8.1 Introduction

Chapter 7 presented the theory of switch mode PAs in much the same way that Chapter 3 presented Class AB modes; the analysis in both cases was loaded with numerous idealizing assumptions, particularly with regard to the device itself. Chapter 4 set out to reinterpret the idealized Class AB analysis in the context of GHz frequency operation. This chapter sets out to perform the same task with switching modes, and as such has the same relationship with Chapter 7 that Chapter 4 has with Chapter 3. Focusing particularly on the Class E mode, we will attempt to reinterpret classical and widely quoted theory, which is based on ideal low frequency models, in the context of GHz frequency applications.

The Class E situation is if anything more extreme than that described in Chapter 4, which referred to Class AB modes. Basically, RF power transistors are not switches at GHz frequencies, even if a finite on resistance is included in the switch model. The assertion that RF power transistors can be considered to operate as switches, sort-of, some-of-the-time, if-you-get-things-right, has to be regarded as questionable at best, and in any case inappropriate, given that accurate nonlinear models are now available for CAD design. The dogmatic faction of the switch-model believers can even go to the extent of jettisoning the detailed nonlinear model that they, or others, use for any other kind of design using the same device, and substituting a simple switch in its place.

Even at this early...