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Power amplifier classes
Power amplifier classes
Power amplifier classes
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In electronics, power amplifier classes are letter symbols applied to different power amplifier types. The class gives a broad indication of an amplifier's efficiency, linearity and other characteristics.

Broadly, as you go up the alphabet, the amplifiers become more efficient but less linear, and the reduced linearity is dealt with through other means.

The first classes, A, AB, B, and C, are related to the time period that the active amplifier device is passing current, expressed as a fraction of the period of a signal waveform applied to the input.[1] This metric is known as conduction angle (). A class-A amplifier is conducting through the entire period of the signal (°); class-B only for one-half the input period (°), class-C for much less than half the input period (°).

Class-D and E amplifiers operate their output device in a switching manner; the fraction of the time that the device is conducting may be adjusted so a pulse-width modulation output (or other frequency based modulation) can be obtained from the stage.

Additional letter classes are defined for special-purpose amplifiers, with additional active elements, power supply improvements, or output tuning; sometimes a new letter symbol is also used by a manufacturer to promote its proprietary design.

By December 2010, classes AB and D dominated nearly all of the audio amplifier market with the former being favored in portable music players, home audio and cell phone owing to lower cost of class-AB chips.[2]

In the illustrations below, a bipolar junction transistor is shown as the amplifying device. However, the same attributes are found with MOSFETs or vacuum tubes.

Class A

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Class-A amplifier

In a class-A amplifier, 100% of the input signal is used (conduction angle °). The active element remains continuously conducting.[3] Their output stage transistors are biased for class-A operation, leading to a continual drain current. This means class-A amplifiers have poor efficiency and heat is generated in the transistor, typically requiring thermal management.

Subclasses A1 and A2 are sometimes used to refer to vacuum-tube class-A amplifiers that drive the grid slightly negative or positive respectively on signal peaks for slightly more power than normal class-A.[4][5] This, however, incurs higher signal distortion[citation needed].

Advantages of class-A amplifiers

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  • Simplicity. Class-A amplifiers are typically single-ended, requiring just a single device. The usual push–pull output configuration for class-AB and -B amplifiers requires two connected devices in the circuit, one to handle each half of the waveform.
  • The amplifying element is biased so the device is always conducting, the quiescent (small-signal) collector current (for BJTs; drain current for FETs or anode/plate current for vacuum tubes) is close to the most linear portion of its transconductance curve.
  • Because the device operates continuously there is no "turn on" time, no problems with charge storage, and generally better high-frequency performance and feedback loop stability (and usually fewer high-order harmonics).
  • The point where the device comes closest to being 'off' is not at 'zero signal', so the problems of crossover distortion associated with class-AB and -B designs is avoided.
  • Good for amplifying the weak signals received by radio receivers due to low distortion.

Disadvantage of class-A amplifiers

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  • Class-A amplifiers are inefficient. A maximum theoretical efficiency of 25% is obtainable using usual configurations, but 50% is the maximum for a transformer or inductively coupled configuration.[6][7] In a power amplifier, this not only wastes power and limits operation with batteries, but increases operating costs and requires higher-rated output devices. Inefficiency comes from the standing current, which must be roughly half the maximum output current, and a large part of the power supply voltage is present across the output device at low signal levels. If high output power is needed from a class-A circuit, the power supply and accompanying heat becomes significant. For every watt delivered to the load, the amplifier itself, at best, uses an extra watt. For high-power amplifiers this means very large and expensive power supplies and heat sinks.
  • Because the output devices are in full operation at all times (unlike a class A/B amplifier), they will not have as long a life unless the amplifier is specifically designed to take this into account, adding to the cost of maintaining or designing the amplifier.

Class-A power amplifier designs have largely been superseded by more efficient designs, though their simplicity makes them popular with some hobbyists. There is a market for expensive high fidelity class-A amps considered a "cult item" among audiophiles[8] mainly for their absence of crossover distortion and reduced odd-harmonic and high-order harmonic distortion. Class-A power amplifiers are also used in some "boutique" guitar amplifiers due to their unique tonal quality and for reproducing vintage tones.

Single-ended and triode class-A amplifiers

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Some hobbyists who prefer class-A amplifiers also prefer the use of thermionic valve (tube) designs instead of transistors, for several reasons:

  • Single-ended output stages have an asymmetrical transfer characteristics curve, meaning that even-order harmonics in the created distortion tend to not cancel out (as they do in push–pull output stages). For tubes, or FETs, most distortion is second-order harmonics, from the square law transfer characteristic, which to some produces a "warmer" and more pleasant sound.[9][10]
  • For those who prefer low distortion figures, the use of tubes with class A (generating little odd-harmonic distortion, as mentioned above) together with symmetrical circuits (such as push–pull output stages, or balanced low-level stages) results in the cancellation of most of the even distortion harmonics, hence the removal of most of the distortion.
  • Historically, valve amplifiers were often used as a class-A power amplifier simply because valves are large and expensive; many class-A designs use only a single device.

Transistors are much less expensive than tubes so more elaborate designs that use more parts are still less expensive to manufacture than tube designs. 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 may be used in output stages of op-amps[11] (although the accuracy of the bias in low cost op-amps such as the "741" may result in class-A or class-AB or class-B performance, varying from device to device or with temperature). They are sometimes used as medium-power, low-efficiency, and high-cost audio power 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.

Class B

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Ideal class-B (push–pull) amplifier. In practice, distortion occurs near the crossover point.

In a class-B amplifier, the active device conducts for 180 degrees of the cycle (conduction angle θ = 180°). Because only half the waveform is amplified, significant harmonic distortion is directly present in the output signal. Therefore, class-B amplifiers are generally operated with tuned loading - where harmonics are shorted to ground by a series of resonators. Another method of reducing distortion, especially at audio frequencies, is to use two transistor devices in a push-pull configuration. Each conducts for one half (180°) of the signal cycle, and the device currents are combined so that the load current is continuous.[12]

At radio frequency, if the coupling to the load is via a tuned circuit, a single device operating in class B can be used because the stored energy in the tuned circuit supplies the "missing" half of the waveform. Devices operating in class-B are used in linear amplifiers, so called because the radio frequency output power is proportional to the square of the input excitation voltage. This is more easily understood if stated as "output voltage is proportional to input voltage, thus output power is proportional to input power." This characteristic prevents distortion of amplitude-modulated or frequency-modulated signals passing through the amplifier. Such amplifiers have an efficiency around 60%.[13]

When Class-B amplifiers amplify the signal with two active devices, each operates over one half of the cycle. Efficiency is much improved over class-A amplifiers.[14] Class-B amplifiers are also favoured in battery-operated devices, such as transistor radios. Class-B has a maximum theoretical efficiency of π/4 (≈ 78.5\%).[15]

A practical circuit using class-B elements is the push–pull stage, such as the very simplified complementary pair arrangement shown at right. Complementary devices are each used for amplifying the opposite halves of the input signal, which is then recombined at the output. This arrangement gives good efficiency, but usually suffers from the drawback that there is a small mismatch in the cross-over region – at the "joins" between the two halves of the signal, as one output device has to take over supplying power exactly as the other finishes. This is called crossover distortion. An improvement is to bias the devices so they are not completely off when they are not in use. This approach is called class AB operation.

