A power efficient time-to-current stimulator for vagal-cardiac connection after heart transplantation

This paper presents a stimulator for a cardiac neuroprosthesis aiming to restore the parasympathetic control after heart transplantation. The stimulator is based on time-to-current conversion, instead of the conventional current mode digital-to-analog converter (DAC) that drives the output current mirrors. It uses a DAC based on capacitor charging to drive a power efficient voltage-to-current converter for output. The stimulator uses 1.8 V for system operation and 10 V for stimulation. The total power consumption is Istim × 10 V +18. u μW during the biphasic current output, with a maximum Istim of 512 μA. The stimulator was designed in CMOS 0.18 μm technology and post-layout simulations are presented

A Multi-Channel Stimulator With High-Resolution Time-to-Current Conversion for Vagal-Cardiac Neuromodulation

This paper presents an integrated stimulator for a cardiac neuroprosthesis aiming to restore the parasympathetic control after heart transplantation. The stimulator is based on time-to-current conversion. Instead of the conventional current mode digital-to-analog converter (DAC) that uses ten of microamp for biasing, the proposed design uses a novel capacitor time-based DAC offering close to 10 bit of current amplitude resolution while using only a bias current 250 nA. The stimulator chip was design in a 0.18 m CMOS high-voltage (HV) technology. It consists of 16 independent channels, each capable of delivering 550 A stimulus current under a HV output stage that can be operated up to 30 V. Featuring both power efficiency and high-resolution current amplitude stimulation, the design is suitable for multi-channel neural simulation applications

Desenvolvimento de um protótipo de neuroestimulador para dor crônica

Monografia (graduação)—Universidade de Brasília, Faculdade UnB Gama, Curso de Engenharia Eletrônica, 2015.Este trabalho apresenta o desenvolvimento de um protótipo de Estimulador Medular Espinhal direcionado ao tratamento de dor crônica. Um sistema de Estimulação Medular Espinhal é normalmente composto por um transmissor telemétrico e um circuito estimulador implantável, também conhecido como Gerador de Pulso Implantável (IPG). O transmissor atua como um programador externo, enviando os parâmetros de estimulação tais como amplitude do sinal, frequência, largura de pulso e forma de onda de estimulação para um circuito modulador. O circuito estimulador aplica então os pulsos de acordo com a configuração dos parâmetros diretamente no espaço epidural da medula espinhal com a ajuda de eletrodos implantados cirurgicamente na região mencionada. Nós apresentamos, primeiramente, os fundamentos teóricos por trás da estimulação da medula espinhal. Depois, mostramos os métodos utilizados para a construção de nossa arquitetura e para a seleção de hardware realizada, com uma com cada seção detalhada ponto a ponto. Finalmente, apresentamos os procedimentos experimentais realizados em nosso laboratório e os resultados obtidos, e mostramos também o método de análise sobre estes, além de uma discussão sobre futuras arquiteturas e hardwares que venhamos a desenvolver. ______________________________________________________________________________ ABSTRACTThis paper presents the development of a Spinal Cord Stimulator (SCS) prototype targeted to the treatment of chronic pain. A SCS system is usually comprised of a telemetric transmitter and a implantable stimulation circuit, also referred as implantable pulse generator (IPG). The transmitter acts as an external programmer, sending stimulation parameters such as signal amplitude, frequency, pulse-width and type of waveform to a modulator circuit. The stimulation circuit then applies pulses according to the specified parameters directly into the epidural space of the spinal cord with the help of electrode leads surgically implanted in the mentioned region. We first present a theoretical background on the subject of spinal cord stimulation. Then we present the methods behind our architecture and hardware selection, with a detailed view on each section. Experimental procedures done in our laboratory are also presented as well as our methods of analysis. Finally we analyze the accuracy of our prototype in comparison to commercially available SCS systems and discuss about future hardware and system architecture changes

Fully-Implantable Self-Contained Dual-Channel Electrical Recording and Directivity-Enhanced Optical Stimulation System on a Chip

