An Overview of Envelope Tracking PAs and Hybrid Supply Modulators in CMOS Technologies
Envelope Tracking has to-date been the most popular technique in wireless handsets for boosting RF power amplifier efficiency at power backoff levels. ET systems have high integration capability within cellular handset devices, and therefore the demand for ET integrated circuits (ICs) to support the smart-phone market continues to rapidly grow as the wireless communication market moves into the fifth-generation (5G) era. This talk reviews trends, architectures, and recent developments in CMOS-based supply modulators (SM) used for envelope-tracking power amplifiers (ET-PAs). This review details the most commonly used hybrid supply modulator (HSM), and discusses its performance requirements and design challenges. The importance of efficiency, speed, linearity, and output power in HSM design is delineated and different methods that focus on maximizing these performance parameters are presented. Finally, the design challenges of envelope tracking systems are discussed, and an overview of device technologies for SM and ET-PA implementations is given.