Class AB

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Ideal class-AB amplifier

In a class-AB amplifier, the conduction angle is intermediate between class-A and -B (conduction angle θ > 180°); each one of the two active elements conducts more than half of the time. Class-AB is widely considered a good compromise for amplifiers, since many types of input signal are nominally quiet enough to stay in the "class-A" region, where they are amplified with good fidelity, and by definition if passing out of this region, will be large enough that the distortion products typical of class-B will be relatively small. The crossover distortion can be reduced further by using negative feedback.

In class-AB operation, each device operates the same way as in class-B over half the waveform, but also conducts a small amount on the other half.[16] As a result, the region where both devices simultaneously are nearly off (the "dead zone") is reduced. The result is that when the waveforms from the two devices are combined, the crossover is greatly minimised or eliminated altogether. The exact choice of quiescent current (the standing current through both devices when there is no signal) makes a large difference to the level of distortion (and to the risk of thermal runaway, which may damage the devices). Often, bias voltage applied to set this quiescent current must be adjusted with the temperature of the output transistors. (For example, in the circuit shown at right, the diodes would be mounted physically close to the output transistors, and specified to have a matched temperature coefficient.) Another approach (often used with thermally tracking bias voltages) is to include small value resistors in series with the emitters.

Class-AB sacrifices some efficiency over class-B in favor of linearity, thus is less efficient (below 78.5% for full-amplitude sine waves in transistor amplifiers, typically; much less is common in class-AB vacuum-tube amplifiers). It is typically much more efficient than class-A.

Suffix numbers for vacuum tube amplifiers

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A vacuum tube amplifier design will sometimes have an additional suffix number for the class, for example, class-B1. A suffix 1 indicates that grid current does not flow during any part of the input waveform, where a suffix 2 indicates grid current flows for part of the input waveform. This distinction affects the design of the driver stages for the amplifier. Suffix numbers are not used for semiconductor amplifiers.[17]

Class C

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Class-C amplifier

In a class-C amplifier, less than 50% of the input signal is used (conduction angle θ < 180°). Distortion is high and practical use requires a tuned circuit as load. Efficiency can reach 80% in radio-frequency applications.[13]

The usual application for class-C amplifiers is in RF transmitters operating at a single fixed carrier frequency, where the distortion is controlled by a tuned load on the amplifier. The input signal is used to switch the active device, causing pulses of current to flow through a tuned circuit forming part of the load.[18]

The class-C amplifier has two modes of operation: tuned and untuned.[19] The diagram shows a waveform from a simple class-C circuit without the tuned load. This is called untuned operation, and the analysis of the waveforms shows the massive distortion that appears in the signal. When the proper load (e.g., an inductive-capacitive filter plus a load resistor) is used, two things happen. The first is that the output's bias level is clamped with the average output voltage equal to the supply voltage. This is why tuned operation is sometimes called a clamper. This restores the waveform to its proper shape, despite the amplifier having only a one-polarity supply. This is directly related to the second phenomenon: the waveform on the center frequency becomes less distorted. The residual distortion is dependent upon the bandwidth of the tuned load, with the center frequency seeing very little distortion, but greater attenuation the farther from the tuned frequency that the signal gets.

The tuned circuit resonates at one frequency, the fixed carrier frequency, and so the unwanted frequencies are suppressed, and the wanted full signal (sine wave) is extracted by the tuned load. The signal bandwidth of the amplifier is limited by the Q-factor of the tuned circuit but this is not a serious limitation. Any residual harmonics can be removed using a further filter.

In practical class-C amplifiers a tuned load is invariably used. In one common arrangement the resistor shown in the circuit above is replaced with a parallel-tuned circuit consisting of an inductor and capacitor in parallel, whose components are chosen to resonate at the frequency of the input signal. Power can be coupled to a load by transformer action with a secondary coil wound on the inductor. The average voltage at the collector is then equal to the supply voltage, and the signal voltage appearing across the tuned circuit varies from near zero to near twice the supply voltage during the RF cycle. The input circuit is biased so that the active element (e.g., transistor) conducts for only a fraction of the RF cycle, usually one-third (120 degrees) or less.[20]

The active element conducts only while the collector voltage is passing through its minimum. By this means, power dissipation in the active device is minimised, and efficiency increased. Ideally, the active element would pass only an instantaneous current pulse while the voltage across it is zero: it then dissipates no power and 100% efficiency is achieved. However practical devices have a limit to the peak current they can pass, and the pulse must therefore be widened, to around 120 degrees, to obtain a reasonable amount of power, and the efficiency is then 60–70%.[20]

Class D

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Main article: Class-D amplifier
Block diagram of a basic switching or PWM (class-D) amplifier.
Boss Audio class-D mono amplifier with a low-pass filter for powering subwoofers

Class-D amplifiers use some form of pulse-width modulation to control the output devices. The conduction angle of each device is no longer related directly to the input signal but instead varies in pulse width.

In the class-D amplifier the active devices (transistors) function as electronic switches instead of linear gain devices; they are either on or off. The analog signal is converted to a stream of pulses that represents the signal by pulse-width modulation, pulse-density modulation, delta-sigma modulation or a related modulation technique before being applied to the amplifier. The time average power value of the pulses is directly proportional to the analog signal, so after amplification the signal can be converted back to an analog signal by a passive low-pass filter. The purpose of the output filter is to smooth the pulse stream to an analog signal, removing the high-frequency spectral components of the pulses. The frequency of the output pulses is typically ten or more times the highest frequency in the input signal to amplify, so that the filter can adequately reduce the unwanted harmonics and accurately reproduce the input.[21]

The main advantage of a class-D amplifier is power efficiency. Efficiency over 90% is achievable with MOSFETs and >80% is fairly common. Because the output pulses have a fixed amplitude, the switching elements (usually MOSFETs, but vacuum tubes and bipolar transistors have also been used) are switched completely on or completely off, rather than operating in linear mode. A MOSFET generally operates with the lowest on-state resistance when fully on and thus (excluding when fully off) has the lowest power dissipation when in that condition. Compared to an equivalent class-AB device, a class-D amplifier's lower losses permit the use of smaller heat sinks for the MOSFETs while also reducing the amount of input power required, allowing for a lower-capacity power supply design. Therefore, class-D amplifiers are typically smaller than an equivalent class-AB amplifier.

Another advantage of the class-D amplifier is that it can operate from a digital signal source without requiring a digital-to-analog converter (DAC) to convert the signal to analog form first. If the signal source is in digital form, such as in a digital media player or computer sound card, the digital circuitry can convert the binary digital signal directly to a pulse-width modulation signal that is applied to the amplifier, simplifying the circuitry considerably and reducing opportunities for noise ingress.

