RF Power Amplifiers
In this comprehensive reference, the author presents a full account of RF amplifiers and shows that understanding large-signal RF circuits is simply a matter of understanding the basic principles and their applications.
TABLE OF CONTENTS RF Power Amplifiers
Chapter 5: Class F Amplifiers
Several different power amplifier topologies that provide high efficiency are known as Class F amplifiers. Although these topologies may appear distinct from one another, they all use a multiple-resonator output filter. This filter controls the harmonic content of the collector voltage and/or current, by shaping their waveforms to reduce the power dissipated on the active device. This, in turn, increases the collector efficiency.
The literature uses many different names to describe this concept: high-efficiency Class C, Class C using harmonic injection, optimum efficiency Class B, optimally loaded Class B, Class CD, single-ended Class D, multiple-resonator Class C, biharmonic or polyharmonic Class C, and even Class E. Recent literature tends to designate all circuits using a multiple-resonator output filter as Class F amplifiers. Further classification of Class F circuits is provided in Reference [1] and will be used in this chapter. Class F circuits are divided into three categories: Class F1, F2, and F3.
5.1 Class F1 Power Amplifiers
The output filter of a Class F1 amplifier resonates on both the operating frequency and one of its harmonics, usually the second or third. The corresponding circuits are also known as second-harmonic peaking Class F PA, and third-harmonic peaking Class F PA, respectively.
The basic circuit of a Class F1 amplifier employing the third harmonic is shown in Figure 5-1 [1 7]. Figure 5-2 presents the characteristic waveforms of the circuit. This circuit is similar to that of a single-ended Class B or Class C amplifier, except for the addition of a third-harmonic parallel...
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