A Broadband Switched-Transformer Digital Power Amplifier for Deep Back-Off Efficiency Enhancement

• Published in: IEEE journal of solid-state circuits 2020-11, Vol.55 (11), p.2997-3008
• Main Authors: Yin, Yun, Li, Tong, Xiong, Liang, Li, Yicheng, Min, Hao, Yan, Na, Xu, Hongtao
• Format: Article
• Language: English
• Subjects: Broadband; CMOS; Coils; deep back-off; digital power amplifier (DPA); Doherty; Dynamic loads; efficiency enhancement; Impedance; Local area networks; Modulation; Power amplifiers; Power combiners; Power generation; switched transformer; Switches; Switching circuits; Transformers; Wireless networks
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2020.3005798

This article presents a switched-transformer-based polar Doherty digital power amplifier (DPA) for deep back-off efficiency enhancement. A single-transformer-footprint parallel-combining transformer (PCT) power combiner is introduced for 1.3-3.5-GHz wide frequency coverage, dynamic load modulation at 0-/6-/12-/18-dB power back-off (PBO) levels, and an ultra-compact die size. Implemented in 40-nm CMOS, the DPA is powered by a 1.1-V supply and only occupies 0.7 \times 1.15 mm 2 chip area. It achieves 21.4-dBm peak power with the power added efficiencies (PAEs) of 31.3%, 27.7%, 16.6%, and 7.7% for 0-/6-/12-/18-dB PBOs at 1.5 GHz. With 20-MHz 64QAM long term evolution (LTE) signal, the DPA achieves {P}_{{\text {avg}}} of 15.2 dBm and the average PAE of 25.3% with −32.5-dB error vector magnitude (EVM) at 1.5 GHz. Moreover, for 20-MHz 64 QAM WLAN signal, {P}_{{\text {avg}}} of 14.7 dBm with the average PAE of 20.1% is obtained with − 25-dB EVM at 2.4 GHz.