A class-D amplifier with moderate output power can be constructed using regular CMOS logic process, making it suitable for integration with other types of digital circuitry. Thus it is commonly found in System-on-Chips with integrated audio when the amplifier shares a die with the main processor or DSP.

While class-D amplifiers are widely used to control motors, they are also used as power amplifiers. Though if the signal is not already in a pulse modulated format prior to amplification, it must first be converted, which may require additional circuitry. Switching power supplies have even been modified into crude class-D amplifiers (though typically these only reproduce low-frequencies with acceptable accuracy).

High-quality class-D audio power amplifiers are readily available on the market. Dynamic range of 118 dB in a high-end consumer product was seen in the year 2009. Most, however, remain closer to 100 dB dynamic range at this time [2022] due to practical cost considerations. These designs have been said to rival traditional class A and AB amplifiers in terms of quality. An early use of class-D amplifiers was high-power subwoofer amplifiers in cars. Because subwoofers are generally limited to a bandwidth of no higher than 150 Hz, switching speed for the amplifier does not have to be as high as for a full range amplifier, allowing simpler designs. Class-D amplifiers for driving subwoofers are relatively inexpensive in comparison to class-AB amplifiers.

The letter D used to designate this amplifier class is simply the next letter after C and, although occasionally used as such, 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 analog signal. (A digital waveform would be pulse-code modulated.)

Additional classes

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Other amplifier classes are mainly variations of the previous classes. For example, class-G and class-H amplifiers are marked by variation of the supply rails (in discrete steps or in a continuous fashion, respectively) following the input signal. Wasted heat on the output devices can be reduced as excess voltage is kept to a minimum. The amplifier that is fed with these rails itself can be of any class. These kinds of amplifiers are more complex, and are mainly used for specialized applications, such as very high-power units. Also, class-E and class-F amplifiers are commonly described in literature for radio-frequency applications where efficiency of the traditional classes is important, yet several aspects deviate substantially from their ideal values. These classes use harmonic tuning of their output networks to achieve higher efficiency and can be considered a subset of class C due to their conduction-angle characteristics.

Class E

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The class-E amplifier is a highly efficient tuned switching power amplifier used at radio frequencies. It uses a single-pole switching element and a tuned reactive network between the switch and the load. The circuit obtains high efficiency by only operating the switching element at points of zero current (on to off switching) or zero voltage (off to on switching) which minimizes power lost in the switch, even when the switching time of the devices is long compared to the frequency of operation.[22]

The class-E amplifier is frequently cited to have been first reported in 1975.[23] However, a full description of class-E operation may be found in the 1964 doctoral thesis of Gerald D. Ewing.[24] Interestingly, analytical design equations only recently became known.[25]

Class F

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In push–pull amplifiers and in CMOS, the even harmonics of both transistors just cancel. Experiment shows that a square wave can be generated by those amplifiers. Theoretically square waves consist of odd harmonics only. In a class-D amplifier, the output filter blocks all harmonics; i.e., 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 the 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 in class-D, transistors and the load exist as two separate modules, 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.[26] Of course there must 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 overswing of the voltage square wave. A class-F load network by definition has to transmit below a cutoff frequency and reflect above.

Any frequency lying below the cutoff and having its second harmonic above the cutoff can be amplified, that is an octave bandwidth. On the other hand, an inductive-capacitive series circuit with a large inductance and a tunable capacitance may be simpler to implement. By reducing the duty cycle below 0.5, the output amplitude can be modulated. The voltage square waveform degrades, 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 inductor 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.

Classes G and H

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Idealized class-G rail voltage modulation
Idealized class-H rail voltage modulation
Rail voltage modulation
Basic schematic of a class-H configuration

There are a variety of amplifier designs that enhance class-AB output stages with more efficient techniques to achieve greater efficiency with low distortion. These designs are common in large audio amplifiers since the heatsinks and power transformers would be prohibitively large (and costly) without the efficiency increases. The terms "class-G" and "class-H" are used interchangeably to refer to different designs, varying in definition from one manufacturer or paper to another.

Class-G amplifiers (which use "rail switching" to decrease power consumption and increase efficiency) are more efficient than class-AB amplifiers. These amplifiers provide several power rails at different voltages 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-G amplifiers are more efficient than class AB but less efficient when compared to class-D. However, they do not have the electromagnetic interference effects of class D.

Class-H amplifiers create an infinitely variable (analog) supply rail. They are sometimes referred to as rail trackers. This is done by modulating the supply rails so that the rails are only a few volts larger than the output signal "tracking" it at any given time. The output stage operates at its maximum efficiency all the time. This is due to the circuit ability to keep the rail transistors (T2 and T4) in cutoff until a music voltage peak is of a sufficient magnitude to require the additional voltage from the + and - 80 V supplies. Refer to the schematic figure. The class H amplifier can actually be thought of as two amplifiers in series. In the schematic example shown by the figure, +/- 40 V rail amplifiers can produce about 100 watts continuous into an 8-ohm load. If the output signal is operating below 40 volts, the amplifier only has the losses associated with a 100 W amplifier. This is because the class-H upper devices T2 and T4 are only used when the music signal is between 100 and 400 watts output. The key to understanding this efficiency without churning the actual numbers is that we have a 400-watt-capable amplifier but with the efficiency of a 100-watt amplifier. This is because the waveforms of music contain long periods under 100 watts and contain only brief bursts of up to 400 watts – in other words, the losses at 400 watts are for brief time periods. If this example were drawn as a class AB with just the 80 V supplies in place of the 40 V supplies, the T1 and T3 transistors would need to be in conduction throughout the 0 V to 80 V signal with the corresponding losses all through the wave period - not just the brief high energy bursts. To achieve this rail tracking control, T2 and T4 act as current amplifiers, each in series with its low voltage counterpart T1 and T3. The purpose of T2 and T3 is to allow back-biasing diode D2 when the amplifier output is at a positive peak (above 39.3 V) and back biasing D4 when the output is at negative peak less than -39.3 V. During the musical peaks from 100 to 400 watts, the +/-40 V rails source no current as all the current comes from the +/-80 V rails. This figure is too simplistic, however, as it will not actually control the T2 and T4 transistors at all. This is because the D1 and D3 diodes which are intended to provide a path for the output voltage back into the upper devices are always reverse biased. They are drawn backwards. In place of these diodes, a voltage amplifier with gain which uses vout as its input would be needed in an actual design. There is another reason for this gain requirement between vout and T2 base in an actual class-H design and that is to assure that the signal applied to the T2 is always "ahead" of the Vout signal so it can never "catch up" with the rail tracker. The rail tracker amplifier might have a 50 V/μs slew rate while the class-AB amplifier might have only a 30 V/μs slew rate in order to guarantee this.

