A 28GHz Packaged Chireix Transmitter with Direct on-Antenna Outphasing Load Modulation Achieving 56%/38% PA Efficiency at Peak/6dB Back-Off Output Power

This paper presents a packaged 28GHz Chireix outphasing transmitter (TX) for power amplifier (PA) efficiency enhancement at peak and back-off output power (PBO). It utilizes a high-efficiency dual-feed loop antenna (DLA)-based non-isolating power combiner to realize direct on-antenna power combining and more importantly, outphasing active load modulation. The proposed Chireix TX contains two phase-shifted sub-TXs simultaneously driving a DLA on package. The TX chips are implemented in a 45nm CMOS SOI process and integrated with the DLA by flip-chip packaging. The measurements demonstrate a 56% PA drain efficiency (η_D) at saturated power (Psat), with 38% η_Dat 6dB PBO, achieving 1.36× efficiency enhancement over ideal Class-B operation. The high efficiency of this Chireix TX enables up to 34%/10.5dBm PA average efficiency/output power (η_ave/P_ave) while amplifying 15Gb/s 64-QAM signal at 28GHz with EVM/ACLR better than -27.5dBc/-28dBc in a wireless radiation testing environment.