Generally, an amplifier is any device that changes, usually increases, the amplitude of a signal. A machine is any device that uses Energy to perform some activity In the fields of communications, Signal processing, and in Electrical engineering more generally a signal is any time-varying or spatial-varying quantity The "signal" is usually voltage or current.
In popular use, the term today usually refers to an electronic amplifier, often as in audio applications. An electronic amplifier is a device for increasing the power and/or Amplitude of a signal. The relationship of the input to the output of an amplifier — usually expressed as a function of the input frequency — is called the transfer function of the amplifier, and the magnitude of the transfer function is termed the gain. A transfer function is a mathematical representation in terms of spatial or temporal frequency of the relation between the input and output of a ( linear time-invariant) In Electronics, gain is a measure of the ability of a circuit (often an Amplifier) to increase the power or Amplitude of a A related device that emphasizes conversion of signals of one type to another (for example, a light signal in photons to a DC signal in amperes) is a transducer, or a sensor. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Direct current ( DC) is the unidirectional flow of Electric charge. The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second A transducer is a device usually electrical, electronic, Electro-mechanical, Electromagnetic, Photonic, or Photovoltaic A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument However, a transducer does not amplify power. In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for
Contents
|
Figures of merit
The quality of an amplifier can be characterized by a number of specifications, enumerated below.
Gain
The gain of an amplifier is the ratio of output to input power or amplitude, and is usually measured in decibels. In Electronics, gain is a measure of the ability of a circuit (often an Amplifier) to increase the power or Amplitude of a A ratio is an expression which compares quantities relative to each other The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to (When measured in decibels it is logarithmically related to the power ratio: G(dB)=10 log(Pout/Pin)). In Mathematics, the logarithm of a number to a given base is the power or Exponent to which the base must be raised in order to produce
Bandwidth
The bandwidth (BW) of an amplifier is the range of frequencies for which the amplfier gives "satisfactory performance". Bandwidth is the difference between the upper and lower Cutoff frequencies of for example a filter, a Communication channel, or a Signal spectrum The "satisfactory performance" may be different for different applications. However, a common and well-accepted metric are the half power points (i. The half power point of an electronic amplifier stage is that frequency at which the output power has dropped to half of its mid-band level e. frequency where the power goes down by half its peak value) on the power vs. frequency curve. Therefore bandwidth can be defined as the difference between the lower and upper half power points. The half power point of an electronic amplifier stage is that frequency at which the output power has dropped to half of its mid-band level This is therefore also known as the −3 dB bandwidth. Bandwidths for other response tolerances are sometimes quoted (−1 dB, −6 dB etc. ).
A full-range audio amplifier will be essentially flat between 20 Hz to about 20 kHz (the range of normal human hearing. ) In minimalist amplifier design, the amp's usable frequency response needs to extend considerably beyond this (one or more octaves either side) and typically a good minimalist amplifier will have −3 dB points < 10 and > 65 kHz. Professional touring amplifiers often have input and/or output filtering to sharply limit frequency response beyond 20 Hz-20 kHz; too much of the amplifier's potential output power would otherwise be wasted on infrasonic and ultrasonic frequencies, and the danger of AM radio interference would increase. Infrasound is Sound with a Frequency too low to be heard by the human Ear. Modern switching amplifiers need steep low pass filtering at the output to get rid of high frequency switching noise and harmonics. A switching amplifier or class-D amplifier is an Electronic amplifier which in contrast to the active resistance used in linear mode AB-class amplifiers
Efficiency
Efficiency is a measure of how much of the input power is usefully applied to the amplifier's output. Class A amplifiers are very inefficient, in the range of 10–20% with a max efficiency of 25%. An electronic amplifier is a device for increasing the power and/or Amplitude of a signal. Class B amplifiers have a very high efficiency but are impractical because of high levels of distortion (See: Crossover distortion). Crossover distortion is a type of Distortion which is caused by switching between devices driving a load In practical design, the result of a tradeoff is the class AB design. Modern Class AB amps are commonly between 35–55% efficient with a theoretical maximum of 78. 5%. Commercially available Class D switching amplifiers have reported efficiencies as high as 97%. A switching amplifier or class-D amplifier is an Electronic amplifier which in contrast to the active resistance used in linear mode AB-class amplifiers Amplifiers of Class C-F are usually known to be very high efficiency amplifiers. The efficiency of the amplifier limits the amount of total power output that is usefully available. Note that more efficient amplifiers run much cooler, and often do not need any cooling fans even in multi-kilowatt designs. The reason for this is that the loss of efficiency produces heat as a byproduct of the energy lost during the conversion of power. In more efficient amplifiers there is less loss of energy so in turn less heat.