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Power amplifier classes

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Power amplifier classes are letter designations (such as A, B, AB, C, D, E, F, G, and H) used to categorize electronic power amplifiers based on their circuit configuration, conduction angle of active devices relative to the input signal cycle, and resulting trade-offs between , , and . These classifications primarily apply to amplifiers in audio, (RF), and other signal amplification applications, where the goal is to deliver high output power to a load while minimizing losses and maintaining signal fidelity. The most fundamental classes focus on linear operation: Class A amplifiers conduct for the entire input cycle, providing the highest linearity but with maximum theoretical efficiency of 50% (practical often ≤25%), making them suitable for applications requiring low distortion like high-fidelity audio. Class B amplifiers use push-pull configurations where each device conducts for half the cycle, achieving up to 78.5% efficiency but introducing crossover distortion at the zero-crossing point, which limits their use in precise linear applications. Class AB serves as a compromise, with devices biased to conduct slightly more than half the cycle (near pinch-off, often 10-15% of maximum current), balancing efficiency (between 50% and 78.5%) and reduced distortion for widespread use in audio power amplifiers. Non-linear and switching classes prioritize efficiency for high-power, narrowband, or RF scenarios: Class C conducts for less than half the cycle and requires tuned circuits for output filtering, offering theoretical up to 100% (practical <100%) but poor linearity, ideal for constant-envelope signals like FM modulation. Class D employs (PWM) with switching transistors operating as on/off devices, achieving efficiencies over 90% through minimized conduction losses, commonly used in modern audio systems and portable devices. Advanced variants like Class E and Class F use harmonic tuning networks to shape voltage and current waveforms for near-100% , with Class E focusing on zero-voltage switching ( ≤94%) and Class F on square-like waveforms (≤88.4%), both prevalent in RF transmitters. Classes G and H enhance via dynamic supply voltage modulation or multiple power rails, reducing dissipation in high-power audio and broadcast amplifiers. Overall, the choice of power amplifier class depends on application demands— for signals (e.g., AM, SSB) versus efficiency for power-constrained or high-output systems (e.g., cellular base stations, wireless communications)—with ongoing advancements in hybrid designs and techniques addressing traditional trade-offs.

Fundamentals

Classification principles

Power amplifiers are electronic circuits designed to increase both the voltage and current of an input signal to deliver significant output power to demanding loads, such as loudspeakers, antennas, or transmitters, in contrast to small-signal amplifiers that primarily handle low-power signals for processing or intermediate stages without substantial power delivery. This distinction arises because power amplifiers must manage high currents and voltages, often exceeding 200 mA peak AC current, to achieve the necessary drive capability while maintaining under load. The classification system for power amplifiers originated in the early amid the development of technology for radio transmission and reception, where early designs focused on balancing power output with thermal management in tube-based circuits. Formal letter-based designations, such as Classes A, B, and C, were established in through contributions in radio literature, providing a standardized framework for describing operational modes. With the invention of the in and its commercialization in the , these principles evolved to solid-state implementations, enabling compact, efficient designs while retaining the core classification concepts. The fundamental criterion for classification is the conduction angle of the output devices, which measures the fraction of the input signal's cycle—typically a sinusoidal —during which the active devices (tubes or transistors) conduct significant current. A conduction of 360° indicates full-cycle operation, where the device remains active throughout the entire period, whereas angles less than 360°, such as 180° or below, represent partial conduction limited to specific portions of the cycle. This is determined by the biasing point relative to the signal , influencing trade-offs in performance. Power amplifiers are generally grouped into linear modes, which maintain a proportional relationship between input and output for accurate signal reproduction; nonlinear modes, which allow distortion to prioritize through partial conduction or utilization; and switching modes, which operate the devices as on-off switches using techniques like to minimize power loss. and serve as primary metrics for evaluating these modes, though their detailed quantification varies by application. A representative illustrates this with a sinusoidal input signal overlaid on the device's transfer characteristic, where the bias point is marked on the quiescent operating line, and conduction periods are highlighted as shaded arcs spanning the defined angle around the peaks, demonstrating how reduced conduction narrows the for higher at the cost of .

Key metrics and trade-offs

Efficiency in power amplifiers is defined as the of output power to input power, expressed as η=PoutPin×100%\eta = \frac{P_{out}}{P_{in}} \times 100\%. This metric quantifies how effectively the amplifier converts supplied electrical power into useful output signal power, with theoretical maximum values varying by design; for instance, a typical linear configuration achieves up to 25% under resistive . refers to the amplifier's ability to produce an output signal proportional to the input without introducing unwanted distortions, primarily assessed through (THD) and distortion (IMD). THD measures the of the root-mean-square value of content to the fundamental signal, often expressed in or decibels, capturing nonlinear effects that generate harmonics. IMD evaluates distortion from multiple input tones, where nonlinearities create sum and difference frequencies, quantified similarly by comparing distortion products to the fundamental amplitudes. plays a critical role in , as insufficient can push the amplifier into or saturation regions, exacerbating and degrading signal fidelity across the conduction angle. Heat dissipation arises from power losses in the amplifier, calculated as Ploss=Pin−PoutP_{loss} = P_{in} - P_{out}, representing converted to output rather than signal power. Effective management, including heatsinks and cooling systems, is essential to prevent device overheating, which can reduce lifespan, alter performance, or cause failure, particularly in high-power applications where losses scale with input levels. A fundamental trade-off exists between efficiency and linearity: achieving high linearity typically requires operating points that maintain devices in their linear region, leading to continuous power draw and lower efficiency, while prioritizing efficiency often involves nonlinear operation that increases distortion. For example, designs optimized for minimal distortion may sacrifice up to 75% of input power to heat, whereas those emphasizing efficiency might tolerate higher THD levels to approach theoretical maxima near 80%. Bandwidth and gain further complicate these metrics in power amplifiers, where sufficient voltage or power gain must be maintained over the operational frequency range without compromising efficiency or linearity, often limited by device parasitics and stability constraints.

