Chapter 9Linearization and Efficiency Improvements of RF Power Amplifiers
9.1 Introduction
High efficiency and high linearity of power amplifiers [1–85] are of primary importance in wireless communication systems. Wireless communication systems transmit voice, video, and data with high data rates. High efficiency is required for low energy consumption, a longer battery lifetime, and thermal management. Linearity is required for achieving low distortion of the amplified signals. The radio-frequency (RF) power amplifier specifications call for intermodulation (IM) levels of 
dBc. Linearity and efficiency enhancement techniques of RF power amplifiers, which are used in transmitters, are studied in this chapter.
Signals used in modern digital wireless communications systems have a time-varying envelope (amplitude modulation; AM) and time-varying angle (phase modulation; PM)
A nonconstant envelope signal requires linear power amplifiers in the transmitters. The output power in CDMA2000 and WCDMA transmitters may vary in a wide dynamic range of 80 dB. The average output power is usually lower than the peak power by 15–25 dB. The transmitters must be designed for the maximum output power. A high peak-to-average ratio (PAR) drives many power amplifiers into saturation, causing signal ...
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