Broadband and Linearity Enhanced Doherty Power Amplifier using Complex-valued Load Modulation

摘要

This paper presents a novel output combining network to enable the extension of the bandwidth of the Doherty power amplifier (DP A) and improve its linearity. This combiner network brings about a complex-valued load modulation to take advantage of the continuous modes of operation for broadening the DP A bandwidth. It is also exploited to devise a nonlinear gain characteristic (AM/AM), which is complementary to the main transistor one and consequently improve the DP A linearity. Accordingly, a 50-W broadband DPA prototype with improved nonlinear gain characteristic is designed to operate over frequency band of 1.5-2.5 GHz while maintaining a drain efficiency in excess of 43 % and small gain variation around 1 dB over the entire 6dB Doherty region. Moreover, the linearizability of the designed DPA was verified under wideband (up to 80 MHz instantaneous bandwidth) and multi-band modulated stimuli using digital predistortion technique.