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The term amplifier as used in this article can mean either a circuit (or stage) using a single active device or a complete system such as a packaged audio hi-fi amplifier.
An electronic amplifier is a device for increasing the power of a signal. It does this by taking power from a power supply and controlling the output to match the input signal shape but with a larger amplitude. In this sense, an amplifier may be considered as modulating the output of the power supply. Real world amplifiers are not ideal and this control is thus imperfect. In physics, power (symbol: P) is the rate at which work is performed or energy is transferred. ...
In information theory, a signal is the sequence of states of a communications channel that encodes a message. ...
A wall wart style variable DC power supply with its cover removed. ...
- One consequence is that the power supply itself may influence the output, and must itself be considered when designing the amplifier
- The amplifier circuit has an "open loop" performance, that can be described by various parameters (gain, slew rate, output impedance, distortion, bandwidth, signal to noise ratio ...)
- Many modern amplifiers use negative feedback techniques to hold the gain at the desired value.
Classification of amplifier stages and systems
Different designs of amplifiers are used for different types of applications and signals. We can broadly divide amplifiers into four categories: - Small signal amplifiers
- Low frequency power amplifiers
- Radio frequency (RF) power amplifiers
- Microwave power amplifiers
Each of these calls for a slightly different design approach, mainly because of the physical limitations of the components used to implement the amplifier, and the efficiencies that can be realised. It has been suggested that this article or section be merged with Radio waves. ...
There are many alternative classifications that address different aspects of amplifier designs, and they all have some effect on the design parameters and objectives of the circuit. Amplifier design is always a compromise of numerous factors, such as cost, amount of power consumed, devices that have real-world imperfections, and the need to match the amplifier to the input signal as well as the output load.
Classification of amplifier stages by common terminal One set of these classifications include terms referring to “common terminal” connections, where the design is described by the terminal of the active device that is used as the signal ground. Examples include terms such as common emitter, common gate, or common drain, and these names also reflect the type of active device used to amplify the signal. For instance, common emitter refers to an amplifier with a bipolar transistor as the active device, while common plate would be for a vacuum tube amp, while a common drain amp would signify the use of MOSFET or JFET devices. Designs exist for almost any terminal of any active device to be held to ground in an amplifier, for different reasons that are reflected in each use. See also: common collector, common base. Common emitter amplifier, voltage divider bias (CEVDB) circuit configuration A common emitter is a type of electronic amplifier stage based on a bipolar transistor in series with a load element such as a resistor. ...
Common gate amplifier A common-gate amplifier is one of the common configurations of FET electronic amplifier. ...
A common-drain (commonly called a source follower) amplifier is one of the common configurations of FET electronic amplifier. ...
The metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is by far the most common field-effect transistor in both digital and analog circuits. ...
Electric current flow from source to drain in a p-channel JFET is restricted when a voltage is applied to the gate. ...
Typical common collector or emitter follower circuit. ...
Common base amplifier In electronics, common base refers to a type of bipolar transistor circuit configuration in which a transistor is connected such that its base terminal is wired to the ground or common rail of the circuit (or can be considered so for AC signals). ...
Inverting or non-inverting Another way to classify amps is the phase relationship of the input signal to the output signal. An inverting amplifier produces an output that is 180 degrees out of phase of the input signal, or a mirror image of it if viewed on an oscilloscope. A non-inverting amplifier maintains equal phase relationship between the input and output waveforms. An emitter follower is a type of this amplifier, indicating that the signal at the emitter of a transistor is following (matching phases with) the input signal. Illustration showing the interior of a cathode-ray tube for use in an oscilloscope. ...
This description can apply to a single stage or a complete system.
Function Other amplifiers may be classified by their function or output characteristics. These functional descriptions usually apply to complete amplifier systems or sub-systems and rarely to individual stages. - A servo amplifier indicates an integrated feedback loop to actively control the output at some desired level. A DC servo indicates use at frequencies down to DC levels, where the rapid fluctuations of an audio or RF signal do not occur. These are often used in mechanical actuators, or devices such as DC motors that must maintain a constant speed or torque. An AC servo amp can do this for some ac motors.
- A linear amplifier denotes that it has a precise amplification factor over a wide range of frequencies, and is often used to boost signals for relay in communications systems. A non-linear amp is made to amplify only a specific narrow or tuned frequency, to the exclusion of all other frequencies.
- An audio amplifier is designed for use in reproducing audio frequencies. This category subdivides into small signal amplification, and power amps which are optimised for driving speakers, sometimes with multiple amps grouped together as separate or bridgeable channels to accommodate different audio reproduction requirements.
- A special type of low power amplifier is widely used in instruments and for signal processing, among many other varied uses. These are known as operational amplifiers, (or op-amps). This is because this type of amplifier is used in circuits that perform mathematical algorithmic functions, or "operations" on input signals to obtain specific types of output signals. An idealised Op-amp has the following characteristics
- Differential inputs (one "inverting", one, "non-inverting" relative to the output)
- One output
- Infinite input impedance (so as to not load circuitry it is sampling as a control input)
- Zero output impedance
- Infinite gain
- Zero propagation delay
The performance of an op amp with these characteristics would be entirely defined by the (usually passive) components forming a negative feedback loop around it, ie the amplifier itself has no effect on the output. In cybernetics and control theory, feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. ...
