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This paper presents a new driving method allowing fast analogue light modulation with bistable ferroelectric liquid crystals (FLC). The method is evaluated using a functional virtual prototyping design flow. First, a surface stabilized binary FLC cell is modeled in VHDL-AMS language on the basis of well-known theories of FLC. Some physical and environmental phenomena are added (e.g. electronic behavior of the cell, temperature, etc.) in order to improve its reliability. Once the model is validated, a virtual prototype of a FLC pixel is performed by associating the model of the FLC cell and the model of an appropriate wave generator. Simulations show that our new driving method works, but with certain limitations. The most critical one seems to be the high temperature dependence of the pixel response.

The tendency today is to replace high-dynamic light modulators by high-speed binary ones (of which the micromirror is the best example). This kind of spatial light modulators (SLM) fulfils all the present needs in displays. They are used in optical communications as binary systems and also in display applications (video projectors) with temporal multiplexing, in order to generate greyscale or colour images. In optical processing, and in the majority of coherent applications, temporal dithering introduces some distortions. In this paper, this point is studied with simulations. We point out that temporal multiplexing cannot be used in the Fourier plane. In the imaging plane, the distortion is weak if the filter has a positive impulse response.

International audience; The assembly within a single optoelectronic interconnect module of different components, including vertical-cavity semiconductor lasers and photodiode arrays, optical fibers, and electronics implying electrical, optical, mechanical, and thermal interactions, introduces new constraints in the conception phase and necessitates a new and different approach for modeling and simulation. A promising solution, when conceiving optoelectronic microelectromechanical systems, is obtained by simulation with the multilevel language VHDL-AMS based on system component parameters and standards.

Il existe une nouvelle approche methodologique en conception assistee des systemes complexes, utilisable notamment en electronique de puissance. La schematique classique a des limitations intrinseques, que cette avancee peut repousser. Le langage normalise VHDL-AMS propose des mecanismes avances qui restent meconnus et tres largement sous-utilises. Ils permettent la mise en œuvre des meta-schemas et de leur configuration. Cette approche, une fois maitrisee, ouvre la porte a des ameliorations methodologiques dont toutes les consequences benefiques restent a explorer.

International audience; Image rendering of spatial light modulators (SLMs) is often degraded by various effects. Some efficient methods to get around nonuniformity, nonlinearity, and remanence and improve image rendering are presented. Optical laboratory results are presented for an analog ferroelectric liquid-crystal SLM using a high-speed camera. Focus is made on a preprocessing compensation method, using a spatialdependant correction table. A high-speed "on-the-fly" implementation is also suggested.

This paper presents a hybrid processor dedicated to the reconstruction algorithm in multislice spiral computed tomography. The described architecture focuses on the advanced single-slice rebinning algorithm, which is a basic 2-D-to-3-D rebinning method developed in 2000. The hybrid processor is composed of four cores (rebinning, filtering, backprojection, and interpolation), including an optical processor for the backprojection. The system is modeled with a multi-abstraction-level approach. The model permits one to evaluate the dependence of both the reconstruction quality and the computation time with different parameters (reconstruction parameters, device features, etc.). It is used in a substantial simulation process allowing the identification of predominant degradation sources and the evaluation of their impact, and leading to the specification of each subsystem. A prototype of each core has been realized. The optical core has been identified as the most critical element, although results are very encouraging. This study has underlined that a computational speedup of more than two orders of magnitude could be reached. This is expected to be very useful for future challenging applications in the field of image-guided computer-assisted surgery, where the reconstruction rate would become critical to ensuring acceptable responsiveness.

In this study, we expose new approaches to design and optimize systems at a high level description using Very High Speed Integrated Circuit Hardware Description Language for Analog and Mixed Systems (VHDL-AMS) standard. We detail a theoretical approach to develop self-tuned VHDL-AMS models and we expose some simulations obtained after the optimization of a fractional- N frequency synthesizer's performances used for wireless systems. The applied optimization method uses the “experience plans” with seven generics having in view to minimize the loop response time and the synthesizer output frequency.

A VHDL-AMS model of a surface-stabilized ferroelectric liquid crystal cell is presented in this paper. The model is based on the uniform FLC theory known since 1990. Although not quantitative, this approach gives us a good idea of the behaviour of such crystals. The model will be characterized and the results will be compared. Many related phenomena (effect of the temperature, ion transport...) will be introduced to complete the behavioural description. The purpose of this work is the design of virtual prototype for a high-speed spatial light modulator.

L es differentes disciplines de l'electronique utilisent, a des degres tres varies, des outils et des flots de conception assistes par ordinateur. Mais si on considere l'electronique de puissance, les convertisseurs statiques sont concus en grande partie grâce a l'experience aiguisee des ingenieurs et par la mise au point de prototypes bases sur des cycles de detection et de correction d'erreurs. La conception se deroule par etapes de dimensionnement des differentes par- ties du convertisseur, mais n'est pas assistee par ordinateur, si ce n'est quelques calculs ou la recherche dans des bases de donnees. Tout d'abord, l'ingenieur.

In this paper, a new laser diode model is presented including electrical, thermal and optical behaviors. This kind of model is feasible due to the high potential of VHDL-AMS in mixed technology modeling. When simulating, quantities like current, voltage, dissipated thermal power, junction temperature, optic power and wavelength are calculated simultaneously. Interactions between these parameters are taking into account and equations are near physical laws. Simulation results show static and dynamic characteristics and temperature effects.