This thesis presents an integrated system-on-a-chip (SoC), designed, fabricated, and characterized for conducting simultaneous dual-channel optogenetic stimulation and electrophysiological recording. An inductive coil as well as power management circuits are also integrated on the chip, enabling wireless power reception, hence, allowing full implantation. The optical stimulation channels host a novel LED driver circuit that can generate currents up to 10mA with a minimum required headroom voltage reported in the literature, resulting in a superior power efficiency compared to the state of the art. The output current in each channel can be programmed to have an arbitrary waveform with digitally-controlled magnitude and timing. The final design is fabricated as a 34 mm2 microchip using a CMOS 130nm technology and characterized both in terms of electrical and optical performance. A pair of custom-designed inkjet-printed micro-lenses are also fabricated and placed on top of the LEDs. The lenses are optimized to enhance the light directivity of optical stimulation, resulting in significant improvements in terms of spatial resolution, power consumption (30.5x reduction), and safety aspects (temperature increase of <0.1c) of the device

Génération de stimuli efficaces en énergie pour la microstimulation électrique intracorticale

RÉSUMÉ Ce mémoire a comme objectif principal la mise en oeuvre de circuits dédiés à l’amélioration de l’efficacité de la stimulation électrique de tissus situés au niveau du cortex visuel primaire. Le stimulateur proposé permet la génération de nouveaux stimuli flexibles de forme exponentielle et demi-sinusoïdale dans l’optique de réduire la consommation de puissance globale de l’implant. En plus d’être potentiellement plus efficaces que les stimulations rectangulaires standard pour exciter les tissus, ces formes d’impulsions permettraient également de réduire la concentration d’ions toxiques relâchés par les électrodes. Le second objectif de ce projet est de permettre la stimulation à pleine échelle, soit au moins 150 µA, à travers l’interface microélectrode-tissus qui est caractérisée par une impédance élevée. Un étage de sortie à haute-tension a donc également été réalisé afin de générer des tensions d’alimentation d’environ ±9 V et d’augmenter ainsi l’excursion de tension des stimuli tout en étant entièrement intégré. Une architecture comportant deux circuits intégrés indépendants est proposée dans ce mémoire. Le générateur de stimuli est implémenté dans la technologie CMOS 0,18-µ m 1,8V/3,3V de TSMC afin de limiter sa consommation de puissance. Pour ce qui est de l’étage de sortie, il est intégré à l’aide du procédé C08E CMOS/DMOS 0,8-µ m 5V/20V de DALSA Semiconductors, technologie supportant les niveaux de tension requis.Les deux puces ainsi fabriquées ont été testées. L’intensité des stimuli rectangulaires couvre une plage de 1,6 à 167,2 µ A des erreurs de non-linéarité différentielle et intégrale de 0,10 et 0,16 LSB respectivement. Les impulsions exponentielles ont une plage dynamique de 34,36 dB pour une erreur de ±0,5 dB par rapport à la fonction théorique. La consommation de puissance du générateur de stimuli atteint en moyenne 29,1 µW en mode rectangulaire et de 28,5 à 88,3 µ W en mode exponentiel. Les résultats obtenus pour la demi-sinusoïde proviennent de simulations. En moyenne, 80,2 % de la durée des impulsions demi-sinusoïdales a une erreur inférieure à ±1 % par rapport à la fonction idéale. Le générateur de stimuli complet consomme de 46,7 à 199,1 µW en mode demi-sinusoïdal. En ce qui a trait à l’étage de sortie, des tensions de 8,95 et -8,46 V sont générées avec succès, permettant à l’excursion de tension d’atteindre 13,6 V à travers une charge de 100 kΩ.----------ABSTRACT This master thesis’ main objective is the implementation of circuits dedicated to electrical stimulation efficiency enhancement for tissues in the primary visual cortex. The proposed stimulator allows novel stimuli waveform generation such as flexible exponential and half-sine pulses in order to reduce the implant’s global power consumption. In addition of being potentially more efficient to excite neural tissues than standard rectangular pulse-based stimulations, these waveforms should also reduce toxic ions concentration released by the electrodes. Moreover, this project’s second objective is to allow full-scale stimulation, i.e., at least 150 µA, through high-impedance microelectrode-tissue interfaces. A high-voltage output stage has also been realized to generate ±9 V voltage supplies to increase the voltage swing while being fully-integrated. An architecture composed of two independent integrated circuits has been proposed. The stimuli generator is implemented in TSMC CMOS 0.18-µ m 1.8V/3.3V technology to limit its power consumption. On the other hand, the output stage is integrated in C08E CMOS/DMOS 0.8- µm 5V/20V process from DALSA Semiconductors as this technology supports the required voltage levels.These two fabricated chips were tested. Rectangular stimuli intensity varies from 1.6 to 167.2 µA with differential and integral nonlinearities of 0.10 and 0.16 LSB, respectively. Exponential pulses show a dynamic range of 34.36 dB for an error of ±0.5 dB with the theoretical waveform. The stimuli generator’s power consumption reaches an average of 29.1 µW in rectangular mode and from 28.5 to 88.3 µW in exponential mode. Half-sine results are obtained from simulations. An average of 80.2 % of half-sine pulse duration has an error lower than ±1 % with the ideal sine function. The whole stimuli generator consumes from 46.7 to 199.1 µW in half-sine mode. For the output stage, voltages of 8.95 and -8.46 V are successfully generated, allowing the output voltage compliance to reach 13.6 V through a 100 kΩ load. However, this chip dissipates 51.37 mW when operating normally

