An Eight-core Class-G Switched-capacitor Power Amplifier with Eight Power Backoff Efficiency Peaks

Abstract

An eight-core class-G polar switched-capacitor power amplifier (SCPA) is described that uses an eight-way digitally-scalable transformer (DST) and a new pseudo-differential class-G switch. Employing both supply and load modulation, eight seamless efficiency peaks are realized at 0 dB, 2.5, 6, 8.5, 12, 14.5, 18 and 24 dB power backoff levels by minimizing the dynamic switching loss in the capacitor array. A prototype chip was designed and fabricated in a 65nm CMOS process. It achieves peak output power and drain efficiency (DE) values of 27.2 dBm and 35.5%, respectively, at a carrier frequency of 2.42 GHz. Compared to a normalized class-B power amplifier, the measured DE is increased by $\sim 3.3\ \mathrm{X}$. which corresponds to a 70% power saving. For a single-carrier 64 QAM signal with a 1 MHz bandwidth, the measured average output power and DE are 20.0 dBm and 23.1%, respectively, with an error vector magnitude (EVM) of −28.6 dB.