Chapter 9Baseband Digital Predistortion

9.1 The Predistortion Concept

The ultimate aim of studying power amplifier (PA) distortions is to design appropriate predistorters that will compensate for these distortions and ensure linear amplification of the signal to be transmitted. In Chapter 3, the similarities between behavioral modeling and digital predistortion (DPD) were briefly introduced. Various mathematical formulations that can be used to implement behavioral models as well as digital predistorters were thoroughly discussed in Chapters 47. Chapter 8 exposed the common steps of the behavioral modeling and DPD processes with a focus on the identification techniques employed for the synthesis of the model or predistorter function. In this chapter, the specificities of DPD are addressed. Although the analysis is carried out in this chapter for the case of a PA, the concepts and results still hold in the case where the transmitter's analog front end is part of the device under test (DUT) to be linearized.

Conceptually, predistortion consists in implementing a nonlinear function upstream of the PA complementary to that of the amplifier to be linearized. Accordingly, the cascade made of the predistorter and the PA will operate as a linear amplification system as illustrated in the simplified block diagram of Figure 9.1. This figure also depicts sample amplitude modulation to amplitude modulation (AM/AM) and amplitude modulation to phase modulation (AM/PM) characteristics of ...

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