Design of a Quasi-Adiabatic Current-Mode Neurostimulator Integrated Circuit for Deep Brain Stimulation

Electrical stimulation of neural tissues is a valuable tool in the retinal prosthesis, cardiac pacemakers, and Deep Brain Stimulation (DBS). DBS is being to treat a growing number of neurological disorders, such as movement disorder, epilepsy, and Parkinson’s disease. The role of the electronic stimulator is paramount in such application, and significant design challenges are to be met to enhance safety and reliability. A current-source based stimulator can accurately deliver a charge-balanced stimulus maintaining patient safety. In this thesis, a general-purpose current-mode neurostimulator (CMS) based upon a new quasi-adiabatic driving technique is proposed which can theoretically achieve more than 80% efficiency with the help of a dynamic high voltage supply (DHVS) as opposed to most conventional general-purpose CMS having less than 25% efficiency. The high-voltage supply is required to withstand the voltage seen across the electrodes (>10V) due to the time-varying impedance presented by the electrode-tissue interface. The overall efficiency of the designed CMS is limited by the efficiency of the DHVS. A HVDD of 15V is created by the DHVS from an input voltage (VDD) of 3V. The DHVS circuit is made by cascading five charge pump circuits using the AMI 0.5µm CMOS process. It can maintain more than 60% efficiency for a wide range of load current from 25µA to 1.4mA, with peak efficiency at 67% and this is comparable with existing specific-purpose state-of-the-art high-voltage supplies used in a current stimulator. The stimulator designed in this thesis employs a new efficient charge recycling mechanism to enhance the overall efficiency, compared to the existing state-of-the-art CMSs. Thus, the overall CMS efficiency is improved by 20% to 25%. A current source, programmable by 8-bit digital input, is also designed which has an output impedance greater than 2MΩ with a dropout voltage of only 120mV. Measurements show voltage compliance exceeding +/-15V when driving a biphasic current stimulus of 10µA to 2.5mA through a simplified R-C model of the electrode-tissue interface. The voltage compliance is defined as the maximum voltage a stimulator can apply across the electrodes to achieve neural stimulation

