Computationally Efficient 2-D Predistortion for Multi-Carrier Envelope Tracking Power Amplifiers

An efficient, model based, digital predistortion (DPD) is presented for high efficiency wide bandwidth envelope tracking (ET) power amplifiers (ETPA) with multi-carrier results. This ET configuration is specifically designed for wideband carrier aggregation (CA) signals that have >200MHz bandwidth and high peak to average ratio. The DPD is based on a new formulation of the inverse RFPA surface which enables improved sparse signal processing techniques. 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 724, while achieving reduced spectral emissions, improved computational efficiency, linearity and power efficiency. These improvements are achieved by calculating the covariance matrix within the Doubly Orthogonal Matching Pursuit (DOMP) algorithm to assist with parametric estimation through Reduced Computation-DOMP (RC-DOMP) to replace the Moore-Penrose inverse. With all these techniques, we can perform parameter estimation updates within 1 second on a Xilinx ZCU208 RFSOC achieving specification compliant performance, enabling future efficient real time closed loop operation. Measurements of a 4 CA signal with over 200MHz signal bandwidth, around 3.7 GHz is presented, with peak to average ratio of 6dB after crest factor reduction, Po>38.9dBm, EMV <4%, and <-35dBc spectral regrowth with DPD.