Look up servo in Wiktionary, the free dictionary. ...
Electric motors of various sizes. ...
Torque applied via an adjustable end wrench Relationship between force, torque, and momentum vectors in a rotating system In physics, torque (or often called a moment) can informally be thought of as rotational force or angular force which causes a change in rotational motion. ...
It has been suggested that this article or section be merged with Radio waves. ...
Legend γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High...
In radio terminology, a receiver is an electronic circuit that receives a radio signal from an antenna and decodes the signal for use as sound, pictures, navigational-position information, etc. ...
Antenna tower of Crystal Palace transmitter, London A transmitter (sometimes abbreviated XMTR) is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ...
Sound reproduction is the electrical or mechanical re-creation and/or amplification of sound, often as music. ...
This article or section needs copy editing for grammar, style, cohesion, tone and/or spelling. ...
A 741 operational amplifier in a TO-5 metal can package An operational amplifier, usually referred to as an op-amp for brevity, is a DC-coupled high-gain electronic voltage amplifier with Differential Inputs and, usually, a single output. ...
Today, Op-amps are usually provided as integrated circuits rather than constructed from discrete components. All real world op-amps fall short of the idealised specification above - but some modern components have remarkable performance and come close in some respects
Voltage, current, and power amplification Amplifiers can be designed to increase signal voltage (voltage amp), current (buffer amp), or both (power amp), of an electronic signal. Electronic amplifiers can operate off either single sided supplies (either + or − voltage “rail”, or “bus”, and ground), or double-sided or balanced supplies (+ and − supply rails, and ground).
The different methods of supplying power result in many different methods of bias. Bias is the method by which the active devices are set up to operate properly, or by which the DC component of the output signal is set to the midpoint between the maximum voltages available from the power supply. Most amplifiers use sets of devices that are matched in specifications except for polarity. These are called complementary pairs. Class A amplifiers generally use only one device, unless the power supplies are set to provide both positive and negative supplies, in which case a dual device symmetrical design may be used. Class C amps, by definition, use a single polarity supply. In electrical engineering, the term bias has the following meanings: A systematic deviation of a value from a reference value. ...
Amplifiers are also often designed to have multiple stages hooked in series to increase gain. Each stage of these designs is often a different type of amp to suit the needs of each stage. For instance, the first stage might be a Class A stage, feeding a class AB push-pull second stage, which then drives a class G final output stage, taking advantage for the strengths of each type, while minimizing the weaknesses.
There also exist special “stacked” transistors, called Darlington pairs, which have two specially matched transistors in a single case. Transistors or other active devices are also often hooked in parallel, or “strapped”, in order to multiply the amount of current that the final output stage can deliver to the load. This is two transistors connected together so that the current amplified by the first is amplified further by the second transistor. ...
Interstage coupling method Audio amplifiers are sometimes classified by the coupling method of the signal at the input, output, or between stages. Different types of these include:
Each method has its advantages and compromises. Also see: Multistage amplifiers. Figure 1:Three-phase pole-mounted step-down transformer. ...
This article, image, template or category should belong in one or more categories. ...
Generally the voltage or current gain obtainable from a single stage transistor amplifier is insufficient for most applications. ...
In accordance with the frequency range - DC (direct coupled) – capable of amplifying even zero frequency (DC) signals
- Audio frequency (AF) – 20 Hz to 20 kHz
- Video amplifiers – up to few 100 MHz (<10 MHz for TV)
- Ultra High Frequency (UHF) – up to few GHz
This article, image, template or category should belong in one or more categories. ...
In accordance with the type of load - Untuned - (a) audio (b) video
- Tuned (RF amps) - used for amplifying a single radio frequency or band of frequencies
Angle of flow or conduction angle The letter system of amplifier classification assigns a letter to different designs of electronic amplifiers. These designs are classified according to the relationship between the input wave form and the output wave form, as well as the amount of time that the active components used to amplify a signal are conducting electricity. This time is measured in degrees of duration of sine wave test signal applied to the input of an amplifier, with 360 degrees representing one full cycle.
Implementation Amplifiers can be implemented using transistors of various types, or vacuum tubes (valves). Other more exotic forms of amplifier are also possible using different types of devices. Such exotic amplifiers are often used for microwave or other extremely high frequency signals. Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch. ...
Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ...
Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) frequencies, but relatively short for radio waves. ...
Extremely high frequency is the highest radio frequency band. ...
Amplifier classes Amplifier circuits are classified as A, B, AB and C for analog designs, and class D and E for switching designs. For the analog classes, each class defines what proportion of the input signal cycle (called the angle of flow) is used to actually switch on the amplifying device: It has been suggested that this article or section be merged with Analog electronics. ...
- Class A
- 100% of the input signal is used (conduction angle a = 360° or 2π)
- Class AB
- more than 50% but less than 100% is used. (181° to 359°, π < a < 2π)
- Class AB1 applies to tube or transistor amplifiers in class AB where the grid or base is more negatively biased than it is in class A.
