Inductively Coupled CMOS Power Receiver For Embedded Microsensors

Inductively coupled power transfer can extend the lifetime of embedded microsensors that save costs, energy, and lives. To expand the microsensors' functionality, the transferred power needs to be maximized. Plus, the power receiver needs to handle wide coupling variations in real applications. Therefore, the objective of this research is to design a power receiver that outputs the highest power for the widest coupling range. This research proposes a switched resonant half-bridge power stage that adjusts both energy transfer frequency and duration so the output power is maximally high. A maximum power point (MPP) theory is also developed to predict the optimal settings of the power stage with 98.6% accuracy. Finally, this research addresses the system integration challenges such as synchronization and over-voltage protection. The fabricated self-synchronized prototype outputs up to 89% of the available power across 0.067%~7.9% coupling range. The output power (in percentage of available power) and coupling range are 1.3× and 13× higher than the comparable state of the arts.Ph.D

Wireless Power Transfer Techniques for Implantable Medical Devices:A Review

Wireless power transfer (WPT) systems have become increasingly suitable solutions for the electrical powering of advanced multifunctional micro-electronic devices such as those found in current biomedical implants. The design and implementation of high power transfer efficiency WPT systems are, however, challenging. The size of the WPT system, the separation distance between the outside environment and location of the implanted medical device inside the body, the operating frequency and tissue safety due to power dissipation are key parameters to consider in the design of WPT systems. This article provides a systematic review of the wide range of WPT systems that have been investigated over the last two decades to improve overall system performance. The various strategies implemented to transfer wireless power in implantable medical devices (IMDs) were reviewed, which includes capacitive coupling, inductive coupling, magnetic resonance coupling and, more recently, acoustic and optical powering methods. The strengths and limitations of all these techniques are benchmarked against each other and particular emphasis is placed on comparing the implanted receiver size, the WPT distance, power transfer efficiency and tissue safety presented by the resulting systems. Necessary improvements and trends of each WPT techniques are also indicated per specific IMD

Communication and energy delivery architectures for personal medical devices

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 219-232).Advances in sensor technologies and integrated electronics are revolutionizing how humans access and receive healthcare. However, many envisioned wearable or implantable systems are not deployable in practice due to high energy consumption and anatomically-limited size constraints, necessitating large form-factors for external devices, or eventual surgical re-implantation procedures for in-vivo applications. Since communication and energy-management sub-systems often dominate the power budgets of personal biomedical devices, this thesis explores alternative usecases, system architectures, and circuit solutions to reduce their energy burden. For wearable applications, a system-on-chip is designed that both communicates and delivers power over an eTextiles network. The transmitter and receiver front-ends are at least an order of magnitude more efficient than conventional body-area networks. For implantable applications, two separate systems are proposed that avoid reimplantation requirements. The first system extracts energy from the endocochlear potential, an electrochemical gradient found naturally within the inner-ear of mammals, in order to power a wireless sensor. Since extractable energy levels are limited, novel sensing, communication, and energy management solutions are proposed that leverage duty-cycling to achieve enabling power consumptions that are at least an order of magnitude lower than previous work. Clinical measurements show the first system demonstrated to sustain itself with a mammalian-generated electrochemical potential operating as the only source of energy into the system. The second system leverages the essentially unlimited number of re-charge cycles offered by ultracapacitors. To ease patient usability, a rapid wireless capacitor charging architecture is proposed that employs a multi-tapped secondary inductive coil to provide charging times that are significantly faster than conventional approaches.by Patrick Philip Mercier.Ph.D

Design of Wireless Power Transfer and Data Telemetry System for Biomedical Applications

With the advancement of biomedical instrumentation technologies sensor based remote healthcare monitoring system is gaining more attention day by day. In this system wearable and implantable sensors are placed outside or inside of the human body. Certain sensors are needed to be placed inside the human body to acquire the information on the vital physiological phenomena such as glucose, lactate, pH, oxygen, etc. These implantable sensors have associated circuits for sensor signal processing and data transmission. Powering the circuit is always a crucial design issue. Batteries cannot be used in implantable sensors which can come in contact with the blood resulting in serious health risks. An alternate approach is to supply power wirelessly for tether-less and battery- less operation of the circuits.Inductive power transfer is the most common method of wireless power transfer to the implantable sensors. For good inductive coupling, the inductors should have high inductance and high quality factor. But the physical dimensions of the implanted inductors cannot be large due to a number of biomedical constraints. Therefore, there is a need for small sized and high inductance, high quality factor inductors for implantable sensor applications. In this work, design of a multi-spiral solenoidal printed circuit board (PCB) inductor for biomedical application is presented. The targeted frequency for power transfer is 13.56 MHz which is within the license-free industrial, scientific and medical (ISM) band. A figure of merit based optimization technique has been utilized to optimize the PCB inductors. Similar principal is applied to design on-chip inductor which could be a potential solution for further miniaturization of the implantable system. For layered human tissue the optimum frequency of power transfer is 1 GHz for smaller coil size. For this reason, design and optimization of multi-spiral solenoidal integrated inductors for 1 GHz frequency is proposed. Finally, it is demonstrated that the proposed inductors exhibit a better overall performance in comparison with the conventional inductors for biomedical applications

