High-Efficiency Doherty Power Amplifiers: Historical Aspect and Modern Trends

In modern wireless communication systems, it is very important to realize simultaneously high-efficiency and linear operation of power amplifiers. This paper-review describes the historical aspect of the Doherty approach to the power amplifier design introduced in 1936 and modern trends in Doherty amplifier design techniques using multistage and asymmetric multi-way architectures. To increase efficiency over the power backoff range, the switch-mode Class E, conventional Class F, or inverse Class F operation mode by controlling the second and third harmonics can be used in the load network. The Doherty amplifier with a series connected load, inverted and dual-mode Doherty architectures are also described and discussed. Finally, examples of the lumped Doherty amplifier implemented in monolithic microwave integrated circuits and broadband capability of the two-stage Doherty amplifier are given.