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 3: Class-F Power Amplifiers
Highly efficient operation of the power amplifier can be obtained by applying biharmonic or polyharmonic modes when an additional single-resonant or multi-resonant circuit tuned to the odd harmonics of the fundamental frequency is added into the load network. An infinite number of odd-harmonic resonators results in an idealized Class-F mode with a square voltage waveform and a half-sinusoidal current waveform at the device output terminal. In Class-F power amplifiers analyzed in frequency domain, the fundamental and harmonic load impedances are optimized by short-circuit termination and open-circuit peaking to control the voltage and current waveforms at the device output to obtain maximum efficiency. In this chapter, different Class-F techniques, using lumped and transmission-line elements including a quarter-wave transmission line, are analyzed. The effect of the saturation resistance and parasitic shunt capacitance is demonstrated. The design examples and practical RF and microwave Class-F power amplifiers are described and discussed.
3.1 Biharmonic Operation Mode
In a Class-B operation mode, the maximum theoretical anode (collector or drain) efficiency achieves only 78.5% characterizing by the sinusoidal anode voltage waveform and half-sinusoidal current waveform. In real practical power-amplifier design, especially at high frequencies and low supply voltage, efficiency significantly degrades. Therefore, some design, solutions contributing to efficiency improvement were published a long time ago with regard to the vacuum-tube power amplifiers and were based on the harmonic tuning at the anode of the active device. To understand this basic approach, let us evaluate a contribution of each harmonic component to ideal half-sinusoidal current waveform and square...
Copyright Elsevier Inc. 2007 under license agreement with Books24x7
