A Robust Augmented Combination of Digital Predistortion and Crest Factor Reduction for RF Power Amplifiers

This paper proposes a robust combination of digital predistortion (DPD) and crest factor reduction (CFR) for radio frequency (RF) power amplifiers (PAs). It is constructed using the architecture of CFR-DPD connected with a compensation module (CM). The compensation module is introduced to achieve mutual compensation between the output signals of CFR and DPD, and this can reduce the damage to the signal by CFR. The combination of CFR-DPD-CM provides the means to exploit margins in the transmitter performance, allowing the tradeoff among peak-to-average power ratio (PAPR), adjacent channel power ratio (ACPR) and error vector magnitude (EVM). The proposed combination of CFR-DPD-CM is assessed using a GaN Class-F PA driven by two modulated signals (a 4-carrier OFDM signal and a WCDMA 1001 signal with 20-MHz bandwidth), and a GaN Doherty PA driven by a 15-MHz long-term evolution (LTE) signal. The experimental results show that when the CFR reduces the PAPR about 4 dB, applying the proposed combination of CFR-DPD-CM, the average reduction of ACPR is 5.12 dB, and the average reduction of EVM is 1.26% compared with the conventional architecture of CFR-DPD.