This paper presents a VHDL-AMS description of a direct torque control (DTC) of an asynchronous machine and exposes some high-level-simulation results allowing a behavioral study with a virtual way. A DTC control is a multi-domain system including digital and analogue electronics power, an electrical motor and sensors. So that its simulation presents some difficulties. A VHDL-AMS description provides a good solution to solve this problem and permits to predict system performances when modifying its parameters.

This paper presents a behavioral model library of analogue and mixed circuits used in the radio-frequency domain. The models are described in VHDL-AMS and are carefully documented and validated, in order to be easily used by designers or model developers. These models allow one to explore systems architecture easily and rapidly.

The paper presents the model of a complete multidomain system involving two opto-electronic components : the emitter (laser diode) and the receiver (photo-diode). It is written in Anacad Mentor Graphics HDL-A and integrates the propagation environment characteristics (optical fiber and vacuum) and the thermal behavior of each component. First, packages describing electrical (current/voltage), optical (light power/ wavelength), and thermal (heat flow/temperature) domains are detailed. Second, the models of the components are explained. They include an electrical, a thermal and an optical part, the latter being particularly developed. Third, the models of the propagation environment, an optical fiber and the related free space, are presented. The components are assembled to build a complete instrumented opto-electronic transmission system. The laser diode emits a digital clock through an optical fiber to a photodiode. The laser diode is thermal controlled through a Peletier module, which can be deactivated as needed. The alignment of the laser diode with the optical fiber can be studied/modified too. The HDL-A resulting models have been simulated in the ELDO environment. Results show that thermal variations influence the quality of the transmission. It has also been translated into VHDL-AMS and proven syntactically correct. It now waits for a full-featured VHDL-AMS simulator...

Optical processing can be used to speed up some algorithms of image reconstruction from tomodensitometric data provided by volume exploration systems. This may be of high interest in order to meet the needs of future assisted therapy systems. Two systems are described in this document, corresponding to the two main steps of the above mentioned algorithms: a filtering processor and a backprojection processor. They are first considered under a material point of view. Whatever function it may compute, an optical processor is made up of light sources, displays and cameras. Present state-of-the-art devices highlight a weakness in display performances. Special attention has been focused on ferroelectric liquid crystal spatial light modulators (modelling, simulations, and characterizations of commercial solutions). The potential of optical architectures is compared with electronic solutions, considering computation power and processed image quality. This study has been carried out for both systems first in simulation, with a reliable model of the architecture, and then with an experimental prototype. The optical filtering processor does not give accurate results: the signal to noise ratio on the reconstructed image is about 20 dB in simulation (the model used does not take into account the majority of geometrical distortions) and experimental measurements show strong limitation, especially when considering the problem of image formation with coherent lighting (speckle). On the other hand, results obtained with the optical backprojection processor are most encouraging. The model, more complete and accurate than the filtering processor, as well as the simulations, shows that processed image quality can be virtually equivalent to the one obtained by digital means (signal to noise ratio is over 50 dB) with two order of magnitude speed-up. Results obtained with the experimental prototype are in accordance with simulations and confirm the potential held by the architecture. As an extension, a hybrid processor involving the backprojection processor for the computation of more complex reconstruction algorithms, e.g. ASSR for helical CT-scan, is proposed in the last part of the document., Le traitement optique des données tomodensitométriques fournies par les systèmes d'exploration volumique pourrait permettre d'accélérer considérablement les algorithmes de génération d'images dans le but de répondre aux besoins des futurs systèmes de thérapie assistée. Dans ce document, deux architectures optiques, correspondant aux deux opérations de base dans ce domaine, sont présentées : un système de filtrage et un système de rétroprojection. Ils sont abordés sous l'aspect matériel, puis sous l'aspect algorithmique. Quelle que soit la fonction réalisée, un processeur optique est toujours constitué de sources de lumière, d'afficheurs et de capteur d'images. L'état de l'art de ces composants révèle une faiblesse au niveau des afficheurs (SLM). En particulier, les SLM à base de cristaux liquides ferroélectriques sont étudiés en détail (modélisation, simulation et caractérisation de produits existants). L'intérêt des systèmes optiques de traitement est examiné à la fois du point de vue du temps de calcul, en comparaison avec les technologies numériques classiques, et en terme de qualité de traitement. Pour cela, les deux systèmes sont étudiés, dans un premier temps en simulation à l'aide d'un modèle approprié, puis expérimentalement sur un prototype. Dans le cadre du processeur de filtrage, les résultats restent plutôt moyens. Le rapport signal à bruit (SNR) sur les images reconstruites est de l'ordre de 20 dB en simulation avec un modèle dans lequel la majorité des distorsions géométriques n'ont pas été prises en compte. Les résultats expérimentaux mettent encore mieux en avant les limites de la méthode. Le travail de la lumière cohérente semble être un obstacle important. En revanche, les résultats avec le processeur de rétroprojection sont plutôt encourageants. Le modèle, beaucoup plus complet, et les simulations montrent qu'il est possible d'obtenir des images de qualité comparable à celles obtenues par calcul numérique (plus de 50 dB de SNR), avec une accélération d'un à deux ordres de grandeur. Les résultats obtenus avec le prototype expérimental confirment le potentiel de cette architecture. Une extension de ce travail concernant la réalisation d'un processeur hybride dédié à des algorithmes plus complexes (ex : l'algorithme ASSR pour la reconstruction d'image des CT-scan) est également présentée à la fin de ce document.