Adaptive predistortion linearization of RF power amplifiers using lookup tables generated from subsampled data

Abstract

This paper discusses a new architecture for adaptive predistortion linearization of power amplifiers, whereby subsampled data (i.e. lower than Nyquist rate) from the input and output baseband waveforms is used to construct a lookup table. The technique utilizes a sampling downconverter that accurately captures a waveform sample in a narrow aperture before digitization. Because aliasing effects are the same for both input and output waveforms, information may be obtained regarding the amplitude and phase distortion characteristics of the power amplifier. The concept is validated using a test bed consisting of two sampling downconverters and a dual channel receiver. Results achieved indicate that 10-12 dB of adjacent channel power ratio (ACPR) improvement may be obtain using sampling rates as low as 33% of the Nyquist rate of the baseband output signal bandwidth.