A 38GHz Power-Combined Doherty PA Based on an Extended Rat-Race Coupler Achieving 27.5dBm Saturated Power and 15.0% Efficiency at 6dB Back-Off.

Phased arrays serve as the foundational technology for mmWave communications to combat the path loss and improve the energy efficiency. Although phased arrays are ubiquitous at mmWave, it is still desirable to realize high output power per antenna for user equipment (UE) and small cells due to their array size constraints. Recent advances in mmWave silicon power amplifier (PA) research have led to significant performance improvement for low-and medium-power PAs $(\lt 23 \mathrm{dBm})$. However, design of high-power yet high-efficiency PAs still remains challenging.This work aims to demonstrate Watt-level PA output power $(\gt 27 \mathrm{dBm})$ with back-off efficiency enhancement. Back-off efficiency enhancement is particularly attractive for UE and small-cell PAs to extend their battery lives under spectral-efficient modulations. Among various efficiency enhancement techniques, Doherty architecture can potentially enable wider bandwidths due to its lower digital computation overhead. Therefore, our design goal is to develop a multi-functional PA output network to achieve (1) Doherty load modulation, (2) multi-way power combining, and (3) differential to single-ended conversion simultaneously, as shown in Fig. 1.