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amplifier class

Amplifiers are developed and built for completely different applications, as small signal amplifiers, preamplifiers, RF amplifiers, power amplifiers or push-pull amplifiers. In order to fulfill the different applications optimally, the circuit concepts must be adapted to the corresponding requirements.

To provide the user with comparison options, the various amplifier concepts have been divided into different amplifier classes, which are identified by letters. In addition to the generally comparable classes A, B, AB, C, D, E, F and S, there are also manufacturer-specific classes, such as the T class.

Amplifier classes A, B and AB are for power amplifiers characterized by linear behavior. The other classes are for RF amplifiers, modulators and preamplifiers and have nonlinear behavior.

ClassA: In power amplifiers with A operation, the operating point is selected so that linear amplification occurs over the entire input and output voltage range. Class A amplifiers are characterized by their low distortion in the zero-crossing range and have therefore also gained acceptance in terms of sound quality. It is a single-ended output stage with a relatively high linearity. The efficiency is low, theoretically at 50%, practically far below. Therefore, power amplifiers of the A class become relatively warm when operated in power mode.

Amplifier classes

Amplifier classes

B class: Amplifiers in B mode are push-pull amplifiers with two active components in push-pull operation. The operating point is selected so that linear amplification takes place in one of the two active components at a time over the entire input and output voltage range, but the transition of the characteristic curves is characterized by a high degree of nonlinearity. The achievable efficiency is 75% and above, i.e. much higher than that of the A class, but the linearity is worse.

AB class: Amplifiers with AB operation are driven in single-ended mode, like the A amplifier, but operate with balanced voltage supply. The transistors arranged in complementary circuitrydirectly drive the loudspeaker in the emitter circuits. The non-linearity of the B class is eliminated by diodes in the base circuit, without the AB class having the inefficiency of the A class. The AB circuit features excellent linearity and efficiency well above 50% and is the most commonly used power amplifier design.

C-class: These amplifier circuits operate with an active component. They are used in RF technology, primarily as RF power amplifiers in transmitters, but are not suitable for all modulation methods. C amplifiers have high nonlinearities and high efficiency and are used for driving antennas.

D class: Class D amplifiers are switching amplifiers for clocked operation. They operate in push-pull mode with two active devices and function as switching amplifiers with extremely high efficiency and low losses. D amplifiers are also used as clocked amplifiers with pulse width modulation in the audio sector. Here, the analog audio signals are converted into digital signals in an A/D converter; these are pulse-width modulated, amplified and converted back into analog signals in a downstream D/A converter.

E-class: E-class amplifiers are designed to amplify square wave signals and pulses, not sine wave signals. The output load is a tuned circuit, resulting in an attenuated sinusoidal signal. The simplest form of an E-class amplifier consists of a single transistor that acts as a switch.

F-class: In the F-circuit, the electronic component is operated in the non-linear characteristic part, which results in the generation of harmonics. It is a tunable power amplifier with a tunable resonant circuit. Tuning is performed on the carrier frequency and on one or more harmonics.

G-class: The G-class is a special version of the AB amplifier that operates with a higher amplitude excitation. For this purpose, the G class either uses two busbars and a switching technique that becomes active when a higher level control is applied, or it works with two output stages and two different supply voltages with which they are supplied. In this constellation, the input amplitude determines the signal path.

H-class: The H-class goes one step further and modulates the supply voltage with the input signal. Thus, a high input signal causes a high supply voltage.

S-class: The S-circuit corresponds to the D-class with the difference that it is designed for lower frequency signals. It is a circuit in which the active element is used for amplification and amplitude modulation.

Englisch: amplifier class
Updated at: 04.03.2021
#Words: 701
Links: signal, power (P), indium (In), order, user
Translations: DE

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