A Digitally Configurable Outphasing Switched-Capacitor-Based RF Transmitter

A digitally configurable RF transmitter that combines multi-level outphasing and class-G techniques to improve energy efficiency at deep power back-off (PBO) levels is introduced. Each of the two sub-PAs is implemented as a switched-capacitor power amplifier (SCPA); the outputs are combined using an on-chip transformer-based matching network. The outphasing angles are reduced at the PBO levels using multiple vector magnitude values generated using the two sub-PAs. A prototype implemented in a 65nm CMOS process delivers a peak power of 24.5 dBm with an efficiency of 20.3%. With the PA unchanged, the transmitter can be operated in two modes: symmetric multi-level outphasing (SMO) and asymmetric multi-level outphasing (AMO). The measured error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR) are -25 dB (-23.7 dB) and -24 dBc (-24 dBc), respectively, in the SMO (AMO) mode, for a 64QAM 400 kHz (200 kHz) single-carrier signal.