Conversion analogique-numérique Sigma-Delta large bande appliquée à la mesure des non-linéarités des amplificateurs de puissance

Power amplifiers, which are essential elements of any communication system, will play a crucial role in the development of future communication systems. Today improving power amplifiers requires technological advances at the circuit device level, but one also must consider a more global approach. In particular, advances in digital processing can now correct in the early stage of the communication chain some distortions that are generated downstream in the chain. Digital pre-distortion is a correction technique for power amplifiers that has a growing interest because of its completely digital implementation and of its gains in linearity and energy consumption. This technique requires a feedback path where the analog-to-digital converter is a critical element. This component must satisfy the constraints of high resolution , wide bandwidth, and high linearity. In this thesis, we propose a new architecture of analog-to-digital converter based on bandpass Delta-Sigma modulators. This architecture takes advantage of operating bandpass modulators that are designed to work in parallel, each focusing on different frequencies, but also of a particular cascading arrangement to eliminate the useful signal, which has a high power, in order to reduce dynamics constraints. High-level design and simulations were carried out for discrete time and continuous time systems and also required the development of appropriate simulation tools.Les amplificateurs de puissance, éléments constitutifs essentiels de tout système de télécommunication, vont jouer un rôle capital dans le développement des futurs systèmes de communication. Aujourd'hui l'amélioration des amplificateurs de puissance nécessite un progrès technologique au niveau du composant lui même mais doit aussi tenir compte d'une approche plus globale. En particulier, le progrès dans les traitements numériques permet aujourd'hui de corriger en amont certaines distorsions qui seront générées en aval de la chaîne de communication. La pré-distorsion numérique est une technique de correction des amplificateurs de puissance qui connaît un intérêt grandissant de par son intégration complètement numérique et par les gains en linéarité et en consommation. Cette technique nécessite une voie de retour dont un élément critique est le convertisseur analogique-numérique. Ce composant doit répondre à des contraintes de résolution, de bande passante et de linéarité élevées. Dans cette thèse, nous proposons une nouvelle architecture de convertisseur analogique-numérique à base de modulateurs Sigma-Delta passe-bande. Cette architecture tire partie du fonctionnement passe bande des modulateurs que nous faisons travailler en parallèle, chacun centré sur différentes fréquences, mais aussi d'un agencement en cascade particulier pour éliminer le signal utile, qui est de forte puissance, dans le but de diminuer les contraintes de dynamique.La conception haut niveau et les simulations ont été menées pour des systèmes à temps discret et aussi à temps continu et a nécessité le développement d'outils adaptés de simulation se basant sur la boîte à outils Delta Sigma Toolbox de Richard Schreie

ワイヤレス通信のための先進的な信号処理技術を用いた非線形補償法の研究

The inherit nonlinearity in analogue front-ends of transmitters and receivers have had primary impact on the overall performance of the wireless communication systems, as it gives arise of substantial distortion when transmitting and processing signals with such circuits. Therefore, the nonlinear compensation (linearization) techniques become essential to suppress the distortion to an acceptable extent in order to ensure sufficient low bit error rate. Furthermore, the increasing demands on higher data rate and ubiquitous interoperability between various multi-coverage protocols are two of the most important features of the contemporary communication system. The former demand pushes the communication system to use wider bandwidth and the latter one brings up severe coexistence problems. Having fully considered the problems raised above, the work in this Ph.D. thesis carries out extensive researches on the nonlinear compensations utilizing advanced digital signal processing techniques. The motivation behind this is to push more processing tasks to the digital domain, as it can potentially cut down the bill of materials (BOM) costs paid for the off-chip devices and reduce practical implementation difficulties. The work here is carried out using three approaches: numerical analysis & computer simulations; experimental tests using commercial instruments; actual implementation with FPGA. The primary contributions for this thesis are summarized as the following three points: 1) An adaptive digital predistortion (DPD) with fast convergence rate and low complexity for multi-carrier GSM system is presented. Albeit a legacy system, the GSM, however, has a very strict requirement on the out-of-band emission, thus it represents a much more difficult hurdle for DPD application. It is successfully implemented in an FPGA without using any other auxiliary processor. A simplified multiplier-free NLMS algorithm, especially suitable for FPGA implementation, for fast adapting the LUT is proposed. Many design methodologies and practical implementation issues are discussed in details. Experimental results have shown that the DPD performed robustly when it is involved in the multichannel transmitter. 2) The next generation system (5G) will unquestionably use wider bandwidth to support higher throughput, which poses stringent needs for using high-speed data converters. Herein the analog-to-digital converter (ADC) tends to be the most expensive single device in the whole transmitter/receiver systems. Therefore, conventional DPD utilizing high-speed ADC becomes unaffordable, especially for small base stations (micro, pico and femto). A digital predistortion technique utilizing spectral extrapolation is proposed in this thesis, wherein with band-limited feedback signal, the requirement on ADC speed can be significantly released. Experimental results have validated the feasibility of the proposed technique for coping with band-limited feedback signal. It has been shown that adequate linearization performance can be achieved even if the acquisition bandwidth is less than the original signal bandwidth. The experimental results obtained by using LTE-Advanced signal of 320 MHz bandwidth are quite satisfactory, and to the authors’ knowledge, this is the first high-performance wideband DPD ever been reported. 3) To address the predicament that mobile operators do not have enough contiguous usable bandwidth, carrier aggregation (CA) technique is developed and imported into 4G LTE-Advanced. This pushes the utilization of concurrent dual-band transmitter/receiver, which reduces the hardware expense by using a single front-end. Compensation techniques for the respective concurrent dual-band transmitter and receiver front-ends are proposed to combat the inter-band modulation distortion, and simultaneously reduce the distortion for the both lower-side band and upper-side band signals.電気通信大学201