- Class AB2 applies to tube or transistor amplifiers in class AB where the grid or base is often more negatively biased than in AB1, and the input signal is often larger. When the drive is high enough to make the grid or the base more positive, the grid or base current will increase. It is possible depending on the level of the signal input for the amplifier to move from class AB1 to AB2.
- Class B
- 50% of the input signal is used (a = 180° or π)
- Class C
- less than 50% is used (0° to 179°, a < π)
This can be most easily understood using the diagrams in each section below. For the sake of illustration, a bipolar junction transistor is shown as the amplifying device, but in practice this could be a MOSFET or vacuum tube device. In an analog amplifier, the signal is applied to the input terminal of the device (base, gate or grid), and this causes a proportional output drive current to flow out of the output terminal. The output drive current is obtained from the power supply. The voltage signal shown is thus a larger version of the input, but has been changed in sign (inverted) by the amplification. Other arrangements of amplifying device are possible, but that given (common emitter, common source or common cathode) is the easiest to understand and employ in practice. If the amplifying element is linear, then the output will be faithful copy of the input, only larger and inverted. In practice, transistors are not linear, and the output will only approximate the input. Non-linearity is the origin of distortion within an amplifier. Which class of amplifier (A, B, AB or C) depends on how the amplifying device is biased — in the diagrams the bias circuits are omitted for clarity. A bipolar junction transistor (BJT) is a type of transistor. ...
The metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is by far the most common field-effect transistor in both digital and analog circuits. ...
Electric current is the flow (movement) of electric charge. ...
Common emitter amplifier, voltage divider bias (CEVDB) circuit configuration A common emitter is a type of electronic amplifier stage based on a bipolar transistor in series with a load element such as a resistor. ...
Common source amplifier with input bias and capacitively coupled input and output. ...
Non-linearity is a slight distortion of a single frequency into multiple frequencies within the human or mammalian auditory system. ...
In electronics, voltage bias (sometimes simply called bias) is a steady-state voltage It is used to activate the active component like transistor transistor, coil or other source of load. ...
Any real amplifier is an imperfect realisation of an ideal amplifier. One important limitation of a real amplifier is that the output it can generate is ultimately limited by the power available from the power supply. An amplifier can saturate and clip the output if the input signal becomes too large for the amplifier to reproduce.
Class A Class A amplifiers amplify over the whole of the input cycle such that the output signal is an exact scaled-up replica of the input with no clipping. Class A amplifiers are the usual means of implementing small-signal amplifiers. They are not very efficient — a theoretical maximum of 50% is obtainable with inductive output coupling and only 25% with capacitive coupling. In a Class A circuit, the amplifying element is biased such that the device is always conducting to some extent, and is operated over the most linear portion of its characteristic curve (known as its transfer characteristic or transconductance curve). Because the device is always conducting, even if there is no input at all, power is wasted. This is the reason for its inefficiency. Transconductance, also known as mutual conductance, is a property of certain electronic components. ...
Class A Amplifier If high output powers are needed from a Class A circuit, the power wastage will become significant. For every watt delivered to the load, the amplifier itself will, at best, waste another watt. For large powers this will call for a large power supply and large heat sink to carry away the waste heat. Class A designs have largely been superseded for audio power amplifiers, though some audiophiles believe that Class A gives the best sound quality, due to it being operated in as linear a manner as possible. In addition, some aficionados prefer thermionic valve (or "tube") designs over transistors, for a number of reasons: Tubes are more commonly used in class A designs, which have an asymmetrical transfer function. This means that distortion of a sine wave creates both odd- and even-numbered harmonics. They claim that this sounds more "musical" than the purely odd harmonics produced by a symmetrical push-pull amplifier.[1][2] Though good amplifier design can avoid inducing any harmonic patterns in a sound reproduction system, the differences in harmonic content are essential to the sound of intentional electric guitar distortion. Another is that valves use many more electrons at once than a transistor, and so statistical effects lead to a "smoother" approximation of the true waveform — see shot noise for more on this. Field-effect transistors have similar characteristics to valves, so these are found more often in high quality amplifiers than bipolar transistors. Historically, valve amplifiers often used a Class A power amplifier simply because valves are large and expensive; Many Class A designs uses only a single device. Transistors are much cheaper, and so more elaborate designs that give greater efficiency but use more parts are still cost effective. A classic application for a pair of class A devices is the long-tailed pair, which is exceptionally linear, and forms the basis of many more complex circuits, including many audio amplifiers and almost all op-amps. Class A amplifiers are not often used for op-amps; they are sometimes used as medium-power, low-efficiency, and high-cost audio amplifiers. The power consumption is unrelated to the output power: at idle (no input), the power consumption is essentially the same as at high output volume. The result is low efficiency and high heat dissipation. diagram of Class A amplifer, created for article. ...
The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. ...
If an electric circuit has a well-defined output terminal, the circuit connected to this terminal (or its input impedance) is the load. ...
Sound is a disturbance of mechanical energy that propagates through matter as a wave. ...
An audiophile, from Latin audire[1] to hear and Greek philos[2] loving, can be generally defined as a person dedicated to achieving high fidelity in the recording and playback of music . ...
In electronics, a vacuum tube (American English) or (thermionic) valve (British English) is a device generally used to amplify a signal. ...
