Conception d’un système de mesure d’enveloppes complexes aux accès de modules de puissance – Application à la mesure du NPR et à la modélisation comportementale d’amplificateurs
Abstract
This work deals with the characterization and the analysis of envelope distortions due to power amplifiers when they are driven by complex modulations. The complex envelope formalism, the main characteristics of modulated signals, the distortion criteria used for nonlinear amplifiers, as well as the characterization method are explained in this report. A calibrated measurement setup has been developed in order to generate and to measure complex envelopes associated with RF modulated signals at input and output ports of power amplifiers under test. The architecture of the calibrated measurement setup, its calibration procedure and the signal processing used for the envelope correction are described. A first application consist in the linearity characterization of multi-carriers amplifiers according to the NPR criterion (Noise Power Ratio). A comparison between the analog and digital approach to measure NPR is performed. That makes it possible to conclude on the spectral design (the number of tones) used for the generation of NPR stimuli to obtain a good NPR accuracy. A second application consists in the use of complex envelop measurements of a power amplifier in order to extract a behavioral model (black box model). An extension to the complex gain is proposed. The nonlinear describing function is fitted by neural networks. This new model takes into account short-term memory effects and constitutes a significant upgrading in system level modeling of non linear equipments
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