Low power circuits and systems for wireless neural stimulation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 155-161).Electrical stimulation of tissues is an increasingly valuable tool for treating a variety of disorders, with applications including cardiac pacemakers, cochlear implants, visual prostheses, deep brain stimulators, spinal cord stimulators, and muscle stimulators. Brain implants for paralysis treatments are increasingly providing sensory feedback via neural stimulation. Within the field of neuroscience, the perturbation of neuronal circuits wirelessly in untethered, freely-behaving animals is of particular importance. In implantable systems, power consumption is often the limiting factor in determining battery or power coil size, cost, and level of tissue heating, with stimulation circuitry typically dominating the power budget of the entire implant. Thus, there is strong motivation to improve the energy efficiency of implantable electrical stimulators. In this thesis, I present two examples of low-power tissue stimulators. The first type is a wireless, low-power neural stimulation system for use in freely behaving animals. The system consists of an external transmitter and a miniature, implantable wireless receiver-and-stimulator utilizing a custom integrated chip built in a standard 0.5 ptm CMOS process. Low power design permits 12 days of continuous experimentation from a 5 mAh battery, extended by an automatic sleep mode that reduces standby power consumption by 2.5x. To test this device, bipolar stimulating electrodes were implanted into the songbird motor nucleus HVC of zebra finches. Single-neuron recordings revealed that wireless stimulation of HVC led to a strong increase of spiking activity in its downstream target, the robust nucleus of the arcopallium (RA). When this device was used to deliver biphasic pulses of current randomly during singing, singing activity was prematurely terminated in all birds tested. The second stimulator I present is a novel, energy-efficient electrode stimulator with feedback current regulation. This stimulator uses inductive storage and recycling of energy based on a dynamic power supply to drive an electrode in an adiabatic fashion such that energy consumption is minimized. Since there are no explicit current sources or current limiters, wasteful energy dissipation across such elements is naturally avoided. The stimulator also utilizes a shunt current-sensor to monitor and regulate the current through the electrode via feedback, thus enabling flexible and safe stimulation. The dynamic power supply allows efficient transfer of energy both to and from the electrode, and is based on a DC-DC converter topology that is used in a bidirectional fashion. In an exemplary electrode implementation, I show how the stimulator combines the efficiency of voltage control and the safety and accuracy of current control in a single low-power integrated-circuit built in a standard 0.35 pm CMOS process. I also perform a theoretical analysis of the energy efficiency that is in accord with experimental measurements. In its current proof-of-concept implementation, this stimulator achieves a 2x-3x reduction in energy consumption as compared to a conventional current-source-based stimulator operating from a fixed power supply.by Scott Kenneth Arfin.Ph.D

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

A novel behavioural paradigm for characterising anticipatory postural adjustments in mice

Daily we use purposeful, voluntary movements to interact with our environment. These movements demand and cause our body to experience a weight redistribution, i.e., anticipatory postural adjustments (APAs), and it’s the appropriate employment of these APAs that allows us to complete said voluntary movements without falling over or losing our equilibrium. The literature suggests that for humans, monkeys, and several quadrupeds, APAs are crucial at initiation and during movement. However, research has been somewhat limited due to the lack of behavioural paradigms that would allow for a better understanding into the neural circuitry involved with APAs. Given the widespread availability of genetic tools and advanced viral techniques in mice I focused my efforts in developing a novel behavioral paradigm for this species. The first chapters detail the reasoning behind the development of this novel behavioural paradigm while also providing a complete description of the different components and their functions. Later chapters use the custom-designed setup to characterise mouse APAs, incorporating various recording approaches designed to quantify APAs and compare them to those described in prior work, highlighting possible interspecifies similarities and differences. Additionally, I briefly discuss the potential neural circuitry of APAs informed by my own data and research that has been done in different animals, providing a comprehensive overview of APAs in mice

Phase Synchronization Operator for On-Chip Brain Functional Connectivity Computation

This paper presents an integer-based digital processor for the calculation of phase synchronization between two neural signals. It is based on the measurement of time periods between two consecutive minima. The simplicity of the approach allows for the use of elementary digital blocks, such as registers, counters, and adders. The processor, fabricated in a 0.18- μ m CMOS process, only occupies 0.05 mm 2 and consumes 15 nW from a 0.5 V supply voltage at a signal input rate of 1024 S/s. These low-area and low-power features make the proposed processor a valuable computing element in closed-loop neural prosthesis for the treatment of neural disorders, such as epilepsy, or for assessing the patterns of correlated activity in neural assemblies through the evaluation of functional connectivity maps.Ministerio de Economía y Competitividad TEC2016-80923-POffice of Naval Research (USA) N00014-19-1-215

Integrated Circuits and Systems for Smart Sensory Applications

Connected intelligent sensing reshapes our society by empowering people with increasing new ways of mutual interactions. As integration technologies keep their scaling roadmap, the horizon of sensory applications is rapidly widening, thanks to myriad light-weight low-power or, in same cases even self-powered, smart devices with high-connectivity capabilities. CMOS integrated circuits technology is the best candidate to supply the required smartness and to pioneer these emerging sensory systems. As a result, new challenges are arising around the design of these integrated circuits and systems for sensory applications in terms of low-power edge computing, power management strategies, low-range wireless communications, integration with sensing devices. In this Special Issue recent advances in application-specific integrated circuits (ASIC) and systems for smart sensory applications in the following five emerging topics: (I) dedicated short-range communications transceivers; (II) digital smart sensors, (III) implantable neural interfaces, (IV) Power Management Strategies in wireless sensor nodes and (V) neuromorphic hardware