Linearity
An ideal amplifier would be a totally linear device, but real amplifiers are only linear within certain practical limits. When the signal drive to the amplifier is increased, the output also increases until a point is reached where some part of the amplifier becomes saturated and cannot produce any more output; this is called clipping, and results in distortion. A distortion is the alteration of the original shape (or other characteristic of an object image sound waveform or other form of information or representation
Some amplifiers are designed to handle this in a controlled way which causes a reduction in gain to take place instead of excessive distortion; the result is a compression effect, which (if the amplifier is an audio amplifier) will sound much less unpleasant to the ear. For these amplifiers, the 1 dB compression point is defined as the input power (or output power) where the gain is 1 dB less than the small signal gain.
Linearization is an emergent field, and there are many techniques, such as feedforward, predistortion, postdistortion, EER, LINC, CALLUM, cartesian feedback, etc. In Mathematics and its applications linearization refers to finding the Linear approximation to a function at a given point Feed-forward is a term describing a kind of System which reacts to changes in its environment usually to maintain some desired state of the system Predistortion is a technique used to improve the linearity of Radio transmitter Amplifiers Radio transmitter amplifiers in most telecommunications systems are , in order to avoid the undesired effects of the non-linearities.
Noise
This is a measure of how much noise is introduced in the amplification process. is a one volume manga created by Tsutomu Nihei as a prequel to his ten-volume work Blame!. Noise is an undesirable but inevitable product of the electronic devices and components. It is measured in either decibels or the peak output voltage produced by the amplifier when no signal is applied.
Output dynamic range
Output dynamic range is the range, usually given in dB, between the smallest and largest useful output levels. Dynamic range is a term used frequently in numerous fields to describe the Ratio between the smallest and largest possible values of a changeable quantity such as in Sound The lowest useful level is limited by output noise, while the largest is limited most often by distortion. is a one volume manga created by Tsutomu Nihei as a prequel to his ten-volume work Blame!. The ratio of these two is quoted as the amplifier dynamic range. More precisely, if S = maximal allowed signal power and N = noise power, the dynamic range DR is DR = (S + N ) /N. [1]
Slew rate
Slew rate is the maximum rate of change of output variable, usually quoted in volts per second (or microsecond). In Electronics, the slew rate represents the maximum rate of change of a signal at any point in a circuit Many amplifiers are ultimately slew rate limited (typically by the impedance of a drive current having to overcome capacitive effects at some point in the circuit), which may limit the full power bandwidth to frequencies well below the amplifier's small-signal frequency response. In Electronics, the slew rate represents the maximum rate of change of a signal at any point in a circuit
Rise time
The rise time, tr, of an amplifier is the time taken for the output to change from 10% to 90% of its final level when driven by a step input. In Electronics, when describing a Voltage or current Step function, rise time (also risetime) refers to the time required for a signal The step response of a system in a given initial state consists of the time evolution of its Outputs when its control inputs are Heaviside step functions For a Gaussian response system (or a simple RC roll off), the rise time is approximated by:
tr * BW = 0. Carl Friedrich Gauss (1777 &ndash 1855 is the Eponym of all of the topics listed below 35, where tr is rise time in seconds and BW is bandwidth in Hz. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second.
Settling time and ringing
Time taken for output to settle to within a certain percentage of the final value (say 0. 1%). This is usually specified for oscilloscope vertical amplifiers and high accuracy measurement systems. Ringing refers to an output that cycles above and below its final value, leading to a delay in reaching final value quantified by the settling time above. Electricity In electrical circuits ringing is an unwanted Oscillation of a Voltage or current.
