A 1.1 nW Energy-Harvesting System with 544 pW Quiescent Power for Next-Generation Implants

This paper presents a nW power management unit (PMU) for an autonomous wireless sensor that sustains itself by harvesting energy from the endocochlear potential (EP), the 70-100 mV electrochemical bio-potential inside the mammalian ear. Due to the anatomical constraints inside the inner ear, the total extractable power from the EP is limited close to 1.1-6.25 nW. A nW boost converter is used to increase the input voltage (30-55 mV) to a higher voltage (0.8-1.1 V) usable by CMOS circuits in the sensor. A pW charge pump circuit is used to minimize the leakage in the boost converter. Furthermore, ultralow-power control circuits consisting of digital implementations of input impedance adjustment circuits and zero current switching circuits along with Timer and Reference circuits keep the quiescent power of the PMU down to 544 pW. The designed boost converter achieves a peak power conversion efficiency of 56%. The PMU can sustain itself, and a duty-cyled ultralow-power load while extracting power from the EP of a live guinea pig. The PMU circuits have been implemented on a 0.18- μm CMOS process.Semiconductor Research Corporation. Focus Center for Circuit and System Solutions (C2S2)Interconnect Focus Center (United States. Defense Advanced Research Projects Agency and Semiconductor Research Corporation)National Institutes of Health (U.S.) (Grant K08 DC010419)National Institutes of Health (U.S.) (Grant T32 DC00038)Bertarelli Foundatio

A pW-Power Hz-Range Oscillator Operating With a 0.3-1.8-V Unregulated Supply

In this paper, a pW-power relaxation oscillator for sensor node applications is presented. The proposed oscillator operates over a wide supply voltage range from nominal down to deep sub-threshold and requires only a sub-pF capacitor for Hz-range output frequency. A true pW-power operation is enabled thanks to the adoption of an architecture leveraging transistor operation in super-cutoff, the elimination of voltage regulation, and current reference. Indeed, the oscillator can be powered directly from highly variable voltage sources (e.g., harvesters and batteries over their whole charge/discharge cycle). This is achieved thanks to the wide supply voltage range, the low voltage sensitivity of the output frequency and the current drawn from the supply. A test chip of the proposed oscillator in 180 nm exhibits a nominal frequency of approximately 4 Hz, a supply voltage range from 1.8 V down to 0.3 V with 10%/V supply sensitivity, 8-18-pA current absorption, and 4%/°C thermal drift from -20 °C to 40 °C at an area of 1600 μm². To the best of the authors' knowledge, the proposed oscillator is the only one able to operate from sub-threshold to nominal voltage

Thermoelectric Power Harvesting for Biomedical Implants

The modern healthcare industry relies on the use of implantable monitoring devices to obtain potentially life-saving data. This has led to the necessity for small, long-lasting batteries to be used in these devices. In order to replace a device’s battery, patients often undergo invasive surgery. This surgery can be costly and physically strenuous for the patient; thus, there is a desire to minimize the frequency of battery replacement. The goal of this research is to develop an integrated circuit that can supply harvested energy to an implantable monitoring device so as to extend implant batteries’ lifetime. These monitoring devices are often implanted just below the skin of a patient, where natural temperature gradients exist. Using the well-known physical principle called the Seebeck effect, these temperature gradients can be exploited to produce electrical power by using a specialized device called a thermoelectric generator. With some additional circuitry, this harvested energy can be used in place of the battery to supply power to the implanted device. Such circuitry includes a switching regulator with a PWM controller, an oscillator, and digital logic. The thermoelectric generator can harvest enough energy to power the device, but the voltage produced is generally too low to be used. Thus, the voltage must be stepped up to a higher value. The switching regulator topology best suited for this purpose is the DC-DC boost converter due to its high efficiency. However, the amount of power harvested is small, so this paper has a major emphasis on power consumption optimization for each circuit block added. Also, the boost converter must use feedback in order to regulate the output to a constant voltage, so a controller was designed and implemented for this purpose. An additional feedforward path was added to perform an impedance match between the source resistance and the boost converter to reduce the charge time of the output capacitor. An oscillator was needed to switch transistors in the boost converter and provide the synchronicity needed in the digital logic blocks. Finally, the last circuitry developed was digital logic to control the startup procedure and choose to use either the harvested energy or the battery to power the implanted device. This paper will discuss the design procedure for each of the mentioned circuit blocks and provide the results of the research conducted

On-Chip Solar Energy Harvester and PMU With Cold Start-Up and Regulated Output Voltage for Biomedical Applications

This paper presents experimental results from a system that comprises a fully autonomous energy harvester with a solar cell of 1 mm 2 as energy transducer and a Power Management Unit (PMU) on the same silicon substrate, and an output voltage regulator. Both chips are implemented in standard 0.18 μm CMOS technology with total layout areas of 1.575 mm 2 and 0.0126 mm 2 , respectively. The system also contains an off-the-shelf 3.2 mm × 2.5 mm × 0.9 mm supercapacitor working as an off-chip battery or energy reservoir between the PMU and the voltage regulator. Experimental results show that the fast energy recovery of the on-chip solar cell and PMU permits the system to replenish the supercapacitor with enough charge as to sustain Bluetooth Low Energy (BLE) communications even with input light powers of 510 nW. The whole system is able to self-start-up without external mechanisms at 340 nW. This work is the first step towards a self-supplied sensor node with processing and communication capabilities. The small form factor and ultra-low power consumption of the system components is in compliance with biomedical applications requirementsThis work was supported in part by the Spanish Government (Ministerio de Ciencia, Innovación y Universidades) under Project RTI2018-097088-B-C32 and Project RTI2018-095994-B-I00 (MICINN/FEDER), in part by the Xunta de Galicia, in part by the Consellería de Cultura, Educación e Ordenación Universitaria (accreditation 2016-2019, ED431G/08 and reference competitive group 2017-2020, ED431C 2017/69) and European Regional Development Fund (ERDF), and in part by the Junta de Extremadura and the ERDF, under Grant IB 18079S

