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RF and Microwave Transmitter Design by Andrei Grebennikov

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12

Linearization and Efficiency Enhancement Techniques

In modern wireless communication systems, it is very important to realize simultaneously high-efficiency and linear operation of the power amplifiers. This chapter describes a variety of techniques and approaches that can improve the power amplifier performance. To increase efficiency over power backoff range, the Doherty, outphasing, and envelope-tracking power amplifier architectures, as well as switched multipath power amplifier configurations are discussed and analyzed. There are several linearization techniques that provide linearization of both entire transmitter system and individual power amplifier. Feedforward, cross cancellation, or reflect forward linearization techniques are available technologies for satellite and cellular base station applications with achieving very high linearity levels. The practical realization of these techniques is quite complicated and very sensitive to both the feedback loop imbalance and the parameters of its individual components. Analog predistortion linearization technique is the simplest form of power amplifier linearization and can be used for handset application, although significant linearity improvement is difficult to realize. Different types of the feedback linearization approaches together with digital linearization techniques are potentially attractive to be used in handset or base station transmitters. The choice of a proper high-efficiency approach or linearity correction ...

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