2 research outputs found

    Interfaces neuronales CMOS haute résolution pour l'électrophysiologie et l'optogénétique en boucle fermée

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    L’avenir de la recherche sur les maladies du cerveau repose sur le dĂ©veloppement de nouvelles technologies qui permettront de comprendre comment cet organe si complexe traite, intĂšgre et transfĂšre l’information. Parmi celles-ci, l’optogĂ©nĂ©tique est une technologie rĂ©volutionnaire qui permet d’utiliser de la lumiĂšre afin d’activer sĂ©lectivement les neurones du cortex d’animaux transgĂ©niques pour observer leur effet dans un vaste rĂ©seau biologique. Ce cadre expĂ©rimental repose typiquement sur l’observation de l’activitĂ© neuronale de souris transgĂ©niques, car elles peuvent exprimer une grande variĂ©tĂ© de gĂšnes et de maladies et qu’elles sont peu couteuses. Toutefois, la plupart des appareils de mesure ou de stimulation optogĂ©nĂ©tique disponible ne sont pas appropriĂ©s, car ils sont cĂąblĂ©s, trop lourds et/ou trop simplistes. Malheureusement, peu de systĂšmes sans fil existent, et ces derniers sont grandement limitĂ©s par la bande passante requise pour transmettre les donnĂ©es neuronales, et ils ne fournissent pas de stimulation optogĂ©nĂ©tique multicanal afin de stimuler et observer plusieurs rĂ©gions du cerveau. Dans les dispositifs actuels, l’interprĂ©tation des donnĂ©es neuronales est effectuĂ©e ex situ, alors que la recherche bĂ©nĂ©ficierait grandement de systĂšmes sans fil assez intelligents pour interprĂ©ter et stimuler les neurones en boucle fermĂ©e, in situ. Le but de ce projet de recherche est de concevoir des circuits analogiques-numĂ©riques d’acquisition et de traitement des signaux neuronaux, des algorithmes d’analyse et de traitement de ces signaux et des systĂšmes electro-optiques miniatures et sans fil pour : i) Mener des expĂ©riences combinant l’enregistrement neuronal et l’optogĂ©nĂ©tique multicanal haute rĂ©solution avec des animaux libres de leurs mouvements. ii) Mener des expĂ©riences optogĂ©nĂ©tiques synchronisĂ©es avec l’observation, c.-Ă -d. en boucle fermĂ©e, chez des animaux libres de leurs mouvements. iii) RĂ©duire la taille, le poids et la consommation Ă©nergĂ©tique des systĂšmes optogĂ©nĂ©tiques sans fil afin de minimiser l’impact de la recherche chez de petits animaux. Ce projet est en 3 phases, et ses principales contributions ont Ă©tĂ© rapportĂ©es dans dix confĂ©rences internationales (ISSCC, ISCAS, EMBC, etc.) et quatre articles de journaux publiĂ©s ou soumis, ainsi que dans un brevet et deux divulgations. La conception d’un systĂšme optogĂ©nĂ©tique haute rĂ©solution pose plusieurs dĂ©fis importants. Notamment, puisque les signaux neuronaux ont un contenu frĂ©quentiel Ă©levĂ© (_10 kHz), le nombre de canaux sous observation est limitĂ© par la bande passante des transmetteurs sans fil (2-4 canaux en gĂ©nĂ©ral). Ainsi, la premiĂšre phase du projet a visĂ© le dĂ©veloppement d’algorithmes de compression des signaux neuronaux et leur intĂ©gration dans un systĂšme optogĂ©nĂ©tique sans fil miniature et lĂ©ger (2.8 g) haute rĂ©solution possĂ©dant 32 canaux d’acquisition et 32 canaux de stimulation optique. Le systĂšme dĂ©tecte, compresse et transmet les formes d’onde des potentiels d’action (PA) produits par les neurones avec un field programmable gate array (FPGA) embarquĂ© Ă  faible consommation Ă©nergĂ©tique. Ce processeur implĂ©mente un algorithme de dĂ©tection des PAs basĂ© sur un seuillage adaptatif, ce qui permet de compresser les signaux en transmettant seulement les formes dĂ©tectĂ©es. Chaque PA est davantage compressĂ© par une transformĂ©e en ondelette discrĂšte (DWT) de type Symmlet-2 suivie d’une technique de discrimination et de requantification dynamique des coefficients. Les rĂ©sultats obtenus dĂ©montrent que cet algorithme est plus robuste que les mĂ©thodes existantes