A transfer function is a mathematical representation of the relation between the input and output of a linear time-invariant system. ...
In trigonometry, an ideal sine wave is a waveform whose graph is identical to the generalized sine function y = Asin[ω(x − α)] + C, where A is the amplitude, ω is the angular frequency (2π/P where P is the wavelength), α is the phase shift, and C...
In acoustics and telecommunication, the harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. ...
Left: Rosa Hurricane, a heavy metal-style solid body guitar. ...
e- redirects here. ...
Photon noise simulation. ...
A long-tailed pair with current-mirror load and constant-current drive. ...
A 741 operational amplifier in a TO-5 metal can package An operational amplifier, usually referred to as an op-amp for brevity, is a DC-coupled high-gain electronic voltage amplifier with Differential Inputs and, usually, a single output. ...
An operational amplifier or op-amp is an electronic circuit module (normally built as an integrated circuit, but occasionally with discrete transistors or vacuum tubes) which has a non-inverting input (+), an inverting input (-) and one output. ...
Class B and AB Class B amplifiers only amplify half of the input wave cycle. As such they create a large amount of distortion, but their efficiency is greatly improved and is much better than Class A. Class B has a maximum theoretical efficiency of 78.5%. This is because the amplifying element is switched off altogether half of the time, and so cannot dissipate power. A single Class B element is rarely found in practice, though it can be used in RF power amplifiers where the distortion is unimportant. However Class C is more commonly used for this.
Class B Amplifier A practical circuit using Class B elements is the complementary pair or "push-pull" arrangement. Here, complementary devices are used to each amplify the opposite halves of the input signal, which is then recombined at the output. This arrangement gives excellent efficiency, but can suffer from the drawback that there is a small glitch at the "joins" between the two halves of the signal. This is called crossover distortion. A solution to this is to bias the devices just on, rather than off altogether when they are not in use. This is called Class AB operation. Each device is operated in a non-linear region which is only linear over half the waveform, but still conducts a small amount on the other half. Such a circuit behaves as a class A amplifier in the region where both devices are in the linear region, however the circuit cannot strictly be called class A if the signal passes outside this region, since beyond that point only one device will remain in its linear region and the transients typical of class B operation will occur. The result is that when the two halves are combined, the crossover is greatly minimised or eliminated altogether. Image File history File links No higher resolution available. ...
Crossover distortion is a type of distortion which is caused by switching between devices driving a load. ...
Class AB sacrifices some efficiency over class B for linearity, so will always be less efficient. (below 78.5%) It is typically much more efficient than class A.
Class B Push-Pull Amplifier Class B or AB push-pull circuits are the most common form of design found in audio power amplifiers. Class AB is widely considered a good compromise for audio amplifiers, since much of the time the music is quiet enough that the signal stays in the "class A" region, where it is reproduced with good fidelity, and by definition if passing out of this region, is large enough that the distortion products typical of class B are relatively small. Class B and AB amplifiers are sometimes used for RF linear amplifiers as well. Class B amplifiers are also favored in battery-operated devices, such as transistor radios. diagram of push-pull amplifer, created for article. ...
Regency TR-1. ...
Digital Class B A limited power output Class-B amplifier with a single-ended supply rail of 5V +/- 10%.
Class C Class C amplifiers conduct less than 50% of the input signal and the distortion at the output is high, but efficiencies of up to 90% can be reached. Some applications can tolerate the distortion, such as megaphones. A much more common application for Class C amplifiers is in RF transmitters, where the distortion can be vastly reduced by using tuned loads on the amplifier stage. The input signal is used to roughly switch the amplifying device on and off, which causes pulses of current to flow through a tuned circuit. The tuned circuit will only resonate at particular frequencies, and so the unwanted frequencies are dramatically suppressed, and the wanted full signal (sine wave) will be abstracted by the tuned load. Provided the transmitter is not required to operate over a very wide band of frequencies, this arrangement works extremely well. Other residual harmonics can be removed using a filter. A megaphone, with a three-inch lighter to scale. ...
Antenna tower of Crystal Palace transmitter, London A transmitter (sometimes abbreviated XMTR) is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ...
An LC circuit consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C. When connected together, an electrical current can alternate between them at an angular frequency of where L is the inductance in henries, and C is the capacitance in farads. ...
Class C Amplifier diagram of Class C amplifer, created for article. ...
Class D -
A class D amplifier is a power amplifier where all power devices are operated in on/off mode. Output stages such as those used in pulse generators are examples of class D amplifiers. Mostly though, the term applies to devices intended to reproduce signals with a bandwidth well below the switching frequency. These amplifiers use pulse width modulation, pulse density modulation (sometimes referred to as pulse frequency modulation) or more advanced form of modulation such as Delta-sigma modulation (see for example Analog Devices AD1990 Class-D audio power amplifier). The input signal is converted to a sequence of pulses whose averaged value is directly proportional to the amplitude of the signal at that time. The frequency of the pulses is typically ten or more times the highest frequency of interest in the input signal. The output of such an amplifier contains unwanted spectral components (i.e.. the pulse frequency and its harmonics) that must be removed by a passive filter. The resulting filtered signal is then an amplified replica of the input. Block diagram of a basic switching or PWM (Class-D) amplifier. ...
