On The Robustness of ACLR and EVM Performance in Hybrid Digital/Analog Predistorters

Digital predistortion (DPD) is the most widely used technique for linearizing power amplifiers. However, the increasing demand for high-bandwidth applications poses a challenge for traditional DPD as it usually entails oversampling a signal by up to five times its bandwidth. To address this, hybrid DPD techniques, which split the predistortion algorithm between the digital and analog domains, offer a promising solution. This study evaluates the robustness of a hybrid digital/analog predistorter in terms of its error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR) performances. Specifically, it examines the impacts of a limited gain resolution in the analog predistortion implementation and imperfect delay matching between the input and control signals of the analog predistortion function. These effects were first considered independently of each other. Later, the performance of the linearized amplifier was assessed in presence of both imperfections. The findings show that the ACLR is sensitive to an imperfect implementation of the analog predistortion function. However, the EVM performance is much more resilient to such imperfections.