Doherty Power Amplifiers Move to mmWave.

Doherty power amplifiers (PA) are widely used below 6 GHz to improve power-added efficiency (PAE) for communications applications. Although the benefits of the Doherty architecture are compelling, the challenges of designing Doherty PAs increase as the frequency of operation moves toward mmWave. LDMOS, which is commonly used in discrete form below 6 GHz, has limited performance and more integrated approaches are needed to minimize parasitic inductances and capacitances. GaN technology offers significant performance advantages for realizing RF/microwave PAs. More recently, short gate length GaN on SiC MMIC processes have become commercially available, offering the possibility of designing high efficiency Doherty PAs at mmWave frequencies. This article will describe the design of a Doherty PA MMIC for the 5G frequency band at 28 GHz. First-pass design success was achieved using an asymmetric topology fabricated on the commercial 0.15 µm G28v5 GaN on SiC foundry process from Wolfspeed. The MMIC was assembled in a cost-effective, compact 4 mm x 4 mm QFN package. Details of the design, simulation, layout and packaging will be discussed. [ABSTRACT FROM AUTHOR]