Pulse generators can either be internal circuits or pieces of electronic test equipment used to generate pulses (electronic impulses). ...
Pulse-width modulation of a signal or power source involves the modulation of its duty cycle to either convey information over a communications channel or control the amount of power sent to a load. ...
Pulse-density modulation, or PDM, is a form of modulation used to represent an analog signal in the digital domain. ...
The Delta-Sigma (ΔΣ) modulation is a kind of analog-to-digital or digital-to-analog conversion. ...
In acoustics and telecommunication, the harmonic of a wave is a component frequency of the signal that is an integral multiple of the fundamental frequency. ...
Television signal splitter consisting of a hi-pass and a low-pass filter. ...
The main advantage of a class D amplifier is power efficiency. Because the output pulses have a fixed amplitude, the switching elements (usually MOSFETs, but valves and bipolar transistors were once used) are switched either on or off, rather than operated in linear mode. This means that very little power is dissipated by the transistors except during the very short interval between the on and off states. The wasted power is low because the instantaneous power dissipated in the transistor is the product of voltage and current, and one or the other is almost always close to zero. The lower losses permit the use of a smaller heat sink while the power supply requirements are lessened too. The metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is by far the most common field-effect transistor in both digital and analog circuits. ...
The schematic symbols for pnp_ and npn_type BJTs. ...
CPU heat sink with fan attached A heat sink is an environment or object that absorbs and dissipates heat from another object using thermal contact (either direct or radiant). ...
A wall wart style variable DC power supply with its cover removed. ...
Class D amplifiers can be controlled by either analog or digital circuits. A digital controller introduces additional distortion called quantization error caused by its conversion of the input signal to a digital value. It has been suggested that this article or section be merged with Analog electronics. ...
Digital circuits are electric circuits based on a number of discrete voltage levels. ...
Class D amplifiers were widely used to control motors, and almost exclusively for small DC motors, but they are now also used as audio amplifiers, with some extra circuitry to allow analogue to be converted to a much higher frequency pulse width modulated signal. The relative difficulty of achieving good audio quality means that the vast majority appear in applications where quality is not a factor, such as miniature audio systems and "DVD-receivers". Rotating magnetic field as a sum of magnetic vectors from 3 phase coils An electric motor converts electrical energy into mechanical energy. ...
High quality Class D audio amplifiers are now, however, starting to appear in the market. Tripath have called their revised Class D designs Class T. Perhaps more famously, Bang and Olufsen's ICEPower Class D system has been used in the Alpine PDX range and some of the PRS range of Pioneer along with other manufacturers. These revised designs have been said to rival good traditional AB amplifiers in terms of quality.
Before these higher quality designs existed an earlier use of Class D amplifiers and prolific area of application is high-powered, subwoofer amplifiers in cars. Because subwoofers are generally limited to a bandwidth of no higher than 150 Hz, the switch speed for the amplifier does not have to be as high as for a full range amplifier. The drawback with Class D designs being used to power subwoofers is that their output filters (typically inductors that convert the pulse width signal back into an analogue waveform) lower the damping factor of the amplifier. This means that the amplifier cannot prevent the subwoofer's reactive nature from lessening the impact of low bass sounds (as explained in the feedback part of the Class AB section). Class D amplifiers for driving subwoofers have become so inexpensive that a true 1 kW of power output can be had for less than 250USD (retail). Efficiencies are in the 80% to 95% range. In audio system terminology the damping factor gives the ratio of the rated impedance of the loudspeaker to the source impedance. ...
D does not stand for "digital" The letter D used to designate this type of amplifier is simply the next letter after C, and does not stand for digital. Class D and Class E amplifiers are sometimes mistakenly described as "digital" because the output waveform superficially resembles a pulse-train of digital symbols, but a Class D amplifier merely converts an input waveform into a continuously pulse-width modulated (square wave) analog signal. (A digital waveform would be pulse-code modulated.) A digital system is one that uses discrete values (often electrical voltages), especially those representable as binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (ie, as in an analog system). ...
Pulse-width modulation of a signal or power source involves the modulation of its duty cycle to either convey information over a communications channel or control the amount of power sent to a load. ...
Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a digital (usually binary) code. ...
Specialty classes
Class E The class E/F amplifier is a highly efficient switching power amplifier, typically used at such high frequencies that the switching time becomes comparable to the duty time. As said in the class-D amplifier the transistor is connected via a serial-LC-circuit to the load, and connected via a large L (inductance) to the supply voltage. The supply voltage is connected to ground via a large capacitor to prevent any RF-signals leaking into the supply. The class-E amplifier adds a C between the transistor and ground and uses a defined L (RFC in the figure) to connect to the supply voltage.
Class E Amplifier The following description ignores DC, which can be added afterwards easily. The above mentioned C (Cp in the figure) and L are in effect a parallel LC-circuit to ground. When the transistor is on, it pushes through the serial LC-circuit into the load and some current begins to flow to the parallel LC-circuit to ground. Then the serial LC-circuit swings back and compensates the current into the parallel LC-circuit. At this point the current through the transistor is zero and it is switched off. Both LC-circuits are now filled with energy in the C and the Ls. The whole circuit performs a damped oscillation. The damping by the load has been adjusted so that some time later the energy from the Ls is gone into the load, but the energy in both Cs peaks at the original value, to in turn restore the original voltage, so that the voltage across the transistor is zero again and it can be switched on.
