Ultra-Low Power Circuit Design for Cubic-Millimeter Wireless Sensor Platform.

Modern daily life is surrounded by smaller and smaller computing devices. As Bell’s Law predicts, the research community is now looking at tiny computing platforms and mm3-scale sensor systems are drawing an increasing amount of attention since they can create a whole new computing environment. Designing mm3-scale sensor nodes raises various circuit and system level challenges and we have addressed and proposed novel solutions for many of these challenges to create the first complete 1.0mm3 sensor system including a commercial microprocessor. We demonstrate a 1.0mm3 form factor sensor whose modular die-stacked structure allows maximum volume utilization. Low power I2C communication enables inter-layer serial communication without losing compatibility to standard I2C communication protocol. A dual microprocessor enables concurrent computation for the sensor node control and measurement data processing. A multi-modal power management unit allowed energy harvesting from various harvesting sources. An optical communication scheme is provided for initial programming, synchronization and re-programming after recovery from battery discharge. Standby power reduction techniques are investigated and a super cut-off power gating scheme with an ultra-low power charge pump reduces the standby power of logic circuits by 2-19× and memory by 30%. Different approaches for designing low-power memory for mm3-scale sensor nodes are also presented in this work. A dual threshold voltage gain cell eDRAM design achieves the lowest eDRAM retention power and a 7T SRAM design based on hetero-junction tunneling transistors reduces the standby power of SRAM by 9-19× with only 15% area overhead. We have paid special attention to the timer for the mm3-scale sensor systems and propose a multi-stage gate-leakage-based timer to limit the standard deviation of the error in hourly measurement to 196ms and a temperature compensation scheme reduces temperature dependency to 31ppm/°C. These techniques for designing ultra-low power circuits for a mm3-scale sensor enable implementation of a 1.0mm3 sensor node, which can be used as a skeleton for future micro-sensor systems in variety of applications. These microsystems imply the continuation of the Bell’s Law, which also predicts the massive deployment of mm3-scale computing systems and emergence of even smaller and more powerful computing systems in the near future.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91438/1/sori_1.pd

Ultra-Low Power Optical Interface Circuits for Nearly Invisible Wireless Sensor Nodes.

Technological advances in the semiconductor industry and integrated circuit design have resulted in electronic devices that are smaller and cheaper than ever, and yet they are more pervasive and powerful than what could hardly be imagined several decades ago. Nowadays, small hand-held devices such as smartphones have completely reshaped the way people communicate, share information, and get entertained. According to Bell’s Law, the next generation of computers will be cubic-millimeter-scale in volume with more prevalent presence than any other computing platform available today, opening up myriad of new applications. In this dissertation, a millimeter-scale wireless sensor node for visual sensing applications is proposed, with emphasis on the optical interface circuits that enable wireless optical communication and visual imaging. Visual monitoring and imaging with CMOS image sensors opens up a variety of new applications for wireless sensor nodes, ranging from surveillance to in vivo molecular imaging. In particular, the ability to detect motion can enable intelligent power management through on-demand duty cycling and reduce the data storage requirement. Optical communication provides an ultra-low power method to wirelessly control or transmit data to the sensor node after encapsulation and deployment. The proposed wireless sensor node is a nearly-invisible, yet a complete system with imaging, optics, two-way wireless communication, CPU, memory, battery and energy harvesting with solar cells. During its ultra-low power motion detection mode, the overall power consumption is merely 304 nW, allowing energy autonomous continuous operation with 10 klux of background lighting. Such complete features in the unprecedented form factor can revolutionize the role of electronics in our future daily lives, taking the “Smart Dust” concept from fiction to reality.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/110399/1/coolkgh_1.pd

Slocalization: Sub-{\mu}W Ultra Wideband Backscatter Localization

Ultra wideband technology has shown great promise for providing high-quality location estimation, even in complex indoor multipath environments, but existing ultra wideband systems require tens to hundreds of milliwatts during operation. Backscatter communication has demonstrated the viability of astonishingly low-power tags, but has thus far been restricted to narrowband systems with low localization resolution. The challenge to combining these complimentary technologies is that they share a compounding limitation, constrained transmit power. Regulations limit ultra wideband transmissions to just -41.3 dBm/MHz, and a backscatter device can only reflect the power it receives. The solution is long-term integration of this limited power, lifting the initially imperceptible signal out of the noise. This integration only works while the target is stationary. However, stationary describes the vast majority of objects, especially lost ones. With this insight, we design Slocalization, a sub-microwatt, decimeter-accurate localization system that opens a new tradeoff space in localization systems and realizes an energy, size, and cost point that invites the localization of every thing. To evaluate this concept, we implement an energy-harvesting Slocalization tag and find that Slocalization can recover ultra wideband backscatter in under fifteen minutes across thirty meters of space and localize tags with a mean 3D Euclidean error of only 30 cm.Comment: Published at the 17th ACM/IEEE Conference on Information Processing in Sensor Networks (IPSN'18

Accurate Power Consumption Evaluation forPeripherals in Ultra Low-Power embedded systems

International audienceWe propose a methodology to measure, model and simulate power consumption of peripheral devices of a lowpower embedded micro-controller, while keeping a reasonable development cost. This methodology is experimented against the low-power MSP-EXP430FR5739 platform that includes nonvolatile RAM for intermittent computing purposes and a handful of peripherals. The experimental measurements enable the characterization of the consumption of the peripherals, while many existing comparable studies do not provide power consumption for peripherals. These measurements are integrated into a simulator that targets low-power peripheral-intensive applications, as are most of IoT embedded programs. The accuracy of the power consumption estimation is within a 5% error on intermittent embedded computing using peripherals

Sytare: Persistence de l'état des périphériques pour les systèmes à alimentation intermittente

National audienceLes systèmes dits à alimentation intermittente sont de petits systèmes embarqués récupérant l'énergie dans leur environnement. À cause de contraintes de taille et de coût, ils subissent de fréquentes coupures de courant, mais sont néanmoins capables d'exécuter un programme logiciel, en sauvegardant les données nécessaires au calcul dans une mémoire non-volatile. Cet article présente une technique permettant à ces systèmes d'utiliser des périphériques non triviaux tels qu'un convertisseur analogique-numérique, une interface série ou une radio

MPU-based incremental checkpointing for transiently-powered systems

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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