Generalized Expression and Design Method of Modified Load Networks for Doherty Power Amplifier With Extended Back-Off Range
Yifei Chen, Woojin Choi, Jaekyung Shin, Hyeongjin Jeon, Sooncheol Bae, Young Chan Choi, Seungmin Woo, Young Yun Woo, Hansik Oh, Kang‐Yoon Lee, Keum Cheol Hwang, Youngoo Yang
Abstract
This paper presents a generalized expression of the modified load networks (MLNs) for Doherty power amplifiers (DPAs) with an extended output power back-off (OBO) range. Based on the analysis using this new expression, a new circuit structure generally applicable to any combination of the multiple MLNs is proposed. The load network has a simple structure including impedance matching circuits and offset lines for the carrier and peaking amplifiers. A design procedure for the proposed load network is presented. A DPA using any optimized combination of the multiple MLNs can be easily designed using the proposed load network. For verification, a GaN-HEMT symmetrical DPA based on a combination of the virtual open-stub (VOS) and out-phased current combining (OCC) methods was designed and implemented for the frequency band of 3.4 - 3.7 GHz. The reversed uneven power splitting method is adopted in the design for higher power gain. Using the 5G New Radio (NR) signal with a peak-to average power ratio (PAPR) of 7.9 dB and a signal bandwidth of 100 MHz, the proposed DPA exhibited DE of 55.3 - 60.9% with a power gain of 11.9 - 12.7 dB at an average output power of 33.7 dBm. An adjacent channel leakage power ratio (ACLR) of -42.6 - -44.8 dBc was achieved at the average power level by using a digital predistortion (DPD) technique across the band.