Leveraging Programmable Capacitor Arrays for Frequency-Tunable Digital Power Amplifiers

This article presents a digitally frequency-tunable switched-capacitor power amplifier (SCPA) in 65-nm CMOS. The operable frequency range spans from 1.4 to 2.5 GHz. The center frequency is tuned by a programmable capacitor array, widely available from both monolithic microwave integrated circuit (MMIC) and MEMS manufacturers. A prototype is able to achieve a peak output power of 21.7 dBm with a peak system efficiency (SE) of 38.8%, while achieving 58.8% fractional bandwidth. When transmitting a 20-MHz, 64-quadrature amplitude modulation (QAM) long-term evolution (LTE) signal, it outputs 14.1 dBm at 15.7% SE with a measured adjacent channel leakage ratio (ACLR) <; -30 dBc and error vector magnitude (EVM) of <; 3.9% rms, without the use of digital predistortion (DPD).