Research Topics

RF circuits design and test
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Last update 09 Jan 2015


Coordinator: Hatem Trabelsi

Permanent members: Ghazi Bouzid, Ayadi Rim.

Thesis Members: Amel Neifar, Imen Barraj, Intissar Toihria.

Master Members: 

Undergraduate Members:




Introduction to the research topic


The aim of our research is to contribute to the design of high performance, low complexity, energy-efficient radio frequency integrated circuit operating:

-        In the 863-870 MHz Zigbee for wireless sensor applications

-        In the 3-5GHz ultra wide band (UWB) for healthcare devices

-        In the 3-10 GHz (UWB) IEEE 802.15.4a standard for medical telemetry

-        In the unlicensed 2450 MHz band and uses the new chirp spread spectrum (CSS) technique as set by IEEE 802.15.4a standard.

Our main mission is to develop innovative systems with low cost and low consumption from conventional CMOS technologies. The team works in the field of microelectronics applied to the treatment of analog and digital signal.



Activities Summary:


Subject 1 : Design and modeling of radio frequency electronic systems for wireless sensors

Members : Hatem Trabelsi (HDR)

Abstract:  The aim of my research is to contribute to the design of high performance, low complexity, energy-efficient radio frequency integrated circuit operating in the ultra wide band (UWB) or using the IEEE 802.15.4a standard and intended to be used in wireless sensors network for healthcare applications.

The continuing trend of miniaturization of microelectronics and recent advances in MEMS (Micro Electro Mechanical Systems), combined with advances in the design of radio frequency electronics has led to the emergence of a new class of electronic systems with one or more sensors. When implanted and activated, these systems form wireless sensor networks (WSN). However, because of their characteristics (energy constraint, reduced capacity of nodes, large number of sensors ...), reducing the power consumption of these sensors is a scientific challenge.

The objective of this research works is to design an innovative solution for the transceiver part of a wireless sensor device that maximize the autonomy in a network operating in the ultra wide band UWB or using the IEEE 802.15.4a standard and dedicated for healthcare applications.

This work was initiated within the framework of collaboration between EMC ("Electronique Micro-technologie & Communication") of the ENIS, the company “Siemens Building Technologies, Fire and Security Products, GmbH & Co. OHG, Germany” specialized in the development of RF circuits operating in networks for security applications and BEBCOM-TECHNOLOGY which is a design center of Analog, UWB RF CMOS circuits, MEMS sensors and computer aided design.

To achieve this goal, the research undertaken aimed to initially define the specifications and needs of a wireless sensor in terms of performance, circuit complexity and necessary functions. Of course, the choice of technology and problems induced by the use of a standard CMOS technology has been considered.

Each block of the transceiver channel has been modeled and simulated in ADS tool in order to determine its approximate parameters. Then a co simulation was conducted to evaluate the bit error rate (BER : Bit Error Rate). It is done with the analog receiver and a non coherent demodulator suitable for low power implementation.

The continuation of my research work should focus on tow topics:

- The complete design of the dual band 3-5 GHz FSK IR-UWB transceiver integrated circuit at transistor level using 0.65µm CMOS.

-. Design and validation of various elements of transceiver operating in the unlicensed 2450 MHz band and uses the new chirp spread spectrum (CSS) technique as set by IEEE 802.15.4a standard. This targets other types of applications requiring longer ranges and communications of devices moving at high speeds, such as moving vehicles monitoring, alarm systems for predicting vehicles’ collision, and vehicle-to-vehicle communication.



Subject 2 : Design of UWB systems

Members : Imen Barraj (Thesis)

Abstract: Ultra-wideband radio (UWB) is a rapidly developing wireless technology that promises both low and high data rates for short-range commercial radios. These benefits stem from the use of wide bandwidths and impulse signaling, implying high channel capacity and precise time resolution. UWB has been used for military radar and imaging since the 1950's, however, in 2002 the Federal Communications Commission (FCC) approved the use of the 3.1-10.6GHz band for unlicensed UWB applications. The restriction on transmitted power spectral density in this band is equal to -41.3dBm/MHz.

This thesis covers the aspects of pulse generation for pulsed UWB communication by exploring tradeoffs that can be made in the pulse shaping in order to reduce power consumption in the transmitter and ensuring a better spectral efficiency of the FCC mask. The designed generator is based on carrier topology. It consists of using an up-conversion mixer and local oscillator (LO) to transpose a baseband pulse in the frequency band of operation. This method is appreciated since it present an efficient tuning capability of the spectrum and the problem of power consumption can be solved using LO switching circuit. Therefore, we have investigated ways to shape and generate pulses optimally within the UWB band. A Gaussian pulse shape is optimal for minimizing the mask loss power inside the emission mask, however the shape is costly to generate with CMOS low power circuits and has several limitations that make it undesirable for implementing in UWB transceivers. A rectangular pulse shaping technique seems a good candidate as it ensure a higher spectral efficiency compared to the Gaussian an triangular but it present stronger sidelobes in the spectrum which should be filtered, resulting in poor system efficiency while increasing the system complexity. The implementation of the triangular pulse is easier using low power circuits but its performances are limited in terms of spectral efficiency. In order to ensure a better spectral efficiency, we introduce a new pulse shape called modified triangular pulse (MTri). Compared to the spectrum of the encountered wavelets, MTri pulse allows a more flattens spectrum, ensuring a better spectral occupancy specifically at -3dB. This leads to increase both the spectral efficiency and the emitted energy per pulse.

