Novel Digital Conversion and Power Amplifier Linearization Unit for Wireless Transmitters

Abstract

This article introduces a digital conversion and linearization unit (DCLU) that performs signal conversion and power amplifier (PA) linearization when the digital-to-analog converter (DAC) is constrained by limited bit resolution. The proposed structure applies an error-and-distortion-feedback (EDF) processing principle that integrates re-quantization, noise shaping, and digital predistortion (DPD) within a single digital unit and avoids explicit inverse modeling. The embedded PA forward description uses a polar look-up table (PLUT) representation of the PA static AM/AM and AM/PM characteristics and a linear filter that captures the measured dynamic response. More advanced approaches are also described in terms of incorporating more elaborate forward models within the DCLU, together with a parallel multi-channel realization that relaxes internal clock-rate requirements through time-interleaved processing. The concept is validated through two RF measurement experiments using a 5G New Radio (NR) transmit waveform at 3.5 GHz and 3.6 GHz (NR band n78). The first experiment uses a broadband Gallium-Nitride (GaN) HMC1114 PA to demonstrate the proof of concept and quantify system behavior under reduced bit resolutions. The second experiment uses the Qorvo QPA3503 GaN Doherty PA to evaluate the approach for an amplifier type that is typically more challenging to linearize. The measured results show that the proposed approach maintains good linearization capability under reduced bit resolutions and, in the reported cases, provides improved transmit waveform quality relative to conventional reference DPD schemes, particularly at lower bit widths.