A Critical Analysis of a Wireless Power Transmission (WPT) with an Improvement Method for a Non-Radiative WPT

This paper describes the analysis of the wireless power transmission including recent progresses in non-radiative wireless power transmission (WPT) and the improvement methods. Generally, WPT transmitter side consists of a DC supply voltage source, inverter/power amplifier, transmitter impedance matching device (IMD), source resonator and primary coil. The WPT receiver meanwhile consists of the secondary coil, device resonator, receiver IMD, rectifier and load. In order to achieve an efficient WPT, the WPT transmitter must transmit energy with minimum loss at the receiver side.  This setup can be achieved by employing the power amplifier (PA). In this paper, the power amplifier in wireless power transmission for portable devices was designed. A Class E power amplifier was proposed and designed to improve the WPT transmitter side. The effects of zero voltage and zero derivative voltage switching on PA with optimization method was also discussed

Design of Power Management Integrated Circuits and High-Performance ADCs

A battery-powered system has widely expanded its applications to implantable medical devices (IMDs) and portable electronic devices. Since portable devices or IMDs operate in the energy-constrained environment, their low-power operations in combination with efficiently sourcing energy to them are key problems to extend device life. This research proposes novel circuit techniques for two essential functions of a power receiving unit (PRU) in the energy-constrained environment, which are power management and signal processing. The first part of this dissertation discusses power management integrated circuits for a PRU. From a power management perspective, the most critical two circuit blocks are a front-end rectifier and a battery charger. The front-end CMOS active rectifier converts transmitted AC power into DC power. High power conversion efficiency (PCE) is required to reduce power loss during the power transfer, and high voltage conversion ratio (VCR) is required for the rectifier to enable low-voltage operations. The proposed 13.56-MHz CMOS active rectifier presents low-power circuit techniques for comparators and controllers to reduce increasing power loss of an active diode with offset/delay calibration. It is implemented with 5-V devices of a 0.35 µm CMOS process to support high voltage. A peak PCE of 89.0%, a peak VCR of 90.1%, and a maximum output power of 126.7 mW are measured for 200Ω loading. The linear battery charger stores the converted DC power into a battery. Since even small power saving can be enough to run the low-power PRU, a battery charger with low IvQ is desirable. The presented battery charger is based on a single amplifier for regulation and the charging phase transition from the constant-current (CC) phase to the constant-voltage (CV) phase. The proposed unified amplifier is based on stacked differential pairs which share the bias current. Its current-steering property removes multiple amplifiers for regulation and the CC-CV transition, and achieves high unity-gain loop bandwidth for fast regulation. The charger with the maximum charging current of 25 mA is implemented in 0.35 µm CMOS. A peak charger efficiency of 94% and average charger efficiency of 88% are achieved with an 80-mAh Li-ion polymer battery. The second part of this dissertation focuses on analog-to-digital converters (ADCs). From a signal processing perspective, an ADC is one of the most important circuit blocks in the PRU. Hence, an energy-efficient ADC is essential in the energy-constrained environment. A pipelined successive approximation register (SAR) ADC has good energy efficiency in a design space of moderate-to-high speeds and resolutions. Process-Voltage-Temperature variations of a dynamic amplifier in the pipelined-SAR ADC is a key design issue. This research presents two dynamic amplifier architectures for temperature compensation. One is based on a voltage-to-time converter (VTC) and a time-to-voltage converter (TVC), and the other is based on a temperature-dependent common-mode detector. The former amplifier is adopted in a 13-bit 10-50 MS/s subranging pipelined-SAR ADC fabricated in 0.13-µm CMOS. The ADC can operate under the power supply voltage of 0.8-1.2 V. Figure-of-Merits (FoMs) of 4-11.3 fJ/conversion-step are achieved. The latter amplifier is also implemented in 0.13-µm CMOS, consuming 0.11 mW at 50 MS/s. Its measured gain variation is 2.1% across the temperature range of -20°C to 85 °C

