A Generic Theory for Design of Efficient Three-Stage Doherty Power Amplifiers

• Published in: IEEE transactions on microwave theory and techniques Vol. 70; no. 2; pp. 1242 - 1253
• Main Authors: Zhou, Han, Perez-Cisneros, Jose-Ramon, Hesami, Sara, Buisman, Koen, Fager, Christian
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.02.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Combiner synthesis; Complexity theory; Delays; Design; Doherty power amplifiers; Doherty power amplifiers (PAs); Efficiency; energy efficiency; Gallium nitride; gallium nitride (GaN); Gallium nitrides; high peak-to-average power ratio (PAPR); Impedance; Peak to average power ratio; Power amplifiers; Power generation; Semiconductor devices; three-stage symmetrical devices; Transistors
• ISSN: 0018-9480; 1557-9670; 1557-9670
• DOI: 10.1109/TMTT.2021.3126885

An analytical load-pull-based design methodology for three-stage Doherty power amplifiers (PAs) is presented and demonstrated. A compact output combiner network, together with the input phase delays, is derived directly from transistor load-pull data and the design requirements. The technique opens up a new design space for three-stage Doherty PAs with reconfigurable high-efficiency power back-off levels. The method is designed to enable high transistor power utilization by maintaining full voltage and current swings of the main and auxiliary amplifier cells. Therefore, a wide efficiency enhancement range can be achieved also with symmetrical devices. As a proof of concept, a 2.14-GHz 30-W three-stage Doherty PA with identical gallium nitride (GaN) HEMT active devices is designed, fabricated, and characterized. The prototype PA is able to linearly reproduce 20-MHz long-term evolution signals with 8.5- and 11.5-dB peak-to-average power-ratio (PAPR), providing average efficiencies of 56.6% and 46.8% at an average output power level of 36.8 and 33.8 dBm, respectively. Moreover, an average efficiency as high as 54.5% and an average output power of 36.3 dBm have been measured at an adjacent power leakage ratio of −45.7 dBc for a 100-MHz signal with 8.5 dB of PAPR, after applying digital predistortion linearization.