I. Introduction
Radio-Frequency (RF) power amplifiers are important in numerous applications, including RF communications, medical imaging, industrial heating and processing, and dc-dc power conversion among many others. Power amplifiers (PAs) are often required to provide linear amplification, which encompasses the ability to dynamically control the RF output power over a wide range. This becomes particularly challenging when wide-bandwidth control of the output is required. It is also often desired to maintain high efficiency across a wide range of output power levels, such that high average efficiency can be achieved for highly modulated output waveforms. Simultaneously achieving both of these requirements—wide-bandwidth linear amplification and high average efficiency—has been a longstanding challenge, and is the goal of this paper.