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

Whole-Body MRI and Ethnic Differences in Adipose Tissue and Skeletal Muscle Distribution in Overweight Black and White Adolescent Boys

It is unclear whether ethnic differences exist in adipose tissue (AT) and skeletal muscle (SM) distribution in black and white youth. Investigation into the pattern of AT and SM distribution in black versus white youth may provide insight into the previously reported health disparities between these ethnicities. Therefore, we examined total and regional AT and SM in overweight black and white boys. The study sample included overweight black (n = 19) and white (n = 21) boys (11–18 yr, BMI ≥ 85th) whose body composition was evaluated using whole-body MRI. Despite similar age, Tanner stage, and BMI, black boys had significantly (P < .05) less visceral AT than white boys and more (P < .05) total and lower-body subcutaneous AT (SAT) in both absolute (kg) and relative (%) terms. There was a main effect (P < .05) of ethnicity on the relationship between total and regional AT, such that for a given amount of total body AT (kg), black boys had a greater (P < .05) lower-body SAT and less visceral AT than their white peers. For a given amount of total SM, black boys had more (P < .05) SM in the thigh. Compared with overweight white boys, overweight black boys have less visceral fat, more subcutaneous fat, and more thigh skeletal muscle

Effects of Exercise Alone on Insulin Sensitivity and Glucose Tolerance in Obese Youth

As with the dramatic increases in childhood obesity over the past decades, the incidence of type 2 diabetes has increased among children and adolescents in the United States. Insulin resistance is a common feature of childhood obesity and increases the risk of type 2 diabetes, metabolic syndrome, and atherogenic lipoprotein profile in obese youth. Although cross-sectional studies report beneficial effects of physical activity or cardiorespiratory fitness on insulin sensitivity, the role of regular exercise alone (e.g., no calorie restriction) as a strategy to reduce the risk of type 2 diabetes is unclear in obese children and adolescents. In this mini review, we examined the independent effects of various exercise on glucose tolerance and insulin sensitivity in obese youth

Dual Piezoelectric Energy Investing and Harvesting Interface for High-Voltage Input

A novel harvesting interface for multiple piezoelectric transducers (PZTs) is proposed for high-voltage energy harvesting. Pre-biasing a PZT prior to its mechanical deformation increases its damping force, resulting in higher energy extraction. Unlike the conventional harvesters where a PZT-generated output is assumed to be continuous sinusoidal and output polarity is assumed to be alternating every cycle, PZT-generated output from human motion is expected to be random. Therefore, in the proposed approach, energy is invested to the PZT only when PZT deformation is detected. Upon the motion detection, energy stored at a storage capacitor (CSTOR) from earlier energy harvesting cycle is invested to pre-bias PZT, enhancing energy extraction. The harvested energy is transferred to back CSTOR for energy investment on the next cycle and then excess energy is transferred to the battery. In addition, partial electric charge extraction (PECE) is adapted to extract a partial amount of charges from the PZT every time its voltage approaches the process limit of 40 V. Simulations with 0.35 µm BCD process show 7.61× (with PECE only) and 8.38× (with PECE and energy investment) improvement compared to the conventional rectifier-based harvesting scheme Proposed harvesting interface successfully harvests energy from excitations with open-circuit voltages up to 100 V

A High-Voltage Energy-Harvesting Interface for Irregular Kinetic Energy Harvesting in IoT Systems with 1365% Improvement Using All-NMOS Power Switches and Ultra-low Quiescent Current Controller

An energy-harvesting interface for kinetic energy harvesting from high-voltage piezoelectric and triboelectric generators is proposed in this paper. Unlike the conventional kinetic energy-harvesting interfaces optimized for continuous sinusoidal input, the proposed harvesting interface can efficiently handle irregular and random high voltage energy inputs. An N-type mosfet (NMOS)-only power stage design is introduced to simplify power switch drivers and minimize conduction loss. Controller active mode power is also reduced by introducing a new voltage peak detector. For efficient operation with potentially long intervals between random kinetic energy inputs, standby power consumption is minimized by monitoring the input with a 43 pW wake-up controller and power-gating all other circuits during the standby intervals. The proposed harvesting interface can harvest energy from a wide range of energy inputs, 10 s of nJ to 10 s of &micro;J energy/pulse, with an input voltage range of 5&ndash;200 V and an output range of 2.4&ndash;4 V under discontinuous as well as continuous excitation. The proposed interface is examined in two scenarios, with integrated power stage devices (maximum input 45 V) and with discrete power stage devices (maximum input 200 V), and the harvesting efficiency is improved by up to 600% and 1350%, respectively, compared to the case when harvesting is performed with a full bridge rectifier

A Wide Load Current and Voltage Range Switched Capacitor DC–DC Converter with Load Dependent Configurability for Dynamic Voltage Implementation in Miniature Sensors

Advancements in low power circuits and batteries have enabled the design of miniature sensors with tiny batteries. In such systems, implementing dynamic voltage scaling (DVS) is crucial for maximizing system lifetime. In this paper, a new switched capacitor (SC) converter that is capable of handling a wide range of load currents and output voltages is presented for on-chip DVS implementation. The proposed converter consists of multi-ratio multi-leaf SC stages and reconfigurable interconnect, enabling fine voltage resolution. The stage interconnect scheme enables cascaded or parallel connection of stages. The multi-leaf structure allows load-dependent switch size selection, offering a better trade-off between losses over a wide load range. A limited-voltage-swing switch-driving scheme allows efficient down-conversion from high battery voltage input. A prototype was fabricated in a 180 nm process, providing an output voltage with effective resolution of 16 mV over a load current range of 300 nA to 300 &#956;A (1000&#215;) from a 4 V battery. Efficiency greater than 62% and a peak efficiency of 77% are achieved under a light load (500 nA) over a voltage range of 400 mV to 1.6 V. Efficiency greater than 64% and a peak efficiency of 72% are achieved under a heavy load (200 &#956;A) over a voltage range of 700 mV to 1.6 V