Piecewise Diode-Based Analog Predistorter for High-Accuracy Wideband RF Power Amplifier Linearization

This work presents an analog pre-distortion (APD) linearizer that employs a piecewise linear shape to accurately approximate the nonlinear inverse characteristics of a power amplifier (PA). The APD amplitude characteristic is realized using a cascade of two nonlinear diode impedances, designed to enter conduction at different input amplitudes. The APD phase characteristic is achieved with a dual-branch architecture, a delay line, and an attenuator. The APD bandwidth is 3 to 5 GHz, and it is able to replicate the inverse PA characteristics with a gain error of 0.2 dB, and phase error of 0.4$^\circ$ at 3.8 GHz. As compared to the PA-only case, this APD improves by up to 21 percentage points the normalized root mean square error (NRMSE) and by up to 14 dB the adjacent channel leakage ratio (ACLR). With its wideband, DPD-like performance, this piecewise APD offers a viable replacement for digital linearizers.