A Biofuel-Cell-Based Energy Harvester With 86% Peak Efficiency and 0.25-V Minimum Input Voltage Using Source-Adaptive MPPT

This article presents an efficient cold-starting energy harvester system, fabricated in 65-nm CMOS. The proposed harvester uses no external electrical components and is compatible with biofuel-cell (BFC) voltage and power ranges. A power-efficient system architecture is proposed to keep the internal circuitry operating at 0.4 V while regulating the output voltage at 1 V using switched-capacitor dc–dc converters and a hysteretic controller. A startup enhancement block is presented to facilitate cold startup with any arbitrary input voltage. A real-time on-chip 2-D maximum power point tracking with source degradation tracing is also implemented to maintain power efficiency maximized over time. The system performs cold startup with a minimum input voltage of 0.39 V and continues its operation if the input voltage degrades to as low as 0.25 V. Peak power efficiency of 86% is achieved at 0.39 V of input voltage and 1.34 μW of output power with 220 nW of average power consumption of the chip. The end-to-end power efficiency is kept above 70% for a wide range of loading powers from 1 to 12 μW. The chip is integrated with a pair of lactate BFC electrodes with 2 mm of diameter on a prototype-printed circuit board (PCB). Integrated operation of the chip with the electrodes and a lactate solution is demonstrated

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

Power Management ICs for Internet of Things, Energy Harvesting and Biomedical Devices

This dissertation focuses on the power management unit (PMU) and integrated circuits (ICs) for the internet of things (IoT), energy harvesting and biomedical devices. Three monolithic power harvesting methods are studied for different challenges of smart nodes of IoT networks. Firstly, we propose that an impedance tuning approach is implemented with a capacitor value modulation to eliminate the quiescent power consumption. Secondly, we develop a hill-climbing MPPT mechanism that reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits. Furthermore, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations as low as 12 µW. Thirdly, we introduce a reconfigurable charge pump to provide the hybrid conversion ratios (CRs) as 1⅓× up to 8× for minimizing the charge redistribution loss. The reconfigurable feature also dynamically tunes to maximum power point tracking (MPPT) with the frequency modulation, resulting in a two-dimensional MPPT. Therefore, the voltage conversion efficiency (VCE) and the power conversion efficiency (PCE) are enhanced and flattened across a wide harvesting range as 0.45 to 3 V. In a conclusion, we successfully develop an energy harvesting method for the IoT smart nodes with lower cost, smaller size, higher conversion efficiency, and better applicability. For the biomedical devices, this dissertation presents a novel cost-effective automatic resonance tracking method with maximum power transfer (MPT) for piezoelectric transducers (PT). The proposed tracking method is based on a band-pass filter (BPF) oscillator, exploiting the PT’s intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting (UVSD) system. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin. Furthermore, a combined sensing scheme circuit allows multiple surgical tissue debulking, vessel sealer and dissector (VSD) technologies to operate from the same sensing scheme board. Its advantage is that a single driver controller could be used for both systems simplifying the complexity and design cost. In a conclusion, we successfully develop an ultrasonic scalpel to replace the other electrosurgical counterparts and the conventional scalpels with lower cost and better functionality

Design of Low-Cost Energy Harvesting and Delivery Systems for Self-Powered Devices: Application to Authentication IC

This thesis investigates the development of low-cost energy harvesting and delivery systems for low-power low-duty-cycle devices. Initially, we begin by designing a power management scheme for on-demand power delivery. The baseline implementation is also used to identify critical challenges for low-power energy harvesting. We further propose a robust self-powered energy harvesting and delivery system (EHDS) design as a solution to achieve energy autonomy in standalone systems. The design demonstrates a complete ecosystem for low-overhead pulse-frequency modulated (PFM) harvesting while reducing harvesting window confinement and overall implementation footprint. Two transient-based models are developed for improved accuracy during design space exploration and optimization for both PFM power conversion and energy harvesting. Finally, a low-power authentication IC is demonstrated and projected designs for self-powered System-on-Chips (SoCs) are presented. The proposed designs are proto-typed in two test-chips in a 65nm CMOS process and measurement data showcase improved performance in terms of battery power, cold-start duration, passives (inductance and capacitance) needed, and end-to-end harvesting/conversion efficiency.Ph.D

Power Management Circuits for Energy Harvesting Applications

Energy harvesting is the process of converting ambient available energy into usable electrical energy. Multiple types of sources are can be used to harness environmental energy: solar cells, kinetic transducers, thermal energy, and electromagnetic waves. This dissertation proposal focuses on the design of high efficiency, ultra-low power, power management units for DC energy harvesting sources. New architectures and design techniques are introduced to achieve high efficiency and performance while achieving maximum power extraction from the sources. The first part of the dissertation focuses on the application of inductive switching regulators and their use in energy harvesting applications. The second implements capacitive switching regulators to minimize the use of external components and present a minimal footprint solution for energy harvesting power management. Analysis and theoretical background for all switching regulators and linear regulators are described in detail. Both solutions demonstrate how low power, high efficiency design allows for a self-sustaining, operational device which can tackle the two main concerns for energy harvesting: maximum power extraction and voltage regulation. Furthermore, a practical demonstration with an Internet of Things type node is tested and positive results shown by a fully powered device from harvested energy. All systems were designed, implemented and tested to demonstrate proof-of-concept prototypes