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

Novel power amplifier design using non-linear microwave characterisation and measurement techniques

This thesis, addresses some aspects of the well-known, problem, experienced by designer of radio frequency power amplifiers (RFPA): the efficiency/linearity trade-off. The thesis is focused on finding and documenting solution to linearity problem than can be used to advance the performance of radio frequency (RF) and microwave systems used by the wireless communication industry. The research work, this was undertaken by performing a detailed investigation of the behaviour of transistors, under complex modulation, when subjected to time varying baseband signals at their output terminal: This is what in this thesis will be referred to as “baseband injection”. To undertake this study a new approach to the characterisation of non-linear devices (NLD) in the radio frequency (RF) region, such as transistors, designated as device-under-test (DUT), subjected to time varying baseband signals at its output terminal, was implemented. The study was focused on transistors that are used in implementing RF power amplifiers (RFPA) for base station applications. The nonlinear device under test (NL-DUT) is a generalisation to include transistors and other nonlinear devices under test. Throughout this thesis, transistors will be referred to as ‘device’ or ‘radio frequency power amplifier (RFPA) device’. During baseband injection investigations the device is perturbed by multi-tone modulated RF signals of different complexities. The wireless communication industry is very familiar with these kinds of devices and signals. Also familiar to the industry are the effects that arise when these kind of signal perturb these devices, such as inter-modulation distortion and linearity, power consumption/dissipation and efficiency, spectral re-growth and spectral efficiency, memory effects and trapping effects. While the concept of using baseband injection to linearize RFPAs is not new the mathematical framework introduced and applied in this work is novel. This novel approach NOVEL POWER AMPLIFIER DESIGN USING NON-LINEAR MICROWAVE CHARACTERISATION AND MEASUREMENT TECHNIQUES CARDIFF UNIVERISTY - UK ABSTRACT vi has provided new insight to this very complex problem and highlighted solutions to how it could be a usable technique in practical amplifiers. In this thesis a very rigorous and complex investigative mathematical and measurement analysis on RFPA response to applied complex stimulus in a special domain called the envelope domain was conducted. A novel generic formulation that can ‘engineer’ signal waveforms by using special control keys with which to provide solution to some of the problems highlighted above is presented. The formulation is based on specific background principles, identified from the result of both mathematical theoretical analysis and detailed experimental device characterisation

Impact of subband quantization on DPD correction performance

International audienc

Impact of subband quantization on DPD correction performance

International audienceThe digital predistortion (DPD) is a technique to linearize the response of power amplifiers which is the subject of an active research. In order to model accurately and properly linearize the PA, the ADC in the feedback path must digitize the distorted signal with an adequate resolution and bandwidth. The multi-stage noise band cancellation (MSNBC) ΣΔ architecture is able to provide a signal digitized by subbands and where the subbands may be digitized with different resolutions. We show that the correction performance can be maintained while different quantization for the main high power subband and for the low power subbands are used resulting in a more flexible and low power consumming solution