Hybrid Analog/Digital Continuous Class B/J Mode for Broadband Doherty Power Amplifiers

Abstract

In this paper, a new digitally driven two input continuous mode Doherty power amplifier (DPA) architecture is proposed along with an analytical-based generic output combiner network design methodology. The load combiner provides the designer a choice to meet the optimum performance for any arbitrary back-off as well as for saturation. The PA's performance is further optimized with digital input splitting. To verify the proposed theory, a 20-W symmetrical continuous mode DPA is designed using 10-W GaN HEMTs. The proposed amplifier shows a drain efficiency between 56.0% and 75.4% at 41.4-44.6 dBm saturation power and between 45% and 56.5% at 35.7-38.5 dBm output power corresponding to 6-dB back-off. This performance is achieved over the band from 1.25 to 2.3 GHz that corresponds to 59.15% fractional bandwidth. The proposed hybrid analog/digital continuous mode DPA prototype is implemented using field-programmable gate array (FPGA)/DSP platform and qualifies the spectral mask when excited by a modulated long term evolution signal along with digital predistortion.

Keywords

• Broadband DPA
• digital phase compensation
• continuous mode
• high efficiency
• back-off