With load, frequency, and duty cycle (0.5) as given parameters and the constraint that the voltage is not only restored, but peaks at the original voltage, the four parameters (L,L,C,C) are determined. The class F-amplifier takes the finite on resistance into account and tries to make the current touch the bottom at zero. This means the voltage and the current at the transistor are symmetric with respect to time. The Fourier Transform allows an elegant formulation to generate the complicated LC-networks. It says that the first harmonic is passed into the load, all even harmonics are shorted and all higher odd harmonics are open. In mathematics, the Fourier transform is a certain linear operator that maps functions to other functions. ...
Class F and the even harmonics In push-pull amplifiers and in CMOS the even harmonics of both transistors just cancel. Experiment tells that a square wave can be generated by those amplifiers and math tells that square wave do consist of odd harmonics only. In a class D amplifier the output filter blocks all harmonics, that means the harmonics see an open load. So even small currents in the harmonics suffice to generate a voltage square wave. The current is in phase with the voltage applied to filter, but the voltage across the transistors is out of phase. Therefore there is a minimal overlap between current through the transistors and voltage across the transistors. The sharper the edges the lower the overlap. While class D sees the transistors and the load as two separate modules the class F admits imperfections like the parasitics of the transistor and tries to optimise the global system to have a high impedance at the harmonics. Of course there has to be a finite voltage across the transistor to push the current across the on state resistance. Because the combined current through both transistors is mostly in the first harmonic it looks like a sine. That means that in the middle of the square the maximum of current has to flow, so it may make sense to have a dip in the square or in other words to allow some over swing of the voltage square wave. A class F load network by definition has to transmit below a cut off frequency and to reflect above. Any frequency lying below the cut off and having its second harmonic above the cut off can be amplified, that is an octave bandwidth. On the other hand a LC series circuit with a large L and a tunable C may be simpler to implement. By reducing the duty cycle below 0.5, the output amplitude can be modulated. The voltage square waveform will degrade, but any overheating is compensated by the lower overall power flowing. Any load mismatch behind the filter can only act on the first harmonic current waveform, clearly only a purely resistive load makes sense, then the lower the resistance the higher the current. Class F can be driven by sine or by a square wave, for a sine the input can be tuned by an L to increase gain. If class F is implemented with a single transistor the filter is complicated to short the even harmonics.
All previous designs use sharp edges to minimise the overlap. Class E uses a significant amount of second harmonic voltage. The second harmonic can be used to reduce the overlap with edges with finite sharpness. For this to work energy on the second harmonic has to flow from the load into the transistor, and no source for this is visible in the circuit diagram. In reality the impedance is mostly reactive and the only reason for it is that class E is a class F amplifier with a very simplified load network and thus has to deal with imperfections. Note how in many amateur simulations of class E amplifiers sharp current edges are assumed nullifying the very motivation for class E and measurements near the transit frequency of the transistors show very symmetric curves, which look much similar to class F simulations.
Stuff belonging to class D:
The main concept used in this amplifier is to model the active switching device, such as a transistor or MOSFET, as a linear combination of two parts: (1) a (theoretical) "perfect" switching element, and (2) a complex network of parasitic elements attached to it (capacitors, inductors and resistors). After the decomposition, it becomes trivial to eliminate the losses of each part:
(1) The "perfect" switching element should be switched ON during zero-voltage crossing, and should be switched OFF during zero-current crossing. Thus the switching element either conducts current, or has some non-zero voltage on it, but never both at the same time. Because the dissipated power is equal to current x voltage, it becomes zero. This can be arranged by adjusting the phase (capacitor) and DC bias (resistor) of the signal going into the transistor input.
(2) The imaginary part of the impedance of the parasitic elements can be tuned, one by one, by matching them to another passive element with the complex conjugate impedance, thus leaving only the real part of the complex impedance. In mathematics, the imaginary part of a complex number z is the second element of the ordered pair of real numbers representing z, i. ...
Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ...
In mathematics, the complex conjugate of a complex number is given by changing the sign of the imaginary part. ...
In mathematics, a complex number is a number of the form where a and b are real numbers, and i is the imaginary unit, with the property i 2 = −1. ...
In theory, the only remaining loss is the real part of the impedance of the parasitic elements in the system, which cannot be avoided. This class of amplifier is unique to radio frequency ranges, where the amplifier analysis is usually done in the frequency domain and not in the voltage/current domain. This class is further divided to subclasses depending on which harmonics of the signal are taken into account during zero-voltage switching (ZVS) and zero-current switching (ZCS), with names such as Class E/F2,odd; Class F^-1; and so on. It is still an active area of research and new variants appear from time to time, usually with the letters "E" and "F" somewhere in class name. In mathematics, the real part of a complex number , is the first element of the ordered pair of real numbers representing , i. ...
The figure above shows a schematic of a class-E/F amplifier that uses this principle to achieve high efficiency.