Linear Classes

Class A

Class A amplifiers operate with output devices that conduct throughout the entire 360° cycle of the input signal, ensuring the or tube remains biased in the at the quiescent point for maximum . This full conduction angle means the device draws a constant current even in the absence of an input signal, with the output current varying sinusoidally around this quiescent value while always remaining positive and never reaching zero. The biasing is typically set at the of the load line to allow symmetric signal swings without clipping, resulting in an amplified output that closely replicates the input with minimal . A typical Class A transistor amplifier uses a common-emitter configuration with voltage divider biasing to achieve stable operation. The resistors include R1 and R2, which form the voltage divider to set the base voltage VBV_B; RE, the emitter resistor for negative feedback and thermal stabilization; and RL, the collector load resistor. To determine optimal values for maximum efficiency and linearity while avoiding distortion, follow these steps: First, select RL based on desired output power, then set the quiescent collector current ICQ≈VCC2RLI_{CQ} \approx \frac{V_{CC}}{2 R_L} to allow maximum symmetric voltage swing without clipping. Next, choose RE such that the emitter voltage VE=ICQ⋅REV_E = I_{CQ} \cdot R_E, typically with RE providing a voltage drop of about 1-10% of V_CC for stability (e.g., RE = \frac{V_{CC}/10}{I_{CQ}}). The base voltage is then VB=VE+VBEV_B = V_E + V_{BE}, where VBE≈0.7V_{BE} \approx 0.7 V for silicon transistors. For the voltage divider, set VB=VCC⋅R2R1+R2V_B = V_{CC} \cdot \frac{R_2}{R_1 + R_2}, choosing R1 and R2 with a parallel combination R1∥R2≤βRE10R_1 \parallel R_2 \leq \frac{\beta R_E}{10} (where β is the transistor's current gain) to ensure a stiff bias network that minimizes variations due to β or temperature. This biasing ensures the transistor operates at the midpoint of the load line, maximizing linearity and efficiency within the 25% limit for resistive loads. The of Class A amplifiers is inherently low due to the continuous power dissipation in the output devices. For a resistive load (series-fed configuration), the maximum theoretical is 25%, derived from the ratio of maximum AC output power to DC input power. The DC input power is PDC=VCCIDQP_{DC} = V_{CC} I_{DQ}, where IDQ=VCC2RLI_{DQ} = \frac{V_{CC}}{2R_L} for optimal biasing, yielding PDC=VCC22RLP_{DC} = \frac{V_{CC}^2}{2R_L}. The maximum output power occurs at peak voltage swing Vp=VCC2V_p = \frac{V_{CC}}{2}, giving Pout=Vp22RL=VCC28RLP_{out} = \frac{V_p^2}{2R_L} = \frac{V_{CC}^2}{8R_L}. Thus, η=PoutPDC=VCC2/8RLVCC2/2RL=25%\eta = \frac{P_{out}}{P_{DC}} = \frac{V_{CC}^2 / 8R_L}{V_{CC}^2 / 2R_L} = 25\%. In transformer-coupled designs, which use inductive loads to separate DC and AC paths, the maximum improves to 50% by allowing larger voltage swings without increasing DC power dissipation. Practical efficiencies are often lower, around 20-40%, due to losses in components. Advantages of Class A amplifiers include exceptional and very low (THD typically below 0.1%), making them ideal for high-fidelity audio applications where signal purity is paramount. They eliminate entirely since the output devices never turn off, providing smooth waveform reproduction without the need for complex feedback circuits. However, these benefits come at the cost of high generation from constant quiescent current, necessitating large heatsinks and robust power supplies, which increase size, weight, and operational costs. The low efficiency also limits their use in high-power scenarios, as much of the input power is dissipated as rather than delivered to the load. Common implementations include single-ended configurations using one active device for simple, low-power designs, and push-pull setups with complementary devices for higher output while maintaining full conduction. vacuum tube variants are particularly favored in audio for their "warm" , characterized by predominantly even-order harmonics that add a pleasing euphonic quality to reproduction. Historically, Class A amplifiers dominated early high-fidelity systems in the mid-20th century due to their superior , and they remain popular in 2025 boutique audio designs for audiophiles seeking uncompromised quality despite the inefficiencies.

Class B

Class B amplifiers operate using a with complementary active devices, such as an NPN and a PNP bipolar junction transistor (BJT), each conducting for exactly 180° of the input signal cycle. One device handles the positive half-cycle by sourcing current to the load, while the other manages the negative half-cycle by sinking current, with no conduction overlap. The devices are biased at zero volts at the point, ensuring minimal quiescent current when no signal is present. The theoretical maximum efficiency of a Class B amplifier reaches 78.5%, significantly higher than the 50% limit of Class A amplifiers, due to the halved conduction time per device. This value derives from the ratio of average output power to average supply power for a sinusoidal input. For a resistive load RLR_L and supply voltage VCCV_{CC}, the peak output current is Ip=VCC/RLI_p = V_{CC}/R_L (neglecting saturation voltage), yielding average output power Pout=Ip2RL/2=VCC2/(2RL)P_{out} = I_p^2 R_L / 2 = V_{CC}^2 / (2 R_L). The average supply current is Iavg=Ip/πI_{avg} = I_p / \pi, so supply power Psupply=2VCCIavg=2VCC2/(πRL)P_{supply} = 2 V_{CC} I_{avg} = 2 V_{CC}^2 / (\pi R_L). Thus, η=Pout/Psupply=(π/4)×100%≈78.5%\eta = P_{out} / P_{supply} = (\pi / 4) \times 100\% \approx 78.5\%, achieved at maximum output swing. While offering improved efficiency, Class B amplifiers introduce near the zero-crossing of the output waveform, arising from a "dead zone" where neither device conducts—typically 1.2 to 1.4 V wide due to the ~0.7 V base-emitter drop of each BJT—resulting in a flattened response and nonlinear behavior. This generates primarily odd-order harmonics but can also produce even-order harmonics if the push-pull symmetry is imperfect. A basic circuit example is a complementary emitter-follower stage using matched NPN (e.g., ) and PNP (e.g., ) transistors with their bases driven by the input signal, emitters connected to the load via small resistors (e.g., 1.1 Ω) for stability, and collectors tied to the supply rails, operating without in its simplest form. Class B amplifiers find applications in medium-power audio systems, such as portable devices or broadcast equipment, where efficiency is prioritized over absolute to minimize heat dissipation and power consumption without excessive complexity. To mitigate and content, these amplifiers often incorporate in practical designs, though the inherent base configuration remains susceptible to even-order generation without such compensation.

Class AB

Class AB amplifiers represent a hybrid approach between Class A and Class B configurations, where the active devices are biased slightly above their cutoff point to conduct for more than 180° but less than 360° of the input signal cycle, thereby minimizing the crossover distortion inherent in pure Class B operation while preserving higher efficiency than Class A. This partial conduction ensures that both devices in a push-pull stage remain active near the zero-crossing of the signal, smoothing transitions and enhancing for applications requiring faithful signal reproduction. The efficiency of Class AB amplifiers typically ranges from 50% to 78.5% theoretically, with practical values often around 50-60% depending on the bias current setting, which allows designers to between distortion reduction and power dissipation. Higher bias currents approach Class A performance with lower efficiency, while lower biases lean toward Class B's higher efficiency but risk increased . These amplifiers exhibit low when combined with circuits, making them suitable for high-fidelity audio reproduction, and they remain prevalent in modern home stereo power amplifiers as of 2025 due to their balance of sound quality and thermal management. in Class AB stages is commonly achieved using Vbe multiplier circuits or strings to provide a stable that compensates for variations in the output transistors, ensuring thermal stability and preventing runaway conditions. The Vbe multiplier, essentially a transistor-based , adjusts the quiescent current dynamically to maintain optimal operation across varying loads and s. Key advantages include substantial power output capability with moderate heat generation compared to Class A, alongside improved over Class B, though challenges arise from potential drift if thermal compensation is inadequate, which can lead to or inefficiency. Since the transistor era's advent in the mid-20th century, Class AB has become the standard for linear power amplification, with ongoing refinements in and integration enabling its adaptation to low-power portable devices where efficiency constraints demand careful optimization without sacrificing audio performance.

