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Chapter 2 Class E Power Amplifiers and Its Linearization 2.1 Introduction

To improve the performance of wireless systems, Amplifiers operated in the Radio Frequency (RF) band are used both in the wireless transmitter and receiver. Power amplifiers (PAs) are used in the transmitter to enable power amplification of baseband signals. The selection of PAs for the transmitter is based on the efficiency, Device Utilization Factor (DUF) and linearity of the amplifier. The DUF is very low for Class E PA than the other PAs. To achieve high efficiency, Class E power amplifiers are preferred. Class E PAs operate with power losses lesser than class B or class C amplifiers. They can be constructed with Silicon or Gallium Arsenide semiconductors in CMOS technology. Class E PAs can be designed for narrowband operations and give maximum output power for 50% duty cycle. High power amplifiers in the base stations and the repeaters for wireless systems need extremely high linearity. In Class E PAs, the effect of components and frequency variations are small since the MOSFET device is operated in switching mode. But the drawback of Class E PAs is the nonlinearity of the amplifier. This drawback can be improved by linearization techniques like analog Predistortion, digital Predistortion, feed forward Predistortion etc. In this thesis, an attempt is made to linearize the PAs using Analog Predistortion method.