Digital Predistortion for Wide Dynamic Power Range Quadrature Switched-Capacitor Power Amplifiers Using Self-Adaptive Residual LSTM Neural Network

In modern intelligent wireless communication systems, the transmission configurations of radio frequency (RF) power amplifiers (PAs)—most notably transmit power— dynamically change across a wide range to accommodate various service scenarios and currently available communication resources, posing new challenges for digital predistortion (DPD). Traditional DPD solutions are primarily designed for scenarios where PAs operate at a constant average power level (PL) and thus cannot be directly applied, as the PA is a dynamic nonlinear system significantly influenced by PLs. To address this issue, a self-adaptive residual long short-term memory (SAR_LSTM) neural network (NN) is proposed in this article for wide dynamic power range quadrature switched-capacitor PAs (SCPAs). The proposed model adopts a two-stage approach comprising a power variation module (PVM) and a residual LSTM (R_LSTM). In the first stage, the PVM generates a power variation-dependent feature vector, which is then multiplied with the original input signal. In the second stage, the adjusted input signal passes through the R_LSTM to perform the corresponding predistortion calibration. This process tightly integrates the underlying causes of power variation in the SCPA circuit with our model, enabling highly accurate self-adaptive calibration across a wide dynamic power range without requiring parameter updates. In the measurement, a 15-bit transformer-based quadrature SCPA chip with Class-G and IQ-cell-sharing techniques is implemented in a 28-nm CMOS process and employed to verify our method. For the 802.11ax 40-MHz 64-QAM signal at 2.4 GHz, experimental results demonstrate that the proposed model achieves superior linearization performance compared with state-of-the-art (SOTA) models, with an average adjacent channel power ratio (ACPR) of −39.5 dB and an average error vector magnitude (EVM) of −41.6 dB over a 30-dB dynamic power range.