광 다이오드 기반 인공 망막 시스템을 위한 저전력 설계 및 LCP 패키징에 대한 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 김성준.The retinal prosthesis is an implantable electronic device that delivers electrical stimuli containing visual information to the retina for the visual restoration of the blinds. The currently available retinal prostheses have several problems in the number of pixels. They are limited in the number of pixels, which restricts the amount of visual information they can deliver. Many research groups are trying to improve their device in this aspect. In order to achieve a significant number of pixels, retinal prosthesis needs large stimulus power dissipation. A typical device consumes more than 20 mW of power to drive 1000 channels. Some of this power can lead to temperature rise which is a safety issue. As the power dissipation scales up with the increase in the number of channels, it is desired to minimize the power per channel as much as possible. Another problem is the absence of a suitable packaging material for the long-term reliable optical window. Due to the curved and narrow implant space available for this kind of device, as well as the transparency required for the incoming wavelengths of lights, it is quite difficult to choose a material that satisfies all requirements of long-term hermetic packaging with optically transparent window. Sapphire glass with titanium metal package are too bulky and rigid, and flexible transparent polymers such as polyimide and parylene-C have high moisture absorption for the implant. This dissertation proposes strategies and methods to solve the problems mentioned above. Two stimulation strategies are proposed. One strategy is to confine the stimulus level with a threshold that cell is activated. Thus we coin it as thresholding strategy.' The other strategy is to reduce the number of stimulation channels by using only outlines of images (outline extraction strategy). Prototype ICs were designed and fabricated for the verification of the effects of these strategies. The simulation and the measurement agree to show that retinal implant with the thresholding and outline extraction strategies consumes below one-third of the stimulus power of the conventional photodiode-based devices. Area-efficient designs of the voltage-controlled current source are also adopted to increase the number of channels. The unit pixel area of the fabricated prototype IC was 0.0072 mm2, expanding up to 1200-channels in the macular area. Liquid crystal polymer (LCP) is proposed as the long-term implantable packaging material with an optical window. It is an inert, biocompatible, and flexible polymer material that has a moisture absorption rate similar to Pyrex glass. We showed that an LCP film with a thickness less than 10 μm allows transmission of the lights in the visible wavelengths by more than 10 %, as the rate increases with thinner films. Thus a thinning process was developed. O2 DRIE was shown effective in reducing the roughness of the film, and the corresponding light scattering. The spatial resolution of LCP with 8.28 μm thickness showed a minimum distinguishable pitch of 90 μm, allowing a 1200 channel integration within a macular area.Chapter 1: Introduction 1 1.1. Retinal Prosthesis – State of the Arts 2 1.1.1. Retinal Prosthesis with External Camera 3 1.1.2. Retinal Prosthesis with Internal Photodiode Array 5 1.2. Photodiode-based Retinal Prosthesis 8 1.2.1. Problems 8 1.2.2. Possible Solutions 12 Chapter 2: Methods 17 2.1. Thresholding 17 2.1.1. Concept 17 2.1.2. Circuit Descriptions 19 2.2. Outline Extraction 28 2.2.1. Concept 28 2.2.2. Circuit Descriptions 30 2.3. Average Stimulus Power Estimation 40 2.3.1. Stimulus Patterns Generation of Conventional and Proposed Strategies 40 2.3.2. Minimum Distinguishable Channels to Recognize 41 2.4. Virtual Channel 43 2.4.1. Concept 43 2.4.2. Circuit Descriptions 44 2.5. Polymer Packaging 51 2.5.1. LCP as a Long-term Reliable Packaging Material 51 2.5.2. Test Methods 53 Chapter 3: Results 58 3.1. Thresholding 58 3.1.1. Fabricated IC 58 3.1.2. Test Setup 60 3.1.3. Test Results 61 3.2. Outline Extraction 65 3.2.1. Simulation Results 65 3.2.2. Fabricated IC 67 3.2.3. Test Setup 68 3.2.4. Test Results 72 3.3. Average Stimulus Power Estimation 76 3.4. Virtual Channels 79 3.4.1. Fabricated IC 79 3.4.2. Test Setup 80 3.4.3. Test Results 81 3.4.4. Two-dimensional Virtual Channel Generator– Test setup and Its Result 84 3.5. Polymer Packaging 87 3.5.1. Light Transmittance according to LCP Thickness 87 3.5.2. Thickness Control of LCP 89 3.5.3. Spatial Resolution of LCP 89 Chapter 4: Discussion 92 4.1. Average Stimulus Power 92 4.2. Visual Acuity 95 4.3. Hermeticity of the Thinned LCP Film 97 Chapter 5: Conclusion and Future Directions 99 References 103 Appendix – Generated Stimulus Patterns of Various the Number of Channels 112 국 문 초 록 139Docto

Charge Pumps for Implantable Microstimulators in Low and High-Voltage Technologies