Nonlinear Classes

Class C

Class C amplifiers operate with a conduction angle less than 180 degrees, typically around 90 to 120 degrees, where the active device is biased below its point, resulting in short current pulses that amplify only the positive peaks of the input signal. This ensures the transistor conducts for a brief portion of the RF cycle, producing a highly nonlinear response with significant distortion. Unlike linear classes, the output is restored to a near-sinusoidal shape by a resonant tank circuit, which filters out higher-order harmonics and selects the component. The of Class C amplifiers can reach up to 90% when paired with a resonant load, far surpassing linear classes due to the reduced average current draw from the short conduction periods. Theoretical can approach 100% as the conduction angle decreases, though output power diminishes; practical efficiencies of 80-90% are typical. However, this high comes at the cost of poor and high , rendering Class C unsuitable for audio amplification or signals where is required. In RF applications, the tuned circuit effectively suppresses harmonics, mitigating for operation. Typical circuits for Class C amplifiers are single-ended configurations featuring a with a tuned LC tank circuit at the output to restore the and match the load impedance. These are commonly employed in RF power stages, such as FM transmitters and historical AM radio systems, where high efficiency is prioritized over for constant-envelope signals like FM or CW. Despite their advantages, Class C amplifiers suffer from narrow bandwidth due to the frequency-specific tuning of the resonant circuit, necessitating retuning for different operating frequencies and limiting their use to fixed or slowly varying carrier signals. This makes them less versatile for modern wideband applications compared to more advanced classes.

Tube amplifier suffixes

In vacuum tube power amplifiers, particularly those operating in RF applications, a suffix system is used with class designations to indicate specific operating conditions related to grid current. This system originated in the early to standardize designs for high-efficiency amplification in transmitters. Standard class C denotes conduction less than 180 degrees of the input cycle. Common suffixes include "1" for operation without grid current during any part of the input cycle and "2" for operation where grid current flows during part of the cycle, allowing for different and drive conditions. Operation of these tube classes relies on resonant tuned circuits that selectively suppress unwanted harmonics, enabling shaping that boosts beyond 80%—with class C variants approaching 90% under optimal conditions—while maintaining sufficient linearity for RF signals. For instance, in class C, the tube conducts briefly per cycle, minimizing power dissipation in the device, and external tuning circuits filter the output to reconstruct the desired . This approach contrasts with linear classes by prioritizing over full-cycle fidelity, making it ideal for constant-envelope signals in RF power stages. Historically, these class C tube amplifiers played a pivotal role in radar systems and transmitters, where high-power RF generation at efficiencies up to 85% was critical for reliable long-range communication and detection. Post-transistor era, their use declined due to solid-state alternatives, but they have seen revival in niche high-power RF applications, including 2025 setups employing tubes like the GS-35b for VHF amplification exceeding 1 kW, often in linear configurations. Compared to solid-state designs, tube variants operate at much higher voltages—often thousands of volts—necessitating robust insulation and transformers, while inter-electrode capacitances in the tube structure influence harmonic tuning and require careful neutralization to prevent oscillation. In modern contexts, hybrid configurations combining tube output stages with solid-state drivers and power supplies have emerged for high-power RF needs, offering the warmth and high-voltage handling of tubes alongside the reliability and compactness of semiconductors in applications like broadcasting and defense.

Switching Classes

Class D

Class D amplifiers are switching-mode power amplifiers that achieve high by operating output transistors as binary switches, either fully on or fully off, with no time spent in the linear conduction region. This corresponds to conduction angles of 0° (off) or 360° (on) during each switching cycle, contrasting with linear amplifier classes. The input analog signal is first converted into a digital train using techniques such as (PWM) or (PDM); in PWM, the width of fixed-frequency varies with the signal , while in PDM, the density of at a constant width encodes the . These drive a power stage, typically configured as a half-bridge or full-bridge topology with MOSFETs or other switches, generating a high-frequency square-wave output at carrier frequencies ranging from 250 kHz to 1.5 MHz. A low-pass output filter then reconstructs the original low-frequency signal by attenuating the carrier and its harmonics, ensuring the load receives a clean analog waveform. The efficiency of Class D amplifiers stems from the absence of voltage-current overlap in the linear region, theoretically approaching 100% as power dissipation occurs primarily during switching transitions rather than continuous conduction. In practice, efficiencies exceed 90% at typical audio power levels, such as 14 W into 8 Ω loads, with minimal heat generation due to low on-resistance losses and reduced quiescent power. The efficiency can be approximated as η≈100%−switching losses,\eta \approx 100\% - \text{switching losses}, where switching losses include those from transistor turn-on/off times, gate drive, and dead-time effects, often resulting in real-world figures of 80–95% depending on load and frequency. Key characteristics of Class D amplifiers include low when properly designed, with (THD) minimized through feedback loops and precise filtering; output filters, often LC networks tuned to the carrier frequency, effectively remove high-frequency components to prevent and ensure . However, improper filtering can introduce ripple or . Variants like PWM offer straightforward implementation with fixed carrier frequencies for stable filtering, whereas PDM provides finer resolution at high densities, suitable for digital inputs like DSD audio, though it may require higher rates. Advantages of Class D designs include their compact size and cool operation, as high efficiency eliminates the need for large heatsinks, enabling smaller form factors ideal for integration. Drawbacks encompass from fast switching edges, necessitating shielding and spread-spectrum techniques, as well as added complexity from output filters that increase component count and cost. Class D amplifiers find widespread use in audio applications such as subwoofers, portable speakers, and , where their efficiency supports battery-powered devices, as well as in motor drives for electric vehicles and due to precise PWM control of . By 2025, advancements in (GaN) transistors have elevated their audio performance, with implementations achieving 70% lower THD and 5% higher efficiency compared to silicon-based designs, rivaling the fidelity of traditional Class AB amplifiers while maintaining compact, high-power outputs up to 1500 W.

