High–efficiency power amplifiers

This chapter describes amplifiers or amplification output stages that are capable of delivering high-output power levels. Since power amplifier stages may deliver high output power to low-impedance loads, they are significantly different from the low-power small signal amplifiers. Class-A operation is the only configuration that will yield low distortion signals. Class-B and class-AB power amplifiers assure signal continuity by making use of arrangements of two transistors that allow each transistor to share portions of the input signal conduction angle. The high-efficiency amplifiers based on this approach are usually classified as class-D, class-E and class-F, being also referred to as switching amplifiers or digital amplifiers. To compare the design of power amplifiers, different figures of merit or parameters can be utilized. Large input signal to power amplifiers causes the amplifier to yield distorted output signals. In fact, in large-signal operation, the signals overtake the limits of the transistor forward-active region, causing distortion at the output.
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