A +20 dBm Highly Efficient Linear Outphasing Class-E PA Without AM/AM and AM/PM Characterization Requirements

Outphasing Class-E power amplifiers (OEPAs) using isolating power combiners and an inverse cosine signal component separator are inherently linear but suffer from low efficiency at power back-off. For high efficiency both at maximum output power and at power back-off, non-isolating power combiners are required. In this brief the linearity of OEPAs using non-isolating power combiners is studied theoretically and validated by measurement of a 1.8 GHz 20 dBm OEPA implemented in a standard 65-nm CMOS technology using an off-chip transmission-line-based combiner. The developed theoretical model for the linearity is then employed to define digital pre-distortion (DPD) parameters for the implemented OEPA. Using this theory-based DPD and without any AM/AM and AM/PM characterizations, -31 dB RMS EVM level and below -30 dB ACLR were measured for a 13.1 dBm 6.25 MHz 30 Mbit/s 7 dB PAPR 64QAM signal with 41.8% drain efficiency and 33.6% power added efficiency.