, LV and switch between them as the signal output approaches each level. Thus, the amplifier increases efficiency by reducing the wasted power at the output transistors. Class-H amplifiers take the idea of class G one step further creating an infinitely variable supply rail.
This is done by modulating the supply rails VCC, VEE so that the rails are only a few volts larger than the output signal at any given time.
The output stage operates at its maximum efficiency all the time. Switched-mode power supplies can be used to create the tracking rails. Class S amplifiers are used essentially for RF transmitters or as tracking power supply building blocks.
The basic architecture consists of a modulator, e. Amplifier with two or more amplifying elements having their DC paths in series with the load, the control electrode of each element being excited by at least part of the input signal drawing extracted from US Amplifier using a main and one or several auxiliary peaking amplifiers wherein the load is connected to the main amplifier using an impedance inverter.
The amplifying devices are each used for amplifying the opposite halves of the input signal. Push pull amplifier wherein the output terminals of the amplifying elements are tied together as a single ended output without additional balun elements. The common-mode rejection ratio is defined as:.
Until the invention of the transistor in , all practical amplifiers were made using Vacuum tubes, which rely on thermionic emission of electrons from a hot filament cathode , that then travel through a vacuum toward a collecting electrode anode.
The simplest vacuum tube was invented by John Ambrose Fleming while working for the Marconi Company in London in and named the diode, as it had two electrodes. The diode conducted electricity in one direction only and was used as a radio detector and a rectifier. In Lee De Forest added a third electrode grid and invented the first electronic amplifying device, the triode, which he named the Audion. This additional control grid modulates the current that flows between cathode and anode.
Two or more amplifying devices wherein the output terminal of the first device is connected to the input control terminal of the second device in order to form a chain of amplifying elements. The output voltage "follows" the input voltage, because the voltage gain almost equals one. Bipolar transistors are in Darlington configuration when they have the collector terminals tied together and the emitter of the first transistor is connected to the base of the second transistor so that the current gain of the composite transistor is increased.
Two amplifying devices are in bridge type when the output signal of one device is in opposition of phase with the output signal of the other device. A load is connected between the two amplifying device outputs, bridging the output terminals. This can double the voltage swing at the load as compared with the same amplifying device used alone without bridging. Esaki diode is a type of semiconductor diode which is capable of very fast operation, well into the microwave frequency region, by using quantum mechanical effects.
When forward-biased, an odd effect occurs called "quantum mechanical tunnelling" which gives rise to a region where an increase in forward voltage is accompanied by a decrease in forward current negative resistance region.
A basic chopper amplifier is formed by adding so-called choppers S1 and S2 before and after an input stage A1. The choppers consist of switches with two positions. In the first position, the inputs I1 and I2 are connected to the outputs O1 and O2, respectively.
In the second position, the inputs I1 and I2 are connected to the outputs O2 and O1, respectively. The choppers S1 and S2 are synchronized to repeatedly switch between the first and the second positions at the rate of a clock signal f1.
This configuration is commonly used to reduce the offset e. Vos1 and the flicker noise. The basis configuration of a long-tailed pair LTP differential amplifier consists of two amplifying transistors, which are connected so that the BJT emitters or FET sources, or valve cathodes are connected together.
The common electrodes are then connected to a circuit, forming the "long tail" of the name, the long tail providing a current source, i. The basic configuration of a PI type differential amplifier consists of two amplifying transistors, which are connected so that the BJT emitters or FET sources, or valve cathodes are connected together via a resistor.
The resistor terminals are then respectively connected to a shunting current source, forming the "PI" of the name, so that high common mode rejection ratio is achieved. The basic configuration of a pseudo differential amplifier consists of two amplifying transistors, wherein the BJT emitters or FET sources, or valve cathodes are not connected together but directly coupled to the ground. Thus, since the difference between I1 and I2 is output in proportion to the difference between gate signals Va, Vb, the configuration acts as a differential transconductance amplifier drawing extracted from US In a basic reflex amplifier an AC input signal is amplified and then rectified and, using the same circuit elements, the fed back resultant rectified DC signal is again amplified.
