Rational Generalized Memory Polynomial for Efficient Predistortion of Wideband Envelope Tracking Amplifiers

Abstract

An improved, efficient, Rational Generalized Memory Polynomial (RGMP) inverse model based, digital predistortion (DPD) is presented for high efficiency wide bandwidth envelope tracking (ET) power amplifiers (ETPA) for wideband carrier aggregated (CA) signals. This ET configuration is specifically designed for wideband carrier aggregation (CA) signals that have 500 MHz corrected bandwidth and high peak to average ratio signals. Term selection is performed with Doubly Orthogonal Matching Pursuit (DOMP), an efficient sparse signal processing technique. This algorithm has been implemented for open loop and a batch mode closed loop operation. This model and these techniques reduce the number of inverse model terms significantly, using <40 terms of hundreds, while achieving improved spectral emissions, with computational efficiency, output signal fidelity and improved power efficiency. These algorithms are evaluated on a Gen 3, Xilinx ZCU208 RFSoC, achieving specification compliant performance, enabling future efficient real time closed loop operation. Measurements of a 2CA (PAPR=4.2dB) and 4CA (PAPR=6dB) signal with up to 500 MHz signal bandwidth on a Wolfspeed CG2H40025 GaN device around 3.7 GHz are presented. The 2CA signal, with peak to average ratio (PAPR) of 4.2dB after crest factor reduction achieves Po>41.2dBm, NRMSE <2%, and <-40dBc spectral regrowth with Adagio™ DPD.