tout en permettant de reconstruire les signaux compressĂ©s avec une meilleure qualitĂ© (SNDR moyen de 25 dB _ 5% pour un taux de compression (CR) de 4.2). Avec la dĂ©tection, des CR supĂ©rieurs Ă  500 sont rapportĂ©s lors de la validation in vivo. L’utilisation de composantes commerciales dans des systĂšmes optogĂ©nĂ©tiques sans fil augmentela taille et la consommation Ă©nergĂ©tique, en plus de ne pas ĂȘtre optimisĂ©e pour cette application. La seconde phase du projet a permis de concevoir un systĂšme sur puce (SoC) complementary metal oxide semiconductor (CMOS) pour faire de l’enregistrement neuronal et de optogĂ©nĂ©tique multicanal, permettant de rĂ©duire significativement la taille et la consommation Ă©nergĂ©tique comparativement aux alternatives commerciales. Ceci est une contribution importante, car c’est la premiĂšre puce Ă  ĂȘtre dotĂ© de ces deux fonctionnalitĂ©s. Le SoC possĂšde 10 canaux d’enregistrement et 4 canaux de stimulation optogĂ©nĂ©tique. La conception du bioamplificateur inclut une bande passante programmable (0.5 Hz - 7 kHz) et un faible bruit referrĂ© Ă  l’entrĂ© (IRN de 3.2 ÎŒVrms), ce qui permet de cibler diffĂ©rents types de signaux biologiques (PA, LFP, etc.). Le convertisseur analogique numĂ©rique (ADC) de type Delta- Sigma (DS) MASH 1-1-1 est conçu pour fonctionner de faibles taux de sur-Ă©chantillonnage (OSR _50) pour rĂ©duire sa consommation et possĂšde une rĂ©solution programmable (ENOB de 9.75 Bits avec un OSR de 25). Cet ADC exploite une nouvelle technique rĂ©duisant la taille du circuit en soustrayant la sortie de chaque branche du DS dans le domaine numĂ©rique, comparativement Ă  la mĂ©thode analogique classique. La consommation totale d’un canal d’enregistrement est de 11.2 ÎŒW. Le SoC implĂ©mente un nouveau circuit de stimulation optique basĂ© sur une source de courant de type cascode avec rĂ©troaction, ce qui permet d’accommoder une large gamme de LED et de tensions de batterie comparativement aux circuits existants. Le SoC est intĂ©grĂ© dans un systĂšme optogĂ©nĂ©tique sans fil et validĂ© in vivo. À ce jour et en excluant ce projet, aucun systĂšme sans-fil ne fait de l’optogĂ©nĂ©tique en boucle fermĂ©e simultanĂ©ment au suivi temps rĂ©el de l’activitĂ© neuronale. Une contribution importante de ce travail est d’avoir dĂ©veloppĂ© le premier systĂšme optogĂ©nĂ©tique multicanal qui est capable de fonctionner en boucle fermĂ©e et le premier Ă  ĂȘtre validĂ© lors d’expĂ©riences in vivo impliquant des animaux libres de leurs mouvements. Pour ce faire, la troisiĂšme phase du projet a visĂ© la conception d’un SoC CMOS numĂ©rique, appelĂ© neural decoder integrated circuit (ND-IC). Le ND-IC et le SoC dĂ©veloppĂ© lors de la phase 2 ont Ă©tĂ© intĂ©grĂ©s dans un systĂšme optogĂ©nĂ©tique sans fil. Le ND-IC possĂšde 3 modules : 1) le dĂ©tecteur de PA adaptatif, 2) le module de compression possĂ©dant un nouvel arbre de tri pour discriminer les coefficients, et 3) le module de classement automatique des PA qui rĂ©utilise les donnĂ©es gĂ©nĂ©rĂ©es par le module de dĂ©tection et de compression pour rĂ©duire sa complexitĂ©. Un lien entre un canal d’enregistrement et un canal de stimulation est Ă©tabli selon l’association de chaque PA Ă  un neurone, grĂące Ă  la classification, et selon l’activitĂ© de ce neurone dans le temps. Le ND-IC consomme 56.9 ÎŒW et occupe 0.08 mm2 par canal. Le systĂšme pĂšse 1.05 g, occupe un volume de 1.12 cm3, possĂšde une autonomie de 3h, et est validĂ© in vivo.The future of brain research lies in the development of new technologies that will help understand how this complex organ processes, integrates and transfers information. Among these, optogenetics is a recent technology that allows the use of light to selectively activate neurons in the cortex of transgenic animals to observe their effect in a large biological network. This experimental setting is