The reflex circuit thus achieves two stages of amplification, plus rectification, in a single stage. A travelling wave tube TWT integrated with a regulated power supply and protection circuits is referred to as a travelling wave-tube amplifier TWTA. The basic configuration of a TWT is an elongated vacuum tube with an electron gun a heated cathode that emits electrons at one end.
A magnetic containment field around the tube focuses the electrons into a beam, which then passes down the middle of an RF circuit wire helix or coupled cavity that stretches from the RF input to the RF output, the electron beam finally striking a collector at the other end. A directional coupler, which can be either a waveguide or an electromagnetic coil, fed with the low-powered radio signal that is to be amplified, is positioned near the emitter, and induces a current into the helix.
The RF circuit acts as a delay line, in which the RF signal travels at near the same speed along the tube as the electron beam. The electromagnetic field due to the RF signal in the RF circuit interacts with the electron beam, causing bunching of the electrons an effect called velocity modulation , and the electromagnetic field due to the beam current then induces more current back into the RF circuit i.
A second directional coupler, positioned near the collector, receives an amplified version of the input signal from the far end of the RF circuit. A klystron amplifies RF signals by converting the kinetic energy in a DC electron beam into radio frequency power.
A beam of electrons is produced by a thermionic cathode a heated pellet of low work function material , and accelerated by high-voltage electrodes typically in the tens of kilovolts.
This beam is then passed through an input cavity. RF energy is fed into the input cavity at, or near, its natural frequency to produce a voltage which acts on the electron beam. The electric field causes the electrons to bunch: electrons that pass through during an opposing electric field are accelerated and later electrons are slowed, causing the previously continuous electron beam to form bunches at the input frequency.
To reinforce the bunching, a klystron may contain additional "buncher" cavities. The RF current carried by the beam will produce an RF magnetic field, and this will in turn excite a voltage across the gap of subsequent resonant cavities. In the output cavity, the developed RF energy is coupled out. The spent electron beam, with reduced energy, is captured in a collector. The Envelope elimination and restoration technique was first proposed in by L.
Kahn as a way to linearise nonlinear amplifiers. In Kahn's approach, an RF input signal is processed by two parallel paths. In one path, the envelope of the RF input signal is "eliminated" using a limiting amplifier that removes any amplitude modulation and which provides a phase modulated signal. In the other path, the RF input signal envelope is detected, amplified, and applied to the PA as an amplitude modulating power supply voltage.
The EER technique allows the phase modulated signal to be amplified with high efficiency using a saturated power amplifier, which has an amplitude modulating power supply voltage, in order to restore the RF signal envelope at the output of said amplifier and to obtain linear amplification of the RF input signal.
In the Envelope Tracking configuration, the power amplifier is fed with a fully-modulated RF signal RFin at the input and supplied with a modulated drain bias Vout in accordance with the envelope of the modulated signal Venv. As a result, the power amplifier at all times is kept near saturation where the efficiency is highest.
A charge amplifier is a current integrator driven by an electrical source with capacitive nature such as a piezoelectric sensor. Contrary to what its name may suggest, a charge amplifier does not amplify the electric charge present at its input it can amplify only the exciting input voltage. The charge amplifier just transfers the input charge to another reference capacitor and produces an output voltage equal to the voltage across the reference capacitor. Thus the output voltage is proportional to the charge of the reference capacitor and, respectively, to the input charge; hence the circuit acts as a charge-to-voltage converter.
Charge amplifiers are usually constructed using op-amps with a feedback capacitor. Note: all the drawings of the present section, when not explicitly indicated, have been extracted from Wikipedia. Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements, wherein said details are addressing a specific technical effect for the amplification:. Modifications of amplifiers to raise the efficiency, wherein said modification comprises the following techniques:.