A Three – tier bio-implantable sensor monitoring and communications platform

One major hindrance to the advent of novel bio-implantable sensor technologies is the need for a reliable power source and data communications platform capable of continuously, remotely, and wirelessly monitoring deeply implantable biomedical devices. This research proposes the feasibility and potential of combining well established, ‘human-friendly' inductive and ultrasonic technologies to produce a proof-of-concept, generic, multi-tier power transfer and data communication platform suitable for low-power, periodically-activated implantable analogue bio-sensors. In the inductive sub-system presented, 5 W of power is transferred across a 10 mm gap between a single pair of 39 mm (primary) and 33 mm (secondary) circular printed spiral coils (PSCs). These are printed using an 8000 dpi resolution photoplotter and fabricated on PCB by wet-etching, to the maximum permissible density. Our ultrasonic sub-system, consisting of a single pair of Pz21 (transmitter) and Pz26 (receiver) piezoelectric PZT ceramic discs driven by low-frequency, radial/planar excitation (-31 mode), without acoustic matching layers, is also reported here for the first time. The discs are characterised by propagation tank test and directly driven by the inductively coupled power to deliver 29 μW to a receiver (implant) employing a low voltage start-up IC positioned 70 mm deep within a homogeneous liquid phantom. No batteries are used. The deep implant is thus intermittently powered every 800 ms to charge a capacitor which enables its microcontroller, operating with a 500 kHz clock, to transmit a single nibble (4 bits) of digitized sensed data over a period of ~18 ms from deep within the phantom, to the outside world. A power transfer efficiency of 83% using our prototype CMOS logic-gate IC driver is reported for the inductively coupled part of the system. Overall prototype system power consumption is 2.3 W with a total power transfer efficiency of 1% achieved across the tiers

Remote Powering and Data Communication Over a Single Inductive Link for Implantable Medical Devices

RÉSUMÉ Les implants médicaux électroniques (Implantable Medical Devices - IMDs) sont notamment utilisés pour restaurer ou améliorer des fonctions perdues de certains organes. Ils sont capables de traiter des complications qui ne peuvent pas être guéries avec des médicaments ou par la chirurgie. Offrant des propriétés et des améliorations curatives sans précédent, les IMDs sont de plus en plus demandés par les médecins et les patients. En 2017, le marché mondial des IMD était évalué à 15,21 milliards de dollars. D’ici 2025, il devrait atteindre 30,42 mil-liards de dollars, soutenu par un taux de croissance annuel de 9,24% selon le nouveau rapport publié par Fior Markets. Cette expansion entraîne une augmentation des exigences pour as-surer des performances supérieures, des fonctionnalités supplémentaires et une durée de vie plus longue. Ces exigences ne peuvent être satisfaites qu’avec des techniques d’alimentation avancées, un débit de données élevé et une électronique miniaturisée robuste. Construire des systèmes capables de fournir toutes ces caractéristiques est l’objectif principal d’un grand nombre de chercheurs. Parmi plusieurs technologies sans fil, le lien inductif, qui consiste en une paire de bobines à couplage magnétique, est la technique sans fil la plus largement utilisée pour le transfert de puissance et de données. Cela est dû à sa simplicité, sa sécurité et sa capacité à transmettre à la fois de la puissance et des données de façon bidirectionnelle. Cependant, il existe encore un certain nombre de défis concernant la mise en œuvre d’un tel système de transfert d’énergie et de données sans fil (Wireless Power and Data Transfer - WPDT system). Un défi majeur est que les exigences pour une efficacité de transfert d’énergie élevée et pour une communication à haut débit sont contradictoires. En fait, la bande passante doit être élargie pour des débits de données élevés, mais réduite pour une transmission efficace de l’énergie. Un autre grand défi consiste à réaliser un démodulateur fonctionnant à haute vitesse avec une mise en œuvre simple et une consommation d’énergie ultra-faible. Dans ce projet, nous proposons et expérimentons un nouveau système WPDT dédié aux IMD permettant une communication à haute vitesse et une alimentation efficace tout en maintenant une faible consommation d’énergie, une petite surface de silicium et une mise en œuvre simple du récepteur. Le système proposé est basé sur un nouveau schéma de modulation appelé "Carrier Width Modulation (CWM)", ainsi que sur des circuits de modulation et de démodulation inédits. La modulation consiste en un coupe-circuit synchronisé du réservoir LC primaire pendant un ou deux cycles en fonction des données transmises.----------ABSTRACT Implantable Medical Devices (IMDs) are electronic implants notably used to restore or en-hance lost organ functions. They may treat complications that cannot be cured with medica-tion or through surgery. O˙ering unprecedented healing properties and enhancements, IMDs are increasingly requested by physicians and patients. In 2017, the worldwide IMD market was valued at USD 15,21 Billion. By 2025, it is expected to attain USD 30.42 Billion sus-tained by a compound annual growth rate of 9.24% according to a recent report published by Fior Markets. This expansion is bringing-up more demand for higher performance, additional features, and longer device lifespan and autonomy. These requirements can only be achieved with advanced power sources, high-data rates, and robust miniaturized electronics. Building systems able to provide all these characteristics is the main goal of many researchers. Among several wireless technologies, the inductive link, which consists of a magnetically-coupled pair of coils, is the most widely used wireless technique for both power and data transfer. This is due to its simplicity, safety, and ability to provide simultaneously both power and bidirectional data transfer to the implant. However there are still a number of challenges regarding the implementation of such Wireless Power and Data Transfer (WPDT) systems. One main challenge is that the requirements for high Power Transfer Eÿciency (PTE) and for high-data rate communication are contra-dictory. In fact, the bandwidth needs to be widened for high data rates, but narrowed for eÿcient power delivery. Another big challenge is to implement a high-speed demodulator with simple implementation and ultra-low power consumption. In this project, we propose and experiment a new WPDT system dedicated to IMDs allow-ing high-speed communication and eÿcient power delivery, while maintaining a low power consumption, small silicon area, and simple implementation of the receiver. The proposed system is based on a new Carrier Width Modulation (CWM) scheme, as well as novel modu-lation and demodulation circuits. The modulation consists of a synchronized opening of the primary LC tank for one or two cycles according to the transmitted data. Unlike conventional modulation techniques, the data rate of the proposed CWM modulation is not limited by the quality factors of the primary and secondary coils. On the other hand, the proposed CWM demodulator allows higher-speed demodulation and simple implementation, unlike conven-tional demodulators for a similar modulation scheme. It also o˙ers a wide range of data rates under any selected frequency from 10 to 31 MHz

