4.1: Introduction

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This chapter considers amplifiers that are designed to produce large RF powers and achieve high efficiency. The design of such amplifiers is more complicated than the design of small signal amplifiers, which can be designed using linear techniques. It is now necessary to use nonlinear simulation tools and laboratory optimization to develop designs that achieve high efficiency with acceptable distortion [1]. The design of power amplifiers involves the trade-off of distortion and amplifier efficiency. Before beginning this chapter the reader should be familiar with the metrics for nonlinear distortion described in Section 4.5 of [2].

Transistors used in microwave amplifiers are large, as can be seen in Figure 4.2.1. This transistor is targeted for use in WCDMA amplifiers operating between \(2.11\) and \(2.17\text{ GHz}\) with an output power of \(140\text{ W}\) at \(1\text{ dB}\) gain compression. The transistor includes input and output matching networks in the package. This provision by the transistor vendor reduces the complexity of amplifier design.