Overshoot
In response to a step input, the overshoot is the amount the output exceeds its final, steady-state value. The step response of a system in a given initial state consists of the time evolution of its Outputs when its control inputs are Heaviside step functions The term overshoot has the following meanings Aviation In Aviation, an overshoot is an aborted landing
Stability factor
Stability is a major concern in RF and microwave amplifiers. Stability can refer to Aircraft flight Stability (aircraft In atmospheric fluid dynamics atmospheric stability, a measure of the turbulence Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 The degree of an amplifiers stability can be quantified by a so-called stability factor. There are several different stability factors, such as the Stern stability factor and the Linvil stability factor, which specify a condition that must be met for the absolute stability of an amplifier in terms of its two-port parameters. A Two-Port Network (or four-terminal network or quadripole) is an Electrical circuit or device with two pairs of terminals (i
Electronic amplifiers
There are many types of electronic amplifiers, commonly used in radio and television transmitters and receivers, high-fidelity ("hi-fi") stereo equipment, microcomputers and other electronic digital equipment, and guitar and other instrument amplifiers. An electronic amplifier is a device for increasing the power and/or Amplitude of a signal. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic For biologic transmitters see Transmitter substance. A transmitter is an electronic device which usually with the aid of an antenna This article is about a radio receiver for other uses see Radio (disambiguation. High fidelity or hi-fi reproduction is a term used by home stereo listeners and home audio enthusiasts ( Audiophiles to refer to high-quality reproduction The guitar is a Musical instrument with ancient roots that is used in a wide variety of musical styles An instrument amplifier is an Electronic amplifier that converts the inaudible electric or electronic signal from musical instruments such as an Electric guitar Critical components include active devices, such as vacuum tubes or transistors. Passivity is a property of engineering systems most commonly used in electronic engineering and control systems This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals A brief introduction to the many types of electronic amplifier follows.
Power amplifier
The term "power amplifier" is a relative term with respect to the amount of power delivered to the load and/or sourced by the supply circuit. In general a power amplifier is designated as the last amplifier in a transmission chain (the output stage) and is the amplifier stage that typically requires most attention to power efficiency. Efficiency considerations lead to various classes of power amplifier: see power amplifier classes. An electronic amplifier is a device for increasing the power and/or Amplitude of a signal.
Vacuum tube (valve) amplifiers
According to Symons, while semiconductor amplifiers have largely displaced valve amplifiers for low power applications, valve amplifiers are much more cost effective in high power applications such as "radar, countermeasures equipment, or communications equipment" (p. A valve amplifier or tube amplifier is a type of Electronic amplifier that make use of Vacuum tubes instead of solid-state Semiconductor 56). Many microwave amplifiers are specially designed valves, such as the klystron, gyrotron, traveling wave tube, and crossed-field amplifier, and these microwave valves provide much greater single-device power output at microwave frequencies than solid-state devices (p. A klystron is a specialized linear-beam Vacuum tube (evacuated electron tube Gyrotrons are high powered Vacuum tubes which emit Millimeter Wavelength beams by bunching Electrons with Cyclotron motion A traveling-wave tube (TWT is an electronic device used to amplify Radio frequency signals to high power usually in an electronic assembly known as a traveling-wave A crossed-field amplifier (CFA is a specialized Vacuum tube, first introduced in the mid-1950s and frequently used as a Microwave Amplifier in very-high-power 59). [2]
Transistor amplifiers
The essential role of this active element is to magnify an input signal to yield a significantly larger output signal. In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals A bipolar (junction transistor ( BJT) is a type of Transistor. An audio amplifier is an Electronic amplifier that amplifies low-power audio signals (signals composed primarily of frequencies between 20 Hertz to The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals The amount of magnification (the "forward gain") is determined by the external circuit design as well as the active device.
Many common active devices in transistor amplifiers are bipolar junction transistors (BJTs) and metal oxide semiconductor field-effect transistors (MOSFETs). A bipolar (junction transistor ( BJT) is a type of Transistor. The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals
Applications are numerous, some common examples are audio amplifiers in a home stereo or PA system, RF high power generation for semiconductor equipment, to RF and Microwave applications such as radio transmitters. A public address or " PA " system is an electronic amplification system with a mixer, Amplifier and Loudspeakers used to
Transistor-based amplifier can be realized using various configurations: for example with a bipolar junction transistor we can realize common base, common collector or common emitter amplifier; using a MOSFET we can realize common gate, common source or common drain amplifier. In Electronics, a common-base (also known as grounded-base) amplifier is one of three basic single-stage Bipolar junction transistor (BJT In Electronics, a common-collector (also known as an emitter follower or voltage follower) amplifier is one of three basic single-stage In Electronics, a common-emitter amplifier is one of three basic single-stage bipolar-junction-transistor (BJT amplifier topologies typically used In Electronics, a common-gate amplifier is one of three basic single-stage Field-effect transistor (FET amplifier topologies typically used as a In Electronics, a common-source amplifier is one of three basic single-stage Field-effect transistor (FET amplifier topologies typically used as In Electronics, a common-drain (also known as a source follower or voltage follower) amplifier is one of three basic single-stage Field Each configuration has different characteristic (gain, impedance. . . ).
