One-bit in-phase observation for direct learning-based digital predistortion with modified frequency-domain delay estimation and alignment

This article proposes a novel digital predistortion (DPD) implementation method for RF power amplifiers. The new approach adopts only one 1-bit comparator in the feedback path to observe the in-phase (I) or the quadrature (Q) component of the error signal between the input and the output signals. To this end, the theoretical derivation of the in-phase observation based on direct learning architecture (DLA) DPD is first given in this article, by combining the existing 1-bit method and the low-cost in-phase observation. To facilitate the delay estimation and alignment, a modified iterative frequency-domain delay estimation is presented, which only acquires either I or Q components of the output signal to achieve satisfied delay estimation. Experimental results show that the proposed DPD method decreased the normalized mean square error (NMSE) and the adjacent channel power ratio (ACPR) to less than −42 and −51 dB, respectively, which indicates that the proposed DPD system can achieve comparable performance as the existing DPD identification techniques with lower implementation complexity.