An Accurate Predistorter Based on a Feedforward Hammerstein Structure

Abstract

This paper presents a feedforward Hammerstein structure that is proposed for the modeling and digital predistortion of the dynamic nonlinear behavior of the wideband radio frequency power amplifiers and wireless transmitters. This model consists of two loops, one used as a signal cancellation loop and the second used as distortion injection loop. The main signal cancellation loop is responsible for the characterizing of the PA dynamics through a Hammerstein model. Indeed, the distortion injection loop was found to complement the main signal cancellation loop by adding an accurate means of modeling the nonlinear dynamics of the intermodulation distorted signal for the better mimicking of the intermodulation distortion products especially in the out-of-band regions. Its accuracy is assessed in behavioral modeling and digital predistortion, by comparing it to other state-of-the-art models. The measurement results show an adjacent channel power ratio of almost $-$ 50 dBc and a normalized mean square error of less than $-$ 42 dB.