Broadband Highly Efficient Doherty Power Amplifiers

Modern wireless communication systems with large bandwidth and high peak-to-average power ratios (PAPRs) have been and will continue to be in high demand. This puts a strain on the transmitter, which has to operate with its average power in the output back-off (OBO) region. The Doherty power amplifier (Doherty PA) was invented in 1936 as an alternative to the highly inefficient linear amplifiers used in radio transmitters. The Doherty PA has recently undergone a renaissance, becoming the PA architecture of choice for mobile radio base stations. The additional efficiency peak at the OBO point makes it ideal for high PAPR signals. However, the main drawback of conventional Doherty PAs is its narrow bandwidth, which significantly limits its applicability. Recently, broadband Doherty PAs have been realized using a technique called "post-matching" and have attracted much attention. In this paper, the operating principles of conventional and broadband Doherty PAs are reviewed, followed by an analysis of recently reported prototypes, current technical challenges, and application in 5G wireless communication systems. As a comparison, process technologies for the implementation of Doherty PAs are also surveyed.