Doherty power amplifier using a compact load network for bandwidth extension

Abstract

This paper presents a Doherty power amplifier (DPA) with a compact load network for an extended bandwidth compared to the conventional DPA. The compact load network takes less area since it has just one load matching network after the quarter-wave transmission line and no offset-lines. For the verification, both conventional and compact DPA's are designed and built using GaN HEMT for the band from 650 to 800 MHz. They were evaluated using the down-link 16-QAM FDD LTE signal that has a PAPR of 9.96 dB and a signal bandwidth of 5 MHz. At an average output power of 34 dBm, which is approximately 9 dB back-off from the 1 dB compression point, the proposed compact DPA exhibited a power-added efficiency (PAE) level of more than 40% and an adjacent channel leakage power ratio (ACLR) level of lower than -25 dBc over the frequency band of from 650 to 800 MHz, while the conventional DPA showed a PAE level of more than 26.6% and an ACLR level lower than -23 dBc. In addition, the proposed compact DPA has a reduced circuit size by 40.9% compared to the conventional one.