A Mixed-Technology Asymmetrically Biased Extended and Reconfigurable Doherty Amplifier With Improved Power Utilization Factor

Abstract

In this paper, we present a mixed-technology extended Doherty amplifier using asymmetrical voltage biasing with an LDMOS main device and a GaN auxiliary device to improve the power utilization factor of the amplifier. Moreover, in contrast to previous work, the amplifier can achieve reconfigurable back-off power ranges and an extended bandwidth without using a mixed-signal setup. The analysis also highlights the relationship between power utilization and the range of the reconfigurable back-off power level. Finally, we demonstrate that the proposed amplifier can be optimally configured for a given modulated signal to obtain the highest average efficiency. A 180-W mixed-technology prototype Doherty amplifier measured peak and back-off efficiencies greater than 50% when configured for 6, 8, and 10 dB of back-off power level at 790, 870, and 960 MHz under continuous-wave stimulus. The amplifier is highly linearizable when driven with 20-MHz long-term evolution and WCDMA signals, achieving adjacent channel power ratio of better than -50 dBc after digital pre-distortion linearization.