Class E

Class E power amplifiers are high-efficiency switching amplifiers designed primarily for radio-frequency (RF) applications, where the active device operates as an on/off switch rather than in its linear region. Introduced by Nathan O. Sokal and Alan D. Sokal in 1975, this class achieves minimal power dissipation by ensuring the switch voltage is zero and its derivative is zero at turn-on, preventing overlap between voltage and current waveforms. The resonant load network shapes the current and voltage across the switch to realize zero-voltage switching (ZVS), which significantly reduces switching losses compared to linear classes like A, B, or C. In operation, the switches at the zero-voltage point of its waveform, with the shunt discharging during the off-state to build voltage gradually, avoiding abrupt transitions that cause . The load network—a series , , and tuned —provides a reactive path that aligns the component with the desired output while suppressing harmonics. This nonlinear operation results in no overlap between significant voltage and current, enabling theoretical approaching 100%, with practical implementations often exceeding 90%. Design equations for the load network ensure these conditions; for example, the shunt C1C_1 is given by C1=0.18362πfRC_1 = \frac{0.1836}{2\pi f R}, where ff is the operating and RR is the load resistance, facilitating explicit calculation of component values for optimal performance. Key characteristics include operation due to the tuned load, making it suitable for fixed-frequency applications, and low component stress from the sinusoidal-like waveforms at the switch. The design is insensitive to small variations in component values, and simulations must account for harmonic content generated by the nonlinear switching, often requiring for accurate modeling. Compared to Class D amplifiers, which share a switching principle but typically use , Class E offers reduced switching losses at high frequencies (above several MHz) through its ZVS and zero-derivative conditions, enabling operation up to bands. Applications of Class E amplifiers include RF transmitters for wireless communications, where their efficiency supports power-constrained systems, and systems operating at frequencies like 13.56 MHz. Developed in the , they remain popular in 2025 for mobile base stations, particularly in and LTE/ edge amplifiers, due to their ability to deliver high output power with minimal heat dissipation in GaN or technologies. The basic circuit employs a single , RF choke for DC supply, shunt , and tuned LC load network to deliver sinusoidal output to the antenna or load.

High-Efficiency Classes

Class F

Class F power amplifiers achieve high by employing a load network that shapes the drain voltage into a square-like form through precise control of impedances. The output matching network is designed to present low impedance (ideally a ) at even harmonics and (ideally an open circuit) at odd harmonics of the . This tuning minimizes the overlap between the voltage and current , reducing power dissipation in the . The voltage approximates a square wave, while the current remains a half-sine, enabling operation beyond traditional linear classes. Theoretically, Class F amplifiers can attain 100% when an infinite number of harmonics are controlled, as the square voltage allows all DC power to be converted to RF output without loss. In practice, with finite harmonics—typically the second and third—efficiencies reach 80-90%, depending on the implementation. An important variant is the inverse Class F amplifier, which inverts the shaping strategy by presenting at even harmonics and low impedance at odd harmonics, resulting in a square-like current and a half-sinusoidal voltage . This approach also targets near-100% theoretical and offers similar practical performance, with the choice between Class F and inverse Class F often depending on device characteristics and requirements. Both modes support operation when limited to finite harmonics, though full requires more complex tuning. Class F amplifiers are widely applied in high-power RF systems, such as broadcast transmitters and base stations, where their reduces thermal management needs and improves energy utilization. For instance, GaN-based Class F designs operate effectively in sub-6 GHz bands, delivering tens of watts with efficiencies above 70%. This class extends historical tube amplifier techniques—originally using tuning for in devices—to modern solid-state implementations, enhancing scalability in solid-state RF power. Design of Class F amplifiers centers on multi-harmonic resonators, such as quarter-wave stubs or lumped LC networks, to synthesize the required impedances across frequencies. These resonators control up to the third or fifth for practicality, but adding more increases at the cost of bandwidth, creating a key : narrower operation for higher peak versus broader tuning for applications like wideband . Load-pull simulations and analysis are essential to optimize these networks. Historically, Class F concepts evolved from early 20th-century tube amplifier experiments with harmonic peaking, gaining prominence in the for RF broadcast before solid-state adaptation in the and . Seminal work formalized the maximally flat approach, paving the way for integration into advanced architectures like Doherty amplifiers, where Class F or inverse Class F stages enhance back-off efficiency in modern wireless systems.

Classes G and H

Classes G and H represent hybrid linear amplifier designs that enhance the efficiency of Class AB amplifiers through dynamic modulation, reducing wasted energy in the output stage while preserving low characteristics. These classes switch or track the supply voltage to closely follow the signal , minimizing the voltage across the output transistors during operation and thereby lowering . Unlike fixed-supply amplifiers, they engage higher voltages only as needed for signal peaks, making them suitable for applications demanding and power without excessive heat. Class G amplifiers operate using multiple fixed supply rails, typically two or more pairs of positive and negative voltages (e.g., ±35 V for low levels and ±70 V for peaks), with the output stage transistors connected via diodes or switches to select the appropriate rail based on the instantaneous signal amplitude. For signals below a threshold, the inner low-voltage transistors conduct using the lower rail, reducing power loss as the supply closely matches the output requirements; when the signal exceeds this threshold, outer high-voltage transistors activate to handle peaks, with commutation occurring seamlessly to avoid clipping. This conduction pattern mirrors Class AB biasing but achieves greater efficiency by limiting unnecessary high-voltage exposure. Rail transitions are managed to minimize losses, such as resistive heating Ploss=I2RP_{\text{loss}} = I^2 R during switching, through careful timing and feedback. Class H amplifiers build on this principle with a continuously variable supply that modulates in real-time with the audio signal , often implemented via tracking regulators or modulated boost converters rather than discrete rails. The power supply voltage dynamically adjusts to remain slightly above the peak output requirement, eliminating the stepped transitions of Class G and further optimizing voltage headroom. This envelope-tracking approach ensures the output stage operates with minimal drop across the transistors, maintaining linear amplification while adapting to varying signal demands. Efficiency in Classes G and H typically ranges from 80% to 90% at peak output, a marked improvement over Class AB's 50-70%, particularly at moderate power levels where fixed supplies waste on quiescent and low-signal operation. For instance, a Class G design can achieve 87% efficiency at 0.4-0.5 W output into an 8 Ω load, extending battery life in portable systems by up to 10% compared to fixed-boost alternatives. Class H often sustains higher average efficiency across a broader due to its continuous modulation, though it requires more sophisticated control to avoid ripple. These amplifiers exhibit low distortion levels when negative feedback is applied around the output stage, comparable to Class AB, but their complexity arises from the additional switching or tracking circuitry, which can introduce challenges in stability and transient response. Proper design mitigates issues like crossover distortion at rail transitions through predictive signal processing or soft-switching techniques. In applications, Classes G and H are favored in equipment, such as high-power public address systems and live sound reinforcement, where outputs exceed 200 W per channel; as of 2025, they enable energy-efficient deployments in touring rigs and studio monitors by reducing thermal management needs. They also appear in battery-powered portable devices, like smartphones and , to maximize playtime without compromising audio quality. The primary advantages include delivering high output power with significantly less heat dissipation—potentially halving thermal output compared to Class AB for the same load—allowing for compact designs with smaller heatsinks and transformers. This efficiency gain supports longer operation in power-constrained environments. However, disadvantages encompass increased and cost from the rail-switching or modulation components, as well as potential switching or glitches if transitions are not perfectly managed, which can affect audio purity in high-fidelity setups. A key distinction lies in their supply modulation: Class G relies on discrete stepped rails for simplicity in implementation, while Class H employs continuous tracking for smoother efficiency profiles and reduced transition artifacts.
AspectClass GClass H
Supply TypeMultiple fixed rails (e.g., 2-3 levels)Continuously variable tracking
ModulationDiscrete switching at thresholdsReal-time envelope following
Peak EfficiencyUp to 87% at moderate power80-90% sustained across range
ComplexityModerate (rail selectors)Higher (regulators/boost)
Typical UsePro audio, high-power PAPortable, dynamic-range audio

