A study on the frequency response compensation for Envelope Amplifiers in EER Power Amplifiers

The Envelope Elimination and Restoration Power Amplifier (EER-PA) and the Envelope Tracking Power Amplifier (ET-PA) have attracted significant attention because of their capability of high efficiency under back-off operation. In EER-PAs or ET-PAs, the performance of Digital Pre-Distortion (DPD) is degraded due to their tendency towards high nonlinear behavior including frequency response of the envelope amplifier compared to conventional power amplifiers. Therefore, memory DPD is indispensable for EER-PAs or ET-PAs. In this paper, we clarify the degradation mechanisms of the DPD for an EER-PA using two-tone test measurement results, and verify an analytical model for improving the performance of the DPD. The performance of the simple combined technique of memoryless DPD and frequency response compensation is confirmed by using a prototype EER-PA. The Adjacent Channel Leakage Power Ratio (ACPR) is improved from −21.1 dBc to −42.9 dBc for an OFDM signal with 2.7 MHz bandwidth.