Digital Linearization of Wideband Envelope Tracking Power Amplifiers for Mobile Terminals

This article presents a low-complexity linearization method to compensate for multisource nonlinear distortion in wideband envelope tracking (ET) power amplifiers (PAs) for 5G new radio (NR) mobile terminals. The proposed linearization approach consists in an envelope leakage cancellation (ELC) system operating in the dynamic supply path and a 2-D digital predistortion (2-D-DPD) linearizer acting on the baseband complex modulated signal. In a first step, an envelope generalized memory polynomial (EGMP) behavioral model is proposed to compensate for the unwanted radio frequency (RF) leakage that appears at the output of ET modulator (ETM). Then, a baseband 2-D-DPD linearizer based on a slow envelope-dependent generalized memory polynomial (SED-GMP) behavioral model is used to further enhance the linearization performance. The proposed method is validated on a system-on-chip (SoC) ET PA board for mobile applications. The reported experimental results show how the proposed digital linearization approach can mitigate the linearity and efficiency trade-off in ET PAs. Consequently, the out-of-band linearity requirement of - 36 dBc of adjacent channel power ratio (ACPR) is met for 5G-NR test signals with bandwidths ranging from 60 to 200 MHz at 2.55 GHz (band B41), with an overall ET PA power efficiency ranging from 10.1 % and up to 16.5 %, depending on the signal bandwidth.