Two pulse generators have been developed. Digital envelope implementation of the baseband pulse is considered allowing tuning capability in magnitude and width. The first generator is adopted to OFDM and DS systems. It generates OOK modulated pulses in the 3-5GHz band, targeting high data rate applications. The consumed energy per pulse is 12.82pJ and 19.8pJ for DS and OFDM systems, respectively. The proposed architecture is well suitable for communication with an energy detection which promises low complexity, low power and low cost. The pulse spectrum is programmable in center frequency and pulse width. The second architecture is dedicated to IEEE 802.15.4a standard. To meet the standard requirements, a new concept of the pulse generator based on temporal overlap using four pulse elementary generators operating in parallel is introduced. This allows bursts generation compatible with the PHY layer of the IEEE 802.15.4a  standard. The power consumption is 7.24mW for a pulse repetition frequency of 500MHz. The generated UWB pulses within the two generators complies with the FCC regulation while ensuring better spectral efficiency. The amount of sidelobe rejection factor is important to avoid the adjacent channel interferences. The MTri pulse spectrum provide a good sidelobe suppression of 24 dB which avoid the spectrum to be filtred.



Subject 3 : Design of UWB systems

Members : Amel Neifar (Thesis)

Abstract: For over ten years, many industrial and scientific applications have been developed in the medical field. Among these applications is actimetry which allows providing an objective measure of motor activity of a patient using wireless sensors and technical communications. The majority of the solutions implemented for the transport of medical data from the actimeter to the server of the patient were based on the use of a cable network whose main drawbacks are its size and cost, and the use of electrodes or external wireless sensors to capture vital signs.

Nowadays, in order to overcome these shortcomings, the trend is to replace these cables with wireless connections, and to achieve monolithic circuits that integrate the RF part and the wireless sensors on the same silicon chip.

In our research, we try to study the RF part of the actimeter, specifically the transmission system. We are particularly interested in the study of the mixer in the transmission chain as well as the local oscillator which will perform the transposition operation. Ultra wideband is used as modulation technique under the IEEE 802.11.4a standard.



Subject 4 : Conception d’un modulateur numérique pour une chaîne de transmission RF (in French)

Members : Ghazi Bouzid: (HDR)

Abstract: Dans le cadre de cette thèse nous s’intéressons à l’étude et à la conception d’un modulateur numérique pour une chaîne de transmission RF. La première partie du travail demandé est l’étude des avantages et des inconvénients des différentes architectures radio afin de choisir une architecture convenable à notre application. La deuxième partie du travail demandé est l’étude des différents types de modulation/démodulation possibles pour la communication sans fil (ASK, 2FSK, BPSK, QPSK, OQPSK, DQPSK, etc.). Une étude détaillée sur les modulations a enveloppe constante nous a permis de choisir la modulation de fréquence (BFSK Binary Frequency Shift Keying) puisque elle permet d’utiliser un amplificateur de puissance non linéaire. Nous avons commencé la validation fonctionnelle du modulateur/démodulateur dans la chaîne de transmission RF complète ainsi que l’extraction de ces performances. Nous avons utilisé le logiciel ADS pour achever cette étape. Une étude détaillée sur les techniques d'étalement du spectre nous a permis de choisir la méthode du saut de fréquence (FHSS frequencies hopping spread spectrum). Nous avons commencé aussi la mise en œuvre du bloc DDFS qui nous permet de générer les fréquences du saut.

Pour achever les travaux de thèse nous devons faire l’étude de l’électronique associée au modulateur/démodulateur qui comporte une partie de codage, une partie de modulation numérique et une partie de transposition de fréquence ainsi que la conception et la simulation au niveau transistor de ses différentes sous fonctions. Nous allons utiliser le logiciel Cadence pour achever cette étape.



Subject 5 : Etude et conception d’un protocole de communication dans un réseau de capteurs RF intelligents autonomes (in French)

Members : Walid Charfi (HDR)

Abstract: Le travail effectué durant la thèse consiste à concevoir un capteur sans fils autonome et intelligent afin de mettre en place un réseau de capteurs sans fils pour une application domotique. La problématique de conception de réseaux de capteurs sans-fil est un sujet d’intérêt pour SBT. On peut en effet envisager, suite à l’évolution des technologies de communication sans-fil, la nécessité d’une expansion de réseaux. Nous nous sommes donc intéressés au problème de conception d’un protocole de communication de réseaux de capteurs. Le protocole à concevoir devra respecter des contraintes de capacités, de gestion de noeuds, de routage de données, tout ceci à une faible puissance. Essentiellement lorsqu’il s’agissait d’un capteur intégré sur puce selon le concept SoC (System on Chip). On cherche en effet le réseau de coût minimum respectant des contraintes de communication adaptées à un environnement miniature. C’est une étude qui inclut les problèmes de routage avec des contraintes d’intégrité, l’auto-configuration des nœuds et la consommation minimale d’énergie pour augmenter la durée de l’autonomie. Ce problème se présente en différents domaines d’exploitation, c’est pourquoi il est intéressant d’en définir des solutions aussi efficaces que possible.