A 28-GHz 256-QAM Power Amplifier with Weakly-Coupled Transformers in 65-nm CMOS

This paper presents a 28-GHz three-stage pseudodifferential neutralized power amplifier (PA) for 5G applications. A fully-coupled transformer is chosen as the output matching network to reduce loss and improve efficiency, while weakly-coupled transformers are adopted as the input and inter-stage matching networks to extend bandwidth. An optimization method is proposed to ensure power performance while maintaining bandwidth. Implemented in 65-nm CMOS technology at 1-V supply, the prototype delivers a saturated output power of 12.7 dBm with a peak PAE of 29.5%. It offers a small signal gain of 23.7 dB with 3-dB bandwidth from 25.9 GHz to 33.1 GHz. The chip occupies a core area of 0.82×0.24 mm
²
.