The switch is periodically opened and closed at the frequency of operation. Usually, but not always, the switching duty ratio is 50%. The RF choke has comparatively large inductance so that in effect it functions as a constant current source. Other passive device values are chosen such that the following conditions are satisfied simultaneously. (1) The voltage across the switch at the instant of closing is zero. (2) The time derivative of voltage across the switch is at zero when the switch turns on. Moreover, Ls and Cs forms a resonating filter at the frequency of operation. In telecommunication and electronics, the term duty cycle has the following meanings: The duty cycle D is defined as the ratio between the pulse duration () and the period (T) of a rectangular waveform In a periodic phenomenon, the ratio of the duration of the phenomenon in a given period to...
A Choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. ...
In practical implementations a transistor is substituted for a switch, but is operated either in saturation (on) or in cut-off (off). The theoretical efficiency of a class-E amplifier is 100% with ideal components. However, practical circuits do exhibit a number of weaknesses that make them less than 100% efficient. These effects include finite switching speed, finite on-resistance and non-zero saturation voltage of the transistor as well as lossy passive components at high frequencies. Typical efficiency is about 60% at an operating frequency of 1–2 GHz.
This amplifier class is specially designed for the amplification of square waves, such as those used to transmit data in purely digital form. “Square” waves or pulses have special needs due to their frequency characteristics, since they require the faithful reproduction of the very high frequencies present in their leading and trailing edges, without adding artifacts such as ringing or overshoot during the amplification process. Consideration must be made as well for the lower frequency components introduced by the switching levels, such as the impedance of the output load, which is often in the form of a transmission line.
The class E amplifier was invented in 1972 by Nathan O. Sokal and Alan D. Sokal, and details were first published in 1975.[3] Some earlier reports on this operating class have been published in Russian. Alan David Sokal (born 1955) is a physicist at New York University. ...
Class G This section may require cleanup to meet Wikipedia's quality standards.
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Demonstration of Theoretical efficiency of Class G amplifier part1
 Demonstration of Theoretical efficiency of Class G amplifier part2 Class G amplifiers are a more efficient version of class AB amplifiers, which use "rail switching" to decrease power consumption and increase efficiency. The amplifier has several power rails at different voltages, and switches between rails as the signal output approaches each. Thus the amp increases efficiency by reducing the wasted power at the output transistors. Image File history File links Circle-question-red. ...
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Class H A Class H amplifier takes the idea of Class G one step further creating an infinite number of supply rails. This is done by modulating the supply rails 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. Significant efficiency gains can be achieved but with the drawback of more complicated supply design and reduced THD performance.
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Efficiency Class H
Doherty amplifiers A hybrid configuration receiving new attention is the Doherty amplifier, invented in 1934 by William H. Doherty for Bell Laboratories (whose sister company, Western Electric, was then an important manufacturer of radio transmitters). The Doherty amplifier consists of a class-B main (or "carrier") stage in parallel with a class-C auxiliary (or "peaking") stage. The input signal is split evenly to drive the two amplifiers, and a combining network sums the two output signals and corrects for phase differences between the two amplifiers. During periods of low signal level, the class-B amplifier efficiently operates on the signal and the class-C amplifier is inactive and consumes no power. During high signal peaks the class-B amplifier saturates and the class-C amplifier kicks in. The efficiency of previous AM transmitter designs was proportional to modulation, but with average modulation typically 20 percent, transmitters were limited to less than 50 percent efficiency. In Doherty's design, even with zero modulation a transmitter could achieve at least 60 percent efficiency.[4] Bell Telephone Laboratories or Bell Labs was originally the research and development arm of the United States Bell System, and was the premier corporate facility of its type, developing a range of revolutionary technologies from telephone switches to specialized coverings for telephone cables, to the transistor. ...
Company Masthead Logo Logo until circa 1969, also current logo on company web site Logo 1969-1983 Western Electric (sometimes abbreviated WE and WECo) was an American electrical engineering company, the manufacturing arm of AT&T from 1881 to 1995. ...
The Doherty amplifier remains in use in very-high-power AM transmitters, but for lower-power AM transmitters, vacuum-tube amplifiers in general were eclipsed in the 1980s by arrays of solid-state amplifiers, which could be switched on and off with much finer granularity in response to the requirements of the input audio. However, interest in the Doherty configuration has been revived by cellular-telephone and wireless-Internet applications where the sum of several constant-envelope users creates an aggregate AM result. The main challenge of the Doherty amplifier for digital transmission modes is in aligning the two stages and getting the class-C amplifier to turn on and off very quickly.
Other classes Several audio amplifier manufacturers have started "inventing" new classes as a way to differentiate themselves. These class names usually do not reflect any revolutionary amplification technique, and are used mostly for marketing purposes. This can easily be determined by the fact that the class name is trademarked or copyrighted. For example, Crowns K and I-Tech Series as well as several other models utilise Crowns patented Class-I (or BCA) technology. Lab Gruppen use a form of class D amplifier called class TD or Tracked Class D which tracks the waveform to more accurately amplify it without the drawbacks of traditional class D amplifiers.
