An Experimental Study on Reduced-Complexity Multi-Band Digital Predistorter with a Single Common Feedback Loop

Abstract

This paper proposes how to modify the reduced-complexity multi-band digital predistorter (DPD) with a single common feedback loop we previously proposed, in order to compensate for nonlinear distortions significantly where imperfection of the analog circuit actually exists. Our proposed DPD utilizes a single common feedback loop in order to acquire a feedback signal obtained by overlapping multi-band feedback signals in the frequency domain for adaptive DPD, and compensates for nonlinear distortions using estimated feedback signals obtained by subtracting the transmitting signal on another band from the overlapped feedback signal; this achieves a 63% reduction in complexity. This paper also reveals the mechanism of adjacent channel leakage ratio (ACLR) degradation caused by the imperfection of the analog circuit and the amount of allowed cancellation error in the estimated feedback signals. Our proposed DPD is modified to work well particularly when the gain difference between low and high bands exists in a single common feedback loop that has non-flat frequency response. Some experimental results for a commercial Mini-Circuits wideband power amplifier show that the modified DPD can achieve good ACLR performance significantly with reduced complexity and it is revealed that the modified DPD can work flexibly without dependency on transmitting signal bandwidth.