Multi-level supply-modulated Chireix outphasing for LTE signals

Abstract

This work presents a dynamic characterization of a multi-level Chireix outphasing (ML-CO) power amplifier (PA) with modulated signals. The ML-CO technique combines the advantages of envelope tracking and outphasing architectures by limiting the supply modulation to discrete levels (enabled by an efficient power DAC modulator) and using outphasing for fine amplitude control. We describe the development of an experimental test bench able to supply phase- and time-aligned modulated signals for outphasing and supply modulation simultaneously. Pulse characterization is used to design a multilevel memory-less polynomial DPD. The linearized ML-CO PA is demonstrated with 1.4 MHz and 10 MHz LTE signals at 9.7 GHz. For both signals, the average total power consumption is reduced by a factor of two when supply modulation is used. For the 9.3 dB PAR, 1.4 MHz signal the PA operates with 38% average drain efficiency at 0.54 W average output power.