A Millimeter-Wave Watt-Level Doherty Power Amplifier in Silicon
Xiaohan Zhang, Sensen Li, Taiyun Chi
Abstract
This article presents a millimeter-wave (mmWave) power-combined Doherty power amplifier (PA) topology. To reach watt-level output power and simultaneously enhance back-off efficiency, we propose a multifunctional PA network based on an extended rat-race coupler, which enables the following: 1) parallel Doherty load modulation; 2) multiway series power combining; and 3) differential to single-ended conversion. As proof of concept, a 38-GHz PA prototype is implemented in the GlobalFoundries 45-nm CMOS SOI process. It demonstrates 27.5-dBm saturated power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm{ SAT}}$ </tex-math></inline-formula> ), 26.9-dBm output 1-dB compression point ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{1\,\text {dB}}$ </tex-math></inline-formula> ), and 15.0% power-added efficiency (PAE) at 6-dB back-off. Among recently reported 30–50-GHz silicon-based high-power PAs with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$>$ </tex-math></inline-formula> 23-dBm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm{ SAT}}$ </tex-math></inline-formula> , our design demonstrates the highest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{1\,\text {dB}}$ </tex-math></inline-formula> and PAE at 6-dB back-off. Tested under 200-MSym/s 64-QAM modulation, the PA achieves 20.0-dBm average output power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm{ avg}}$ </tex-math></inline-formula> ) and 12.2% average efficiency (PAEavg).