typically based on observing the neuronal activity of transgenic mice, as they express a wide variety of genes and diseases, while being inexpensive. However, most available neural recording or optogenetic devices are not suitable, because they are hard-wired, too heavy and/or too simplistic. Unfortunately, few wireless systems exist, and they are greatly limited by the required bandwidth to transmit neural data, while not providing simultaneous multi-channel neural recording and optogenetic, a must for stimulating and observing several areas of the brain. In current devices, the analysis of the neuronal data is performed ex situ, while the research would greatly benefit from wireless systems that are smart enough to interpret and stimulate the neurons in closed-loop, in situ. The goal of this project is to design analog-digital circuits for acquisition and processing of neural signals, algorithms for analysis and processing of these signals and miniature electrooptical wireless systems for: i) Conducting experiments combining high-resolution multi-channel neuronal recording and high-resolution multi-channel optogenetics with freely-moving animals. ii) Conduct optogenetic experiments synchronized with the neural recording, i.e. in closed loop, with freely-moving animals. iii) Increase the resolution while reducing the size, weight and energy consumption of the wireless optogenetic systems to minimize the impact of research with small animals. This project is in 3 phases, and its main contributions have been reported in ten conferences (ISSCC, ISCAS, EMBC, etc.) and four published journal papers, or submitted, as well as in a patent and two disclosures. The design of a high resolution optogenetic system poses several challenges. In particular, since the neuronal signals have a high frequency content (10 kHz), the number of chanv nels under observation is limited by the bandwidth of the wireless transmitters (2-4 channels in general). Thus, the first phase of the project focused on the development of neural signal compression algorithms and their integration into a high-resolution miniature and lightweight wireless optogenetics system (2.8g), having 32 recording channels and 32 optical stimulation channels. This system detects, compresses and transmits the waveforms of the signals produced by the neurons, i.e. action potentials (AP), in real time, via an embedded low-power field programmable gate array (FPGA). This processor implements an AP detector algorithm based on adaptive thresholding, which allows to compress the signals by transmitting only the detected waveforms. Each AP is further compressed by a Symmlet-2 discrete wavelet transform (DWT) followed dynamic discrimination and requantification of the DWT coefficients, making it possible to achieve high compression ratios with a good reconstruction quality. Results demonstrate that this algorithm is more robust than existing approach, while allowing to reconstruct the compressed signals with better quality (average SNDR of 25 dB 5% for a compression ratio (CR) of 4.2). With detection, CRs greater than 500 are reported during the in vivo validation. The use of commercial components in wireless optogenetic systems increases the size and power consumption, while not being optimized for this application. The second phase of the project consisted in designing a complementary metal oxide semiconductor (CMOS) system-on-chip (SoC) for neural recording and multi-channel optogenetics, which significantly reduces the size and energy consumption compared to commercial alternatives. This is important contribution, since it’s the first chip to integrate both features. This SoC has 10 recording channels and 4 optogenetic stimulation channels. The bioamplifier design includes a programmable bandwidth (0.5 Hz -7 kHz) and a low input-referred noise (IRN of 3.2 ÎŒVrms), which