Loop Delay Correction for Adaptive Digital Linearization of Power Amplifiers

As one of the most common linearization techniques, adaptive digital predistortion minimizes the difference between the input signal of the predistorter and the feedback signal from the power amplifier. The loop delay between these two signals must be controlled precisely so that the convergence of the predistorter should be assured. In this paper a novel two-stage loop delay correction scheme is presented. In the first stage, the integer delay between the input signal and the feedback signal is estimated based on the cross-correlation of them. In the second stage, the fractional delay between these two signals are corrected by a delay lock loop (DLL) circuit, in which a novel timing error detector used as the discriminator is proposed. The proposed loop delay correction scheme is applied to an adaptive digital predistorter in an orthogonal frequency-division multiplexing (OFDM) system. Simulation results show that the proposed loop delay correction method eliminates the loop delay perfectly, so that nearly optimal power spectral density (PSD) performance is achieved and a high degree of linearization is realized.