| Power amplifiers deployed in radio frequencies communication systems introduce generally distortions to their input signals. Such distortions compromise greatly the quality of the voice and data at the receiver side. In this thesis we report a comprehensive study of linear and non-linear distortions sources that influence the behaviour of RF power amplifiers along with the means of minimizing and/or compensate their effects.; In the first part of this report, a realistic, accurate, versatile, and thermal-free complex behaviour test bed suitable for the characterization of third-generation power amplifiers (PA) is proposed.; The linearized PA output spectrum and Error Vector Magnitude (EVM) show a significant performance improvement in the temperature compensated predistortion function over a memoryless one. The results of the measurements that have been conducted on the LDMOS PA are in agreement with those obtained from simulations using the developed PA and the predistorter models implemented in Advanced Design System (ADS) environment. Moreover, electrical memory effects, due to the frequency variation of impedances at the gate and drains nodes over the modulation bandwidth of the PA input signal, has been examined.; The characterization results obtained by the test bed have been used to design a digital predistorter for the LDMOS amplifier. An accurate algorithm intended for the synthesis of predistortion function is presented. Indeed, a memoryless digital predistorter lookup table is directly synthesized using the measured AM/AM and AM/PM curves without any need to perform additional analytical derivations and/or numerical optimizations. The predistorter synthesis procedure requires a single iteration, contrary to previous approaches, which required several iterations to obtain similar performance. This constitutes an important contribution to the digital predistortion technology. Measurement results, under different signal excitations such as CDMA2000 and multi-tones, show great improvement in the out-of-band spectrum regrowth at the high-power-amplifier output. Two schemes are proposed, (i) baseband, and (ii) bandpass RF for the implementation of digital predistorters. These two schemes are compared with respect to the measured performance of the correspondent prototype implementations using FPGA, DSP, fast AID and D/A converters. (Abstract shortened by UMI.)... |