Transmitter circuits with power amplifiers having gain or transmission power control, with means for improving efficiency. Gain control details, gain control by varying the supply voltage, gain control dependent on the supply voltage. Modification of amplifiers to achieve frequency stabilisation or signal isolation among amplifying stages, wherein said modification comprises the following techniques:.
Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:. Modifications of amplifiers to reduce influence of variations of supply voltage in case of switching on or off of a power supply, i.
Modifications of amplifiers to reduce influence of variations of temperature or supply voltage, or other physical parameters, wherein said modifications comprise:. Modifications of amplifiers to reduce non-linear distortion, wherein said modifications comprise:. Analog transmitter circuits with power amplifiers with linearisation using predistortion and using feed-forward. Negative-feedback-circuit arrangements with or without positive feedback, wherein said arrangements comprises:.
Optical chopper
Zero-drift amplifiers dynamically correct their offset voltage and reshape their noise density. Two commonly used types—auto-zero amplifiers and choppers—achieve nanovolt-level offsets and extremely low offset drifts due to time and temperature. In addition, zero-drift amplifiers have higher open-loop gain, power-supply rejection, and common-mode rejection as compared to standard amplifiers; and their overall output error is less than that obtained by a standard precision amplifier in the same configuration. Examples can be found in precision weigh scales, medical instrumentation, precision metrology equipment, and infrared-, bridge-, and thermopile sensor interfaces. The offset voltage of the nulling amplifier is measured and stored on capacitor CM1. The offset voltage of the main amplifier is measured and stored on capacitor CM2, while the stored voltage on capacitor CM1 adjusts for the offset of the nulling amplifier. The overall offset is then applied to the main amplifier while processing the input signal.
Types of Chopper Circuits
Note: this box searches only for keywords in the titles of encyclopedia articles. For full-text searches on the whole website, use our search page. Note: the article keyword search field and some other of the site's functionality would require Javascript, which however is turned off in your browser. Find more supplier details at the end of this encyclopedia article , or go to our. Using our ad package , you can display your logo and further below your product description. There are different kinds of optical chopper devices which can be used for periodically transmitting and interrupting a light beam — for example, a laser beam — with mechanical means. Usually, they are used for periodically modulating the optical power of a beam. See below for some examples of applications. The simple mechanical operation principle — letting a beam pass or block it with some blade — makes such devices work for basically any optical wavelength, and beam distortions in the open state are avoided. This is in contrast to the use of various kinds of intensity modulators , which may exhibit incomplete transmission, beam distortions, effects of nonlinearities etc.
Ask The Applications Engineer—39: Zero-Drift Operational Amplifiers
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Known as: Chopper , Chopper electronic , Chopper control. In electronics, a chopper circuit is used to refer to numerous types of electronic switching devices and circuits used in power control and signal… Expand.
Physics:Input offset voltage
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Operational amplifier
The Reader View of Wikipedia. Power electronics is the application of solid-state electronics to the control and conversion of electric power. The first high power electronic devices were made using mercury-arc valves. In contrast to electronic systems concerned with transmission and processing of signals and data, in power electronics substantial amounts of electrical energy are processed. The power range is typically from tens of watts to several hundred watts. In industry, a common application is the variable speed drive VSD that is used to control an induction motor.
Chopper (electronics)
An ideal op-amp amplifies the differential input; if this input difference is 0 volts i. However, due to manufacturing process, the differential input transistors of real op-amps may not be exactly matched. This causes the output to be zero at a non-zero value of differential input, called the input offset voltage. This can be reduced to several microvolts if nulled using the IC's offset null pins or using higher-quality or laser-trimmed devices.
Precision Monolithics
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Chopper (electronics)
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A chopper circuit is used to refer to numerous types of electronic switching devices and circuits. The term has become somewhat ill-defined, and as a result is much less used nowadays than it was perhaps 30 or more years ago. A chopper is a static device that converts fixed dc input to a variable dc output voltage directly. A chopper may be thought of as an ac transformer since they behave in an identical manner.
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