Introduction

PA linearization has become a subject in its own right in recent years, and has seen a large investment of research and development funding in both the industrial and academic sectors. It has been the subject of dedicated books [1 3] and on the conference circuit has grown from one or two papers into multiple sessions, and even entire symposiums. It has also been a very active area for venture capital spending. Every few months, it seems, a new start-up company lets out a press release proclaiming their totally new, disruptive linearized PA technique which will revolutionize the industry; another heavily patented area. This chapter is presented as an update and an overview of PA linearization. More focused treatment has been restricted to certain topics in digital predistortion and feedforward, these being the techniques that are in current use and still undergoing intensive development for wireless communications applications. Other techniques such as various kinds of feedback will be described but not fully analyzed, since they have found less use in modern wireless PA applications.

Chapter 13 described techniques which improve efficiency, without attempting to quantify the impact on linearity or RF power output. Such techniques are of paramount importance in mobile systems, where battery lifetime and thermal management are critical. There are other PA applications where efficiency becomes an important, but secondary consideration, in comparison to linearity. Such applications would typically be single or multichannel basestation transmitters in ground or satellite communications systems. Commercial competition, in particular between system operators...