References

  1. https://vtechworks.lib.vt.edu/bitstreams/ef5685a4-7077-4725-a2d9-6224438f1d7a/download
  2. https://people.engr.tamu.edu/spalermo/ecen326/lecture08_ee326_output_stages.pdf
  3. https://www.analog.com/en/resources/glossary/power-amplifier.html
  4. https://www.allaboutcircuits.com/technical-articles/introduction-to-rf-class-a-power-amplifiers/
  5. https://www.highfrequencyelectronics.com/May10/HFE0510_Grebennikov_Part1.pdf
  6. https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/Technology-Radio/Radio-Engineering-Terman-2nd-1937.pdf
  7. https://spectrum.ieee.org/the-lost-history-of-the-transistor
  8. https://www.analog.com/en/resources/analog-dialogue/articles/confused-about-amplifier-distortion-specs.html
  9. https://ieeexplore.ieee.org/document/1261285
  10. https://www.electronics-tutorials.ws/amplifier/amplifier-classes.html
  11. https://resources.altium.com/p/know-power-dissipation
  12. https://www.ti.com/sc/docs/msp/papers/1998/nossaman.pdf
  13. https://www.tandfonline.com/doi/pdf/10.1080/00207210802526562
  14. https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electronics/Microwave_and_RF_Design_V%3A_Amplifiers_and_Oscillators_(Steer)/02%3A_Linear_Amplifiers/2.05%3A_Class_A_AB_B_and_C_Amplifiers
  15. https://www.electronics-tutorials.ws/amplifier/amp_5.html
  16. https://www.tutorialspoint.com/amplifiers/transformer_coupled_class_a_power_amplifier.htm
  17. https://www.audiotechnology.com/tutorials/view-from-the-bench-amplifier-class-wars
  18. https://www.effectrode.com/knowledge-base/the-cool-sound-of-tubes/
  19. https://wiki.analog.com/university/courses/engineering_discovery/lab_14
  20. https://www.allaboutcircuits.com/technical-articles/introduction-to-class-b-power-amplifiers/
  21. https://pages.hmc.edu/mspencer/e151/sp24/notes/22.pdf
  22. https://www.electro-tech-online.com/threads/class-b-distortion-harmonics.118039/
  23. https://www.soundbridge.io/class-b-amplifier
  24. https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electronics/Microwave_and_RF_Design_V%253A_Amplifiers_and_Oscillators_%28Steer%29/02%253A_Linear_Amplifiers/2.05%253A_Class_A_AB_B_and_C_Amplifiers
  25. https://www.analog.com/en/resources/technical-articles/types-of-audio-amplifiers.html
  26. https://www.electronics-lab.com/article/class-ab-amplifiers/
  27. https://www.ti.com/lit/pdf/snaa128
  28. https://hifibuys.com/class-a-b-amplifiers-the-sweet-spot-between-sound-quality-and-efficiency/
  29. http://www.engr.newpaltz.edu/~zunoubm/S20/electronics2/Lecture_Notes/Power%2520Amps/Uses_This_Electronics_Ch13.pdf
  30. https://www.electronics-tutorials.ws/amplifier/class-ab-amplifier.html
  31. https://www.allaboutcircuits.com/technical-articles/introduction-to-the-class-c-power-amplifier/
  32. https://web.ece.ucsb.edu/~long/ece145b/PA_notes3.pdf
  33. https://totalelectricaltraining.co.uk/understanding-class-c-amplifiers-applications-advantages-and-limitations/
  34. https://www.highfrequencyelectronics.com/Sep08/HFE0908_Grebennikov.pdf
  35. https://www.worldradiohistory.com/Archive-Courses/NRI-1976-Single-Lesson-Class-C-Power-Amps-AM-Radio.pdf
  36. https://ham-amplifiers.com/en/gs-35-vacuum-tube-power-amplifier-for-vhf-high-power-amateur-radio-amplifier
  37. https://www.rfecho.com/solid-state-power-amplifier-vs-traditional-amplifiers-whats-the-difference/
  38. https://www.photonisdefense.com/Power-and-Microwave
  39. https://www.analog.com/en/resources/technical-articles/fundamentals-of-class-d-amplifiers.html
  40. https://www.allaboutcircuits.com/technical-articles/introduction-to-switching-mode-power-amplifiers-class-d-operation/
  41. https://www.arylic.com/blogs/news/class-d-amplifier
  42. https://www.infineon.com/dgdl/an-1071.pdf?fileId=5546d462533600a40153559538eb0ff1
  43. https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/6/A-comprehensive-study-of-class-D-amplifier-technology.pdf
  44. https://icepoweraudio.com/introduction-to-class-d-audio-amplification/
  45. https://www.analog.com/en/resources/analog-dialogue/articles/class-d-audio-amplifiers.html
  46. https://epc-co.com/epc/about-epc/events-and-news/news/artmid/1627/articleid/3168/design-high-performance-class-d-audio-amplifiers-with-gan-fets
  47. https://www.infineon.com/market-news/2025/infpss202502-061
  48. https://people.physics.anu.edu.au/~dxt103/160m/class_E_amplifier_design.pdf
  49. https://www.allaboutcircuits.com/technical-articles/unraveling-the-design-equations-of-the-class-e-power-amplifier/
  50. https://www.allaboutcircuits.com/technical-articles/introduction-to-the-class-e-power-amplifier/
  51. https://www.researchgate.net/publication/256086387_Class-E_Amplifier_Design_Improvements_for_GSM_Frequencies
  52. https://ieeexplore.ieee.org/document/644215
  53. https://www.microwavejournal.com/articles/1388-a-high-efficiency-class-f-power-amplifier-design-technique
  54. https://www.researchgate.net/publication/285182220_Inverse_Class-F
  55. https://ieeexplore.ieee.org/document/9869858
  56. https://www.researchgate.net/publication/368796204_GaN-based_Class-F_Power_Amplifier_for_5G_Applications
  57. https://www.radioeng.cz/fulltexts/2021/21_02_0372_0380.pdf
  58. https://core.ac.uk/download/pdf/36752885.pdf
  59. https://www.researchgate.net/publication/327262915_History_of_Class-F_and_inverse_Class-F_techniques
  60. https://www.highfrequencyelectronics.com/index.php?option=com_content&view=article&id=1259:high-efficiency-doherty-amplifiers-using-class-f-and-inverse-class-f-load-networks-with-a-quarterwave-transmission-line&catid=129&Itemid=189
  61. https://sound-au.com/articles/class-g.htm
  62. https://www.analog.com/en/resources/glossary/class-g.html
  63. https://www.ti.com/lit/pdf/slaa888
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