"Class T" is a trademark of TriPath company, which manufactures audio amplifier IC's. This new class "T" is a revision of the common class D amplifier, but with changes to ensure fidelity over the full audio spectrum, unlike traditional class D designs. It operates at a frequency of 650 kHz, with a proprietary modulator. A Class T amplifier is a type of audio amplifier developed by Tripath Technology. ...
Class Z is a trademark of Zetex semiconductor is a direct digital feedback technology.
A practical circuit For the purposes of illustration, this practical amplifier circuit is described. It could be the basis for a moderate-power audio amplifier. It features a typical (though substantially simplified) design as found in modern amplifiers, with a class AB push-pull output stage, and uses some overall negative feedback. Bipolar transistors are shown, but this design would also be realisable with FETs or valves.
A practical amplifier circuit The input signal is coupled through capacitor C1 to the base of transistor Q1. The capacitor allows the AC signal to pass, but blocks the DC bias voltage established by resistors R1 and R2 so that any preceding circuit is not affected by it. Q1 and Q2 form a differential amplifier (an amplifier that multiplies the difference between two inputs by some constant), in an arrangement known as a long-tailed pair. This arrangement is used to conveniently allow the use of negative feedback, which is fed from the output to Q2 via R7 and R8. The negative feedback into the difference amplifier allows the amplifier to compare the input to the actual output. The amplified signal from Q1 is directly fed to the second stage, Q3, which provides further amplification of the signal, and the DC bias for the output stages, Q4 and Q5. R6 provides the load for Q3 (A better design would probably use some form of active load here, such as a constant-current sink). So far, all of the amplifier is operating in Class A. The output pair are arranged in Class AB push-pull, also called a complementary pair. They provide the majority of the current amplification and directly drive the load, connected via DC-blocking capacitor C2. The diodes D1 and D2 provide a small amount of constant voltage bias for the output pair, just biasing them into the conducting state so that crossover distortion is minimised. This design is simple, but a good basis for a practical design because it automatically stabilises its operating point, since feedback internally operates from DC up through the audio range and beyond. Further circuit elements would probably be found in a real design that would roll off the frequency response above the needed range to prevent the possibility of unwanted oscillation. Also, the use of fixed diode bias as shown here can cause problems if the diodes are not both electrically and thermally matched to the output transistors — if the output transistors turn on too much, they can easily overheat and destroy themselves, as the full current from the power supply is not limited at this stage. A common solution to help stabilise the output devices is to include some emitter resistors, typically an ohm or so. Calculating the values of the circuit's resistors and capacitors is done based on the components employed and the intended use of the amp. circuit of amplifier created to go with article File links The following pages link to this file: Electronic amplifier Categories: GFDL images ...
Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ...
City lights viewed in a motion blurred exposure. ...
Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...
Resistor symbols (non-European) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ...
Simple form of a differential amplifier A differential amplifier is a type of an electronic amplifier that multiplies the difference between two inputs by some constant factor (the differential gain). ...
A long-tailed pair with current-mirror load and constant-current drive. ...
Types of diodes. ...
Frequency response is the measure of any systems response to frequency, but is usually used in connection with electronic amplifiers and similar systems, particularly in relation to audio signals. ...
Oscillation is the variation, typically in time, of some measure as seen, for example, in a swinging pendulum. ...
For the basics of radio frequency amplifiers using valves, see Valved RF amplifiers. For the purposes of illustration, these practical amplifier circuits are described. ...
See also Image File history File links Nuvola_apps_ksim. ...
Mission Cyrus 1 Hi Fi integrated audio amplifier An audio amplifier is an electronic amplifier that works with audio frequencies (generally 20 hertz to 20,000 hertz). ...
A valve (UK) audio amplifier or vacuum tube (US) audio amplifier is a valve amplifier used for sound recording, reinforcement, or reproduction. ...
The low noise amplifier (LNA) is a special type of electronic amplifier or amplifier used in communication systems to amplify very weak signals captured by an antenna. ...
A 741 operational amplifier in a TO-5 metal can package An operational amplifier, usually referred to as an op-amp for brevity, is a DC-coupled high-gain electronic voltage amplifier with Differential Inputs and, usually, a single output. ...
An instrument amplifier is an electronic amplifier designed for use with an electric or electronic musical instrument, such as an electric guitar. ...
This article or section does not adequately cite its references or sources. ...
Typical instrumentation amplifier schematic An instrumentation amplifier is a type of differential amplifier that has been specifically designed to have characteristics suitable for use in measurement and test equipment. ...
The charge-transfer amplifier (CTA) is an electronic amplifier circuit. ...
Distributed amplifiers are a very resourceful example of distributed circuit design that incorporate transmission line theory into traditional amplifier design in order to arrive at an amplifier with a larger gain-bandwidth product than is realizable by conventional circuits. ...
It has been suggested that this article or section be merged into Electronic amplifier. ...
References This article or section does not cite any references or sources. ...
is the 218th day of the year (219th in leap years) in the Gregorian calendar. ...
Bell Telephone Laboratories or Bell Labs was originally the research and development arm of the United States Bell System, and was the premier corporate facility of its type, developing a range of revolutionary technologies from telephone switches to specialized coverings for telephone cables, to the transistor. ...
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