class A amplifier

class A amplifier

[‚klas ′ā ′am·plə‚fī·ər]
(electronics)
An amplifier in which the grid bias and alternating grid voltages are such that anode current in a specific tube flows at all times.
A transistor amplifier in which each transistor is in its active region for the entire signal cycle.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

amplifier classes

Analog amplifiers are cataloged by how much current flows during each wave cycle. Measured in degrees, 360º means current flows 100% of the time. The more current, the more inefficient and the more heat generated. See amplifier.

Analog



Class A
The amplifier conducts current throughout the entire cycle (360º). The Class A design is the most inefficient and is used in low-power applications as well as in very high-end stereo. Such devices may be as little as 15% efficient, with 85% of the energy wasted as heat.

Class B
The current flows only 180º for half the cycle, or two transistors can be used in a push-pull fashion, each one operating for 180º. More efficient than Class A, it is typically used in low-end products.

Class AB
Combines Class A and B and current flows for 180º to 200º. Class AB designs are the most widely used for audio applications. Class AB amplifiers are typically about 50% efficient.

Class C
Operating for less than half of one wave cycle (100º to 150º), Class C amplifiers are the most efficient, but not used for audio applications because of their excessive distortion.

Class G
A variation of the Class AB design that improves efficiency by switching to different fixed voltages as the signal approaches them.

Class H
An enhancement of the Class G amplifier in which the power supply voltage is modulated and always slightly higher than the input signal.


Current Flowing
The red indicates how much of the time current is flowing through one wave cycle.








Digital



Class D
Class D is a digital-like amplifier that works by turning a transistor fully on or off, but the "D" technically does not stand for digital. See Class D amplifier.

Class T
A variation of the Class D technique from Tripath. Class T modulates the pulses based on the individual characteristics of the output transistors.
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References in periodicals archive ?
In a class A amplifier, the theoretical efficiency is only 50% with actual efficiency in the 20% to 30% range, so output devices tend to be large and robust.
where the conduction angle of a class A amplifier is 2[pi] by definition and the conduction angle of a class AB amplifier is assumed to be 3[pi]/2.
Compared with a class A amplifier, the power capacity of a class C amplifier is decreased by -2.07 dB and the capacity of a class AB amplifier is increased by +0.27 dB.
Many of the amplifiers use a Class A/AB design, claimed to provide better linearity than Class AB or B while improving efficiency compared to a Class A amplifier. Ratings extend to 2,000-W saturated power at 30 MHz and 150-W linear power at 6 GHz.
The model SM0825 40 is a class A amplifier operating from 800 MHz to 2.5 GHz.
Even in high power designs with class A/B outputs, it is common to incorporate class A amplifier stages as drivers or as correction amplifiers in feedforward designs.
A typical value for the third-order intermodulation distortion (IMD) products of a conventional class A amplifier is -35 dBc.
These frequency components are then fed to an ultra linear class A amplifier.
Looking at these drain source currents for the first time, it is somewhat surprising to see how similar the waveforms are, given that the class B amplifier only conducts current during half of the RF input cycle while the class A amplifier conducts during the entire cycle.
For class A amplifiers, the DC supply is constant and the RF amplitudes cannot exceed the biasing voltage and current.
Class AB power amplifiers provide approximately 25 percent efficiency and are more power efficient than class A amplifiers, which only attain approximately five percent efficiency.
A detailed analysis indicates that significant improvements in efficiency while maintaining complete linearity for class A amplifiers can be achieved with step-wise digital control,