Ultra Low Power FM-UWB Transceiver for High-Density Wireless Sensor Networks

The WiseSkin project aims to provide a non-invasive solution for restoration of a natural sense of touch to persons using prosthetic limbs. By embedding sensor nodes into the silicone coating of the prosthesis, which acts as a sensory skin, WiseSkin targets to provide improved gripping, manipulation and mobility for amputees. Flexibility, freedom of movement and comfort demand unobtrusive, highly miniaturized, low-power sensing capabilities built into the artificial skin, which is then integrated with a sensory feedback system. Wireless communication between the sensor nodes provides more flexibility, better scalability and robustness compared to wired solution, and is therefore a preferred approach for WiseSkin. Design of an RF transceiver tailored for the specific needs of WiseSkin is the topic of this work. The properties of FM ultra-wide band (FM-UWB) modulation make it a good candidate for High-Density Wireless Sensor Networks (HD-WSN). The proposed FM-UWB receivers take advantage of short range to reduce power consumption, and exploit robustness of this wideband modulation scheme. The LNA, identified as the biggest consumer, is removed and signal is directly converted to dc, where amplification and demodulation are performed. Owing to 500 MHz bandwidth, frequency offset and phase noise can be tolerated, and a low-power, free-running ring oscillator can be used to generate the LO signal. The receiver is referred to as an approximate zero-IF receiver. Two receiver architectures are studied. The first one performs quadrature downconversion, and owing to the demodulator linearity, provides the multi-user capability. In the second receiver, quadrature demodulation is replaced by the single-ended one. Due to the nature of the demodulator, sensitivity degrades, and multiple FM-UWB signals cannot be resolved, but the consumption is almost halved compared to the first receiver. The proposed approach is verified through two integrations, both in a standard 65 nm bulk CMOS process. In the first run, a standalone quadrature receiver was integrated. Power consumption of 423 uW was measured, while achieving -70 dBm sensitivity. Good narrow-band interference rejection and multiuser capability with up to 4 FM-UWB channels could be achieved. In the second run, a full transceiver is integrated, with both quadrature and single-ended receivers and a transmitter, all sharing a single IO pad, without the need for any external passive components or switches. The quadrature receiver, with on-chip baseband processing and multi-user support, in this case consumes 550 uW, with a sesensitivity of -68 dBm. The low power receiver consumes 267 uW, and provides -57 dBm sensitivity, at a single FM-UWB channel. The implemented trantransmitter transmits a 100 kb/s FM-UWB signal at -11.4 dBm, while drawing 583 uW from the 1 V supply. The on-chip clock recovery allows reference frequency offset up to 8000 ppm. Since state of the art on-chip RC oscillators can provide below 2100 ppm across the temperature range of interest, the implemented transceiver demonstrates the feasibility of a fully integrated FM-UWB radio with no need for a quartz reference or any external components. In addition, the transceiver can tolerate up to 3 dBm narrow-band interferer at 2.4 GHz. Such a strong signal can be used to remotely power the sensor nodes inside the artificial skin and enable a truly wirelessWiseSkin solution