Operational amplifiers (op-amps)
An operational amplifier is a solid state integrated circuit amplifier which employs external feedback for control of its transfer function or gain. An operational amplifier, often called an op-amp, is a DC - coupled high- Gain electronic voltage amplifier with differential An instrumentation (or instrumentational) amplifier is a type of Differential amplifier that has been outfitted with input buffers which eliminate In Electronics, gain is a measure of the ability of a circuit (often an Amplifier) to increase the power or Amplitude of a
Fully differential amplifiers (FDA)
A fully differential amplifier is a solid state integrated circuit amplifier which employs external feedback for control of its transfer function or gain. A fully differential amplifier, usually referred to as an ' FDA' for brevity is a DC - coupled high-gain electronic voltage amplifier with differential In Electronics, gain is a measure of the ability of a circuit (often an Amplifier) to increase the power or Amplitude of a It is similar to the operational amplifier but it also has differential output pins.
Video amplifiers
These deal with video signals and have varying bandwidths depending on whether the video signal is for SDTV, EDTV, HDTV 720p or 1080i/p etc. . The specification of the bandwidth itself depends on what kind of filter is used and which point (-1 dB or -3 dB for example) the bandwidth is measured. Certain requirements for step response and overshoot are necessary in order for acceptable TV images to be presented.
Oscilloscope vertical amplifiers
These are used to deal with video signals to drive an oscilloscope display tube and can have bandwidths of about 500 MHz. The specifications on step response, rise time, overshoot and aberrations can make the design of these amplifiers extremely difficult. One of the pioneers in high bandwidth vertical amplifiers was the Tektronix company. Tektronix Inc is a North American company best known for its test and measurement equipment such as Oscilloscopes Logic analyzers, and video and mobile
Distributed amplifiers
These use transmission lines to temporally split the signal and amplify each portion separately in order to achieve higher bandwidth than can be obtained from a single amplifying device. Distributed amplifiers are a very resourceful example of distributed Circuit design that incorporate Transmission line theory into traditional amplifier design A transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy Bandwidth is the difference between the upper and lower Cutoff frequencies of for example a filter, a Communication channel, or a Signal spectrum The outputs of each stage are combined in the output transmission line. This type of amplifier was commonly used on oscilloscopes as the final vertical amplifier. An oscilloscope (commonly abbreviated to scope or O-scope) is a type of Electronic test equipment that allows signal Voltages to be viewed The transmission lines were often housed inside the display tube glass envelope.
Microwave amplifiers
Travelling wave tube (TWT) amplifiers
Used for high power amplification at low microwave frequencies. A traveling-wave tube (TWT is an electronic device used to amplify Radio frequency signals to high power usually in an electronic assembly known as a traveling-wave They typically can amplify across a broad spectrum of frequencies; however, they are usually not as tunable as klystrons.
Klystrons
Very similar to TWT amplifiers, but more powerful and with a specific frequency "sweet spot". A klystron is a specialized linear-beam Vacuum tube (evacuated electron tube They generally are also much heavier than TWT amplifiers, and are therefore ill-suited for light-weight mobile applications. Klystrons are tunable, offering selective output within their specified frequency range.
Musical instrument (audio) amplifiers
An audio amplifier is usually used to amplify signals such as music or speech. An instrument amplifier is an Electronic amplifier that converts the inaudible electric or electronic signal from musical instruments such as an Electric guitar An audio amplifier is an Electronic amplifier that amplifies low-power audio signals (signals composed primarily of frequencies between 20 Hertz to
Other amplifier types
Carbon microphone
One of the first devices used to amplify signals was the carbon microphone (effectively a sound-controlled variable resistor). The carbon Microphone, also known as a carbon button microphone (or sometimes just a button microphone) or a carbon transmitter, is a sound-to-electrical A potentiometer is a three-terminal Resistor with a sliding contact that forms an adjustable Voltage divider. By channeling a large electric current through the compressed carbon granules in the microphone, a small sound signal could produce a much larger electric signal. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 The carbon microphone was extremely important in early telecommunications; analog telephones in fact work without the use of any other amplifier. Before the invention of electronic amplifiers, mechanically coupled carbon microphones were also used as amplifiers in telephone repeaters for long distance service. A repeater is an electronic device that receives a signal and Retransmits it at a higher level and/or higher power or onto the other side of an obstruction
Magnetic amplifier
A magnetic amplifier is a transformer-like device that makes use of the saturation of magnetic materials to produce amplification. The magnetic amplifier (colloquially known as the "mag amp" is an electromagnetic device for amplifying electrical signals A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors It is a non-electronic electrical amplifier with no moving parts. The bandwidth of magnetic amplifiers extends to the hundreds of kilohertz.
