Digital predistortion with automatic determination of the Crest Factor Reduction gain, principle and experimental validation

Abstract

Digital predistortion (DPD) and Crest Factor Reduction (CFR) are applied separately in radio frequency power amplifiers (PAs) in general. This paper proposes a method to jointly optimize DPD and CFR. For a given model of predistorter our solution gives automatically the Peak to average power ratio (PAPR) reduction gain to be applied by the CFR module. Within the DPD module PAPRs of original input signal and PA output and PAPR at predistorter output without CFR are used to estimate an optimal CFR gain through mathematical calculations. The combined CFR/DPD module ensures that the PAPR at the output of predistorter will not exceed a given limit. Hence, the envelope clipping module which is typically present to protect the PA, may be removed. In addition the proposed method offers a higher operating range of the DPD while fulfilling out-of band requirements and preserving low in-band distortion. Power efficiency of amplification module is improved as well. This solution has been tested by simulation and measurement on a 10-W class AB LDMOS power amplifier.