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

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 mm2 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. [ABSTRACT FROM AUTHOR]