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 7: Class E with Quarter-wave Transmission Line
This chapter presents the results of exact time-domain analysis of the switched-mode tuned Class-E power amplifiers with a quarter-wave transmission line. The load-network parameters are derived analytically. The ideal collector voltage and current waveforms demonstrate a possibility of 100% efficiency without overlapping each other. The load network implementation including output-matching circuit at RF and microwave frequencies using lumped and transmission-line elements is considered with accurate derivation of the matching-circuit parameters. The switched-mode Class-E power amplifiers with a quarter-wave transmission line offer a new challenge for RF and microwave power amplification providing the high-efficiency and harmonic-suppression operation conditions.
7.1 Load Network with Parallel Quarter-wave Line
The ideal Class-F load network with a quarter-wave transmission line and a series L 0C filter tuned to the fundamental frequency can provide a collector efficiency of 100% when the open-circuit conditions for odd-harmonic components and short-circuit conditions for even-harmonic components are realized. However, in practice, the idealized collector rectangular voltage and half-sinusoidal current waveforms corresponding to a Class-F operation mode provided by using a quarter-wave transmission line in the load network can be realized at sufficiently low frequencies when an effect of the device output capacitance shown in Figure 7-1 is negligibly small. Generally, the effect of the device output capacitance contributes to a finite switching time resulting in time periods when the collector voltage and collector current exist at the same time. As a result, such a load network with the quarter-wave transmission line and shunt capacitance cannot provide the switched-mode operation...
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