Modulation Techniques for Biomedical Implanted Devices and Their Challenges

Implanted medical devices are very important electronic devices because of their usefulness in monitoring and diagnosis, safety and comfort for patients. Since 1950s, remarkable efforts have been undertaken for the development of bio-medical implanted and wireless telemetry bio-devices. Issues such as design of suitable modulation methods, use of power and monitoring devices, transfer energy from external to internal parts with high efficiency and high data rates and low power consumption all play an important role in the development of implantable devices. This paper provides a comprehensive survey on various modulation and demodulation techniques such as amplitude shift keying (ASK), frequency shift keying (FSK) and phase shift keying (PSK) of the existing wireless implanted devices. The details of specifications, including carrier frequency, CMOS size, data rate, power consumption and supply, chip area and application of the various modulation schemes of the implanted devices are investigated and summarized in the tables along with the corresponding key references. Current challenges and problems of the typical modulation applications of these technologies are illustrated with a brief suggestions and discussion for the progress of implanted device research in the future. It is observed that the prime requisites for the good quality of the implanted devices and their reliability are the energy transformation, data rate, CMOS size, power consumption and operation frequency. This review will hopefully lead to increasing efforts towards the development of low powered, high efficient, high data rate and reliable implanted devices

Design, Fabrication, and Validation of a Highly Miniaturized Wirelessly Powered Neural Implant

We have recently witnessed an explosion in the number of neurons that can be recorded and/or stimulated simultaneously during neurophysiological experiments. Experiments have progressed from recording or stimulation with a single electrode to Micro-Electrode Array (MEA) such as the Utah Array. These MEAs can be instrumented with current drivers, neural amplifiers, digitizers and wireless communication links. The broad interest in these MEAs suggests that there is a need for large scale neural recording and stimulation. The ultimate goal is to coordinate the recordings and stimulation of potentially thousands of neurons from many brain areas. Unfortunately, current state-of-the-art MEAs are limited by their scalability and long-term stability because of their physical size and rigid configuration. Furthermore, some applications prioritize a distributed neural interface over one that offers high resolution. Examples of biomedical applications that necessitate an interface with neurons from many sites in the brain include: i) understanding and treating neurological disorders that affect distributed locations throughout the CNS; ii) revolutionizing our understanding of the brain by studying the correlations between neural networks from different regions of the brain and the mechanisms of cognitive functions; and iii) covering larger area in the sensorimotor cortex of amputees to more accurately control robotic prosthetic limbs or better evoke a sense of touch. One solution to make large scale, fully specifiable, electrical stimulation and recording possible, is to disconnect the electrodes from the base, so that they can be arbitrarily placed, using a syringe, freely in the nervous system. To overcome the challenges of system miniaturization, we propose the “microbead”, an ultra-small neural stimulating implant, that is currently implemented in a 130nm CMOS technology with the following characteristics: 200 μm × 200 μm × 80 μm size; optimized wireless powering, all micro-electronics on single chip; and integrated electrodes and coil. The stimulating microbead is validated in a sciatic nerve by generating leg movements. A recording microbead is also investigated with following characteristics: wireless powering using steerable phased coil array, miniaturized front-end, and backscattering telemetry. These microbeads could eventually replace the rigid arrays that are currently the state-of-the-art in electrophysiology set-ups

The microfluidic components of the freeform stimulator for neural modulation

Electronic devices can be interfaced with tissue via metal electrodes to deliver electrical current to stimulate target neurons for disease treatment. Different from the charge-balanced short pulse that can be safely applied in biology, direct current (DC) has been restricted from being applied for prolonged durations due to the toxicity generated by electrolysis around stimulation electrodes. On the other hand, as revealed by acute studies in animals, DC can be applied to suppress neural activity, a potential beneficial function for vestibular implants and devices intended to block pain signal in peripheral nerves or to treat epilepsy. To enable the use of prolonged DC in a human body, we developed a novel device we named Freeform Stimulator (FS). It is designed to safely deliver DC to neurons for arbitrary long durations without causing electrolysis. FS uses two pairs of electrodes to deliver charge-balanced currents into a microfluidic (µF) channel network. The induced ionic currents in the µF can be rectified into an ionic DC at the output of the device by the cyclical operation of two embedded valves that control the conduction of the channel network. FS could provide a way to safely apply prolonged DC in human body and benefit those applications that use DC to modulate neural activity. This thesis is focused on the development of the µF components that are required in the µF chip of FS which includes a shape memory alloy valve used to control ionic current, an ionic transistor that can be used as a non-mechanical control of ionic current and an ionic current sensor used to measure the ionic DC output. For proof of concept of FS, we tested the obtained µF chip with properly designed control of current and valve and succeeded in rectifying the ionic currents in µF into an ionic DC at the output

Aerospace Medicine and Biology. A continuing bibliography with indexes

This bibliography lists 244 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1981. Aerospace medicine and aerobiology topics are included. Listings for physiological factors, astronaut performance, control theory, artificial intelligence, and cybernetics are included