Switchmode RF Power Amplifiers
Switching mode RF amplifiers have become a hot area of RF/wireless design. This book explores both the theory behind switching mode RF amplifiers and design techniques for them.
TABLE OF CONTENTS Switchmode RF Power Amplifiers
Chapter 5: Class E with Shunt Capacitance
The switched-mode Class-E tuned power amplifiers with a shunt capacitance have found widespread application due to their design simplicity and high efficiency operation. Their load network configuration consists of the shunt capacitance, series inductance, and series filter tuned to the fundamental frequency to provide a high level of harmonic suppression. In the Class-E power amplifier, the transistor operates as an on-to-off switch and the shapes of the current and voltage waveforms provide a condition when the high current and the high voltage do not overlap simultaneously that minimizes the power dissipation and maximizes the power-amplifier efficiency. In this chapter, the historical aspect and modern trends of a Class-E power-amplifier design are presented. Different circuit configurations and load network techniques using the push-pull mode, lumped, and transmission-line elements are analyzed. The effect of the device saturation resistance, finite switching time, and nonlinear shunt capacitance is described. The practical RF and microwave Class-E power amplifiers and their applications are given and discussed.
5.1 Effect of Detuned Resonant Circuit
Using resonant circuits tuned to the odd or even harmonics of the fundamental frequency in the load network by realizing biharmonic or polyharmonic operation modes of the vacuum-tube power amplifiers is very effective to increase their operating efficiency. This implies ideally the in-phase or out-of-phase harmonic conditions when symmetrical flattened voltage or current waveforms can be formed. However, as it turned out, this is not the only way to improve the power-amplifier efficiency. Fig. 5.1 shows the circuit schematic of the vacuum-tube power amplifier...
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