Rotating electrical machinery amplifier
A Ward Leonard control is a rotating machine like an electrical generator that provides amplification of electrical signals by the conversion of mechanical energy to electrical energy. Ward Leonard Control, also known as the Ward Leonard Drive System was a widely used DC motor speed control system introduced by Harry Ward Leonard in 1891 In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic Changes in generator field current result in larger changes in the output current of the generator, providing gain. This class of device was used for smooth control of large motors, primarily for elevators and naval guns.
Field modulation of a very high speed AC generator was also used for some early AM radio transmissions. [1] See Alexanderson alternator. An Alexanderson alternator is a rotating machine invented by Ernst Alexanderson for the generation of high frequency Alternating current up to 100 kHz
Johnsen-Rahbek effect amplifier
The earliest form of audio power amplifier was Edison's "electromotograph" loud-speaking telephone, which used a wetted rotating chalk cylinder in contact with a stationary contact. The friction between cylinder and contact varied with the current, providing gain. Edison discovered this effect in 1874, but the theory behind the Johnsen-Rahbek effect was not understood until the semiconductor era. The Johnsen-Rahbek effect occurs when an Electric potential is applied across the boundary between a Metallic surface and the surface of a semiconducting material
Mechanical amplifiers
Mechanical amplifiers were used in the pre-electronic era in specialized applications. Early autopilot units designed by Elmer Ambrose Sperry incorporated a mechanical amplifier using belts wrapped around rotating drums; a slight increase in the tension of the belt caused the drum to move the belt. An autopilot is a mechanical electrical or hydraulic system used to guide a vehicle without assistance from a human being Elmer Ambrose Sperry ( October 12, 1860 – June 16, 1930) was a prolific Inventor and Entrepreneur, most famous as co-inventor A paired, opposing set of such drives made up a single amplifier. This amplified small gyro errors into signals large enough to move aircraft control surfaces. A similar mechanism was used in the Vannevar Bush differential analyzer. Vannevar Bush ( March 11, 1890 &ndash June 30, 1974; pronounced "VAN-ee-var" ˈvæˌniː The differential analyser was a mechanical Analog computer designed to solve Differential equations by integration, using wheel-and-disc mechanisms to perform
Optical amplifiers
Optical amplifiers amplify light through the process of stimulated emission. An optical amplifier is a device that amplifies an Optical signal directly without the need to first convert it to an electrical signal Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 In Optics, stimulated emission is the process by which an electron perturbed by a Photon having the correct energy may drop to a lower Energy level resulting
Miscellaneous types
- There are also mechanical amplifiers, such as the automotive servo used in braking. A servomechanism, or servo is an automatic device which uses error-sensing Feedback to correct the performance of a mechanism A brake is a device for slowing or stopping the motion of a Machine or Vehicle, or alternatively a device to restrain it from starting to move again
- Relays can be included under the above definition of amplifiers, although their transfer function is not linear (that is, they are either open or closed). A relay is an electrical Switch that opens and closes under the control of another Electrical circuit. The word linear comes from the Latin word linearis, which means created by lines.
- Also purely mechanical manifestations of such digital amplifiers can be built (for theoretical, didactical purposes, or for entertainment), see e. g. domino computer. A domino computer is a mechanical Computer built using Dominoes to represent mechanical amplification of Digital signals Because of the existence
- Another type of amplifier is the fluidic amplifier, based on the fluidic triode. Fluidics (also known as Fluidic logic) is the use of a Fluid or compressible medium to perform analog or Digital operations similar to those Fluidics (also known as Fluidic logic) is the use of a Fluid or compressible medium to perform analog or Digital operations similar to those
References
- ^ Verhoeven CJM, van Staveren A, Monna GLE, Kouwenhoven MHL and Yildiz E (2003). Structured electronic design: negative feedback amplifiers. Boston/Dordrecht: Kluwer Academic, p. 10. ISBN 1-4020-7590-1.
- ^ Robert S. Symons (1998). "Tubes: Still vital after all these years". IEEE Spectrum 35 (4): 52–63.
See also
- Attenuator (electronics)
- Electronic amplifier
- Negative feedback amplifier
- Instrument amplifier
- Low noise amplifier
- Preamplifier
- Step response
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic