Harnessing Harmonics in Doherty Power Amplifiers [Application Notes]

Abstract

Doherty power amplifiers (DPAs) [1] are widely used as basestation PAs in modern wireless communication systems and have been well-reviewed [2]. Due to its mechanism of load modulation, the DPA exhibits an additional efficiency peak at a certain output power back-off (OBO). This makes the DPA highly desirable for amplifying modulated signals with high peak-to-average power ratios (PAPRs). However, there still are limitations that restrict its use in modern and future wireless communication systems. To meet the insatiable demand for higher data rates, modulated signal formats require an everhigher PAPR (>6 dB). This, in turn, means that the DPA needs to operate at a greater OBO >6 dB). Hence, the design of extended back-off DPAs is of great interest to engineers. Broadband operation is also required, but, unfortunately, the DPA?s efficiency at back-off decreases with an increase in bandwidth. Therefore, a technique to achieve high efficiency at back-off, not at the expense of the bandwidth, is urgently needed.