Linearization of Phase Modulators in Outphasing Transmitters by Slope-Fit Reordering of Unit Delays

Abstract

Recent advances in CMOS technology have enabled the implementation of high-performance and energy-efficient digital-intensive radio transceivers for fifth-generation (5G) and beyond (6G) wireless communication systems. Among the various transmitter architectures, the outphasing transmitter with constant-amplitude modulation, which allows the use of highly energy-efficient nonlinear power amplifiers, has garnered significant attention since it easily lends itself to a digital-intensive implementation, thus fully exploiting the benefits of scaled CMOS technologies. However, an outphasing transmitter with a delay-based phase modulator suffers from performance degradation due to mismatch-induced static nonlinearity. This paper presents a linearization algorithm that minimizes mismatch-induced static nonlinearity by reordering the unary-weighted delay elements. The effectiveness of this algorithm is demonstrated through simulations and its application to measured delay characteristics from a 22-nm FDSOI CMOS transmitter prototype in a system simulation. The proposed reordering algorithm results in a 7.94% points improvement from 10.63% in EVM and a 7.76dB enhancement from 25dB in ACLR for a 5G NR 64-QAM OFDM waveform with a 200MHz bandwidth.