An Out-of-Band Digital Predistortion Scheme and Its Verification for Power Amplifiers with Strong Nonlinearity

Conventional full-band (FB) digital predistortion (DPD) methods have limited linearization performances in terms of the adjacent channel power ratio (ACPR) and normalized mean square error (NMSE) when the nonlinearity of power amplifier (PA) is considerably strong. In this paper, an out-of-band (OOB) DPD scheme is proposed for the PA with strong nonlinearity. This OOB DPD scheme only suppressing the OOB nonlinear distortion, and it significantly improves the performance of ACPR even in the context of strong nonlinearity. Experimental results verify that the proposed OOB DPD can improve the ACPR performance by 20 dB when the PA is driven to the strong nonlinearity of −25 dBc ACPR. Moreover, even if the PA is driven to −20 dBc ACPR where the PA reaches saturation on the signal peak, the proposed OOB DPD still effectively suppresses the partial OOB distortion by 19 dB.