allows targeting different biological signals (AP, LFP, etc.). The Delta-Sigma (DS) MASH 1-1-1 low-power analog-to-digital converter (ADC) is designed to work with low OSR (50), as to reduce its power consumption, and has a programmable resolution (ENOB of 9.75 bits with an OSR of 25). This ADC uses a new technique to reduce its circuit size by subtracting the output of each DS branch in the digital domain, rather than in the analog domain, as done conventionally. A recording channel, including the bioamplifier, the DS and the decimation filter, consumes 11.2 ÎŒW. Optical stimulation is performed with an on-chip LED driver using a regulated cascode current source with feedback, which accommodates a wide range of LED parameters and battery voltages. The SoC is integrated into a wireless optogenetic platform and validated in vivo.To date and excluding this project, no wireless system is making closed-loop optogenetics simultaneously to real-time monitoring of neuronal activity. An important contribution of this work is to have developed the first multi-channel optogenetic system that is able to work in closed-loop, and the first to be validated during in vivo experiments involving freely-moving animals. To do so, the third phase of the project aimed to design a digital CMOS chip, called neural decoder integrated circuit (ND-IC). The ND-IC and the SoC developed in Phase 2 are integrated within a wireless optogenetic system. The ND-IC has 3 main cores: 1) the adaptive AP detector core, 2) the compression core with a new sorting tree for discriminating the DWT coefficients, and 3 ) the AP automatic classification core that reuses the data generated by the detection and compression cores to reduce its complexity. A link between a recording channel and a stimulation channel is established according to the association of each AP with a neuron, thanks to the classification, and according to the bursting activity of this neuron. The ND-IC consumes 56.9 ÎŒW and occupies 0.08 mm2 per channel. The system weighs 1.05 g, occupies a volume of 1.12 cm3, has an autonomy of 3h, and is validated in vivo

    A Novel Structure of Low-Order High Resolution Delta-Sigma Modulator

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    PƙeklĂĄdanĂĄ dizertačnĂ­ prĂĄce se zabĂœvĂĄ novou strukturou modulĂĄtoru delta-sigma (), kterĂĄ potlačuje vlivy vyĆĄĆĄĂ­ch harmonickĂœch sloĆŸek a umoĆŸĆˆuje dosĂĄhnout vysokĂ©ho rozliĆĄenĂ­ aĆŸ 16 bitĆŻ. NovĂĄ navrĆŸenĂĄ struktura kombinuje vĂœhody struktur modulĂĄtorĆŻ s jednobitovĂœm kvantizĂĄtorem s modulĂĄtory s vĂ­cebitovĂœm kvantizĂĄtorem. V prĂĄci je pƙedstavena novĂĄ struktura 2. ƙádu, byla ověƙena jejĂ­ sprĂĄvnĂĄ funkce v programu MATLAB a vyhodnoceny nĂĄroky na jednotlivĂ© bloky pƙevodnĂ­ku . DruhĂĄ část prĂĄce se zabĂœvĂĄ nĂĄvrhem pƙevodnĂ­ku s novou strukturou modulĂĄtoru v technologii ONSemi I3T25 s vyuĆŸitĂ­m techniky SC. Na zĂĄkladě poznatkĆŻ jsou na zĂĄvěr vyhodnoceny vĂœhody a nevĂœhody novĂ© struktury a je porovnĂĄna se znĂĄmĂœmi strukturami modulĂĄtorĆŻ .The presented dissertation thesis deals with a novel structure of delta-sigma () modulator which compensates influence of higher harmonic distortion and therefore it is possible to achieve high resolution up to 16 bits. This novel proposed structure combines advantages of one bit quantizer modulators with mutli-bit modulators. The novel second order structure is presented, correct function is verified in MATLAB simulation enviroment and requirements for partial block are studied. The second part of the work deals with design of converter with novel structure of modulator using switched capacitor technique utilizing ONSemi I3T25 technology. Advantages and disadvantages of the novel structure are evaluated and novel structure is compared with common structures of modulators.
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