Power Amplifer

Class A
Class A power amplifiers are designed using only one switching transistor. The transistor type (BJT, IGBT, FET) depends on the intended end use application. These are linear amplifiers with high gain and 360° conduction angle.

Class B
Class B power amplifiers attempt to solve the heating problem in Class A amplifiers by using two complementary transistors to amplify the entire waveform. The conduction angle for each transistor is 180°, i.e., both remain in the ON state for half the duration of the input signal.

Class AB
This configuration is a blend of Class A and Class B power amplifiers. It solves the problem of reduced efficiency due to overheating. It simultaneously reduces the crossover distortion present in Class B power amplifiers through the use of a combination of diodes and resistors to provide a bias voltage.

Class C
The conduction angle in Class C power amplifiers is less than 90°. Consequently, these amplifiers are unsuitable for audio amplification because a smaller conduction angle leads to more distortion. Class C amplifiers have a tuned load that enhances one frequency while suppressing others.

Class D
Class D amplifiers need much smaller power transformers than other amplifiers because PWM permits amplification at considerably higher frequencies. They are ideal for applications that require large power amplification in a small package, such as in power amplifiers for wireless protocols.

Class F
Class F amplifiers use a set of harmonic resonators (high-Q parallel LC circuits) to boost output power delivered to a load and provide high efficiency. The series of harmonic resonator circuits allows the input modulating signal to generate harmonic components at multiples of some fundamental frequency.

Class G
Class G amplifiers automatically shift between numerous power supply rails at different voltages as the input signal is varied. Class H amplifiers are also a variation of Class G amplifiers, except they use an infinitely variable analog supply rail. The use of continual switching decreases power losses in the transistor’s conduction channel.

Class I
Class I amplifiers have two sets of complementary output switching circuits stacked in a parallel push-pull configuration, similar to a bridge circuit. The basic concept is the same as in a Class B amplifier: one device is active during the positive half cycle while the other is active during the negative half cycle.

Class S
Class S power amplifiers are similar to Class D power amplifiers. These digital pulses are then amplified to the desired power output level. As this signal is passed to the output, a high-Q bandpass filter is then used for demodulation at the desired frequency.