RÉSUMÉ L'objectif principal de cette thèse est de concevoir et mettre en œuvre une pompe de charge qui peut produire suffisamment de tension afin de l’implémenter à un système de prothèse visuelle, conçue par le laboratoire PolyStim neurotechnologies. Il a été constaté que l'une des parties les plus consommatrices d'énergie de l'ensemble du système de prothèse visuelle est la pompe de charge. En raison de la nature variable du tissu nerveux et de l'interface d’électrode, la tension nécessaire par stimuler le tissu nerveux est très élevé et consomme extrêmement d’énergie. En outre, afin de fournir du courant biphasique aux électrodes il faut produire des tensions positives et négatives. La génération de tension négative est très difficile, surtout dans les technologies à faible tension compte tenu des limites de la technologie. Le premier objectif du projet est de générer la haute tension nécessaire qui va consommer une faible puissance statique. La technologie de haute tension a été utilisée dans le but d’atteindre cet objectif. Le deuxième objectif est de générer la tension requise dans la technologie de basse tension et ainsi surmonter les limites de la technologie. Dans les deux cas, une attention particulière a été portée afin que personne ne latch-up apparaît pour le cycle négatif. L'architecture de la conception proposée a été présentée dans cette thèse. La pompe de charge a été conçu et mis en oeuvre à la fois dans la technologie CMOS 0,8 μm offert par TELEDYNE DALSA et technologie 0,13 μm CMOS offert par IBM. En raison de la tension requise, 0,8 μm technologie a été utilisée pour atteindre la sortie et conçu pour minimiser la consommation de puissance statique. La même architecture a été mise en oeuvre en technologie 0,13 μm pour enquêter sur la tension de sortie obtenue avec une faible consommation électrique. Les deux puces ont été testées en laboratoire PolyStim. Les résultats testés ont montré une variation moyenne très faible de déviation inférieure à 5% par rapport au résultat de simulation. Pour la conception en 0,8 µm, nous avons été en mesure d'obtenir plus de 25 V avec une consommation électrique très faible d’énergie statique de 3,846 mW et une charge d'entraînement maximum de 2 mA avec un maximum d'efficacité de 84,2%. Pour le même processus en 0,13 µm, les resultats ont été plus que 20V, 0,913 mW, 500 µA, et 85,2% respectivement.----------ABSTRACT The main objective of the thesis is to design and implement a charge pump that can produce enough voltage required to be implemented to the visual prosthesis system, designed by the PolyStim Neurotechnologies laboratory. It has been found that one of the most power consuming parts of the whole visual prosthesis system is the charge pump. Due to the variable nature of the nerve tissue and electrode interface, the required voltage of stimulating the nerve tissue is very high and thus extremely power consuming. Also, in order to provide biphasic current to the electrodes, there is a requirement of generating both positive and negative voltages. Generating negative voltage is very hard especially in low voltage technologies considering the technology limitations. The first objective of the project is to generate required high voltage that will consume low static power. High voltage technology has been used to achieve the goal. The second objective is to generate the required voltage in low voltage technology overcoming the technology limitations. In both cases, special care has been taken so that no latch-up occurs for the negative cycle. Architecture of the proposed design has been presented in this thesis. The charge pump has been designed and implemented in both 0.8 µm CMOS technology offered by TELEDYNE DALSA and 0.13 µm CMOS technology offered by IBM. Because of the required voltage, 0.8 µm technology has been used to achieve the output and designed to minimize the static power consumption. The same architecture has been implemented in 0.13 µm technology to investigate the achievable output voltage with low power consumption. Both the chips have been tested in polyStim laboratory. The tested results have shown very low variation of less than 5% average deflection from the simulation output. For the design in 0.8 µm, we have been able to get more than 25 V output with very low static power consumption of 3.846 mW and maximum drive load of 2 mA with maximum efficiency of 84.2%. For the same design in 0.13 µm, the outputs were more than 20V, 0.913 mW, 500 µA, and 85.2% respectively

Wireless Simultaneous Stimulation-and-Recording Device (SRD) to Train Cortical Circuits in Rat Somatosensory Cortex

The primary goal of this project is to develop a wireless system for simultaneous recording-and-stimulation (SRD) to deliver low amplitude current pulses to the primary somatosensory cortex (SI) of rats to activate and enhance an interhemispheric cortical pathway. Despite the existence of an interhemispheric connection between similar forelimb representations of SI cortices, forelimb cortical neurons respond only to input from the contralateral (opposite side) forelimb and not to input from the ipsilateral (same side) forelimb. Given the existence of this interhemispheric pathway we have been able to strengthen/enhance the pathway through chronic intracortical microstimulation (ICMS) in previous acute experiments of anesthetized rats. In these acute experiments strengthening the interhemispheric pathway also brings about functional reorganization whereby cortical neurons in forelimb cortex respond to new input from the ipsilateral forelimb. Having the ability to modify cortical circuitry will have important applications in stroke patients and could serve to rescue and/or enhance responsiveness in surviving cells around the stroke region. Also, the ability to induce functional reorganization within the deafferented cortical map, which follows limb amputation, will also provide a vehicle for modulating maladaptive cortical reorganization often associated with phantom limb pain leading to reduced pain. In order to increase our understanding of the observed functional reorganization and enhanced pathway, we need to be able to test these observations in awake and behaving animals and eventually study how these changes persist over a prolonged period of time. To accomplish this a system was needed to allow simultaneous recording and stimulation in awake rats. However, no such commercial or research system exists that meets all requirements for such an experiment. In this project we describe the (1) system design, (2) system testing, (3) system evaluation, and (4) system implementation of a wireless simultaneous stimulation-and-recording device (SRD) to be used to modulate cortical circuits in an awake rodent animal model