There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A Review on Internet of Things Solutions for Intelligent Energy Control in Buildings for Smart City Applications

A building energy management system (BEMS) is a sophisticated method used for monitoring and controlling a building’s energy requirements A number of potential studies were conducted in nearly or net zero energy buildings (nZEBs) for the optimization of building energy consumption through efficient and sustainable ways Moreover, policy makers are approving measures to improve building energy efficiency in order to foster sustainable energy usages However, the intelligence of existing BEMSs or nZEBs is inadequate, because of the static set points for heating, cooling, and lighting, the complexity of large amounts of BEMS data, data loss, and network problems To solve these issues, a BEMS or nZEB solution based on the Internet of energy (IoE) provides disruptive opportunities for revolutionizing sustainable building energy management This paper presents a critical review of the potential of an IoE-based BEMS for enhancing the performance of future generation building energy utilization The detailed studies of the IoE architecture, typical nZEB configuration, different generations of nZEB, and smart building energy systems for future BEMS are investigated The operations, advantages, and limitations of the existing BEMSs or nZEBs are illustrated A comprehensive review of the different types of IoE-based BEMS technologies, such as energy routers, storage systems and materials, renewable sources, and plug-and-play interfaces, is then presented The rigorous review indicates that existing BEMSs require advanced controllers integrated with IoE-based technologies for sustainable building energy usage The main objective of this review is to highlight several issues and challenges of the conventional controllers and IoE applications of BEMSs or nZEBs Accordingly, the review provides several suggestions for the research and development of the advanced optimized controller and IoE of future BEMSs All the highlighted insights and recommendations of this review will hopefully lead to increasing efforts toward the development of the future BEMS applications

A Review of Internet of Energy Based Building Energy Management Systems: Issues and Recommendations

This paper presents a fully integrated energy harvester that maintains >35% end-to-end efficiency when harvesting from a 0.84 mm 2
 solar cell in low light condition of 260 lux, converting 7 nW input power from 250 mV to 4 V. Newly proposed self-oscillating switched-capacitor (SC) DC-DC voltage doublers are cascaded to form a complete harvester, with configurable overall conversion ratio from 9× to 23×. In each voltage doubler, the oscillator is completely internalized within the SC network, eliminating clock generation and level shifting power overheads. A single doubler has >70% measured efficiency across 1 nA to 0.35 mA output current ( >10 5
 range) with low idle power consumption of 170 pW. In the harvester, each doubler has independent frequency modulation to maintain its optimum conversion efficiency, enabling optimization of harvester overall conversion efficiency. A leakage-based delay element provides energy-efficient frequency control over a wide range, enabling low idle power consumption and a wide load range with optimum conversion efficiency. The harvester delivers 5 nW-5 μW output power with >40% efficiency and has an idle power consumption 3 nW, in test chip fabricated in 0.18 μm CMOS technology.

An Ultra-Low Power Fully Integrated Energy Harvester Based on Self-Oscillating Switched-Capacitor Voltage Doubler

A boost converter for thermoelectric energy harvesting in 130 nm CMOS achieves energy harvesting from a 10 mV input, which allows wearable body sensors to continue operation with low thermal gradients. The design uses a peak inductor current control scheme and duty cycled, offset compensated comparators to maintain high efficiency across a broad range of input and output voltages. The measured efficiency ranges from 53% at ${\rm V}_{\rm I}=20\ {\hbox{mV}}$ to a peak efficiency of 83% at ${\rm V}_{\rm I}=300\ {\hbox{mV}}$ . A cold-start circuit starts the operation of the boost converter from 220 mV, and an RF kick-start circuits starts it from $-$ 14.5 dBm at 915 MHz RF power.

A 10 mV-Input Boost Converter With Inductor Peak Current Control and Zero Detection for Thermoelectric and Solar Energy Harvesting With 220 mV Cold-Start and $-$ 14.5 dBm, 915 MHz RF Kick-Start

The Internet of Things (IoT) is a rapidly emerging application space, poised to become the largest electronics market for the semiconductor industry. IoT devices are focused on sensing and actuating of our physical environment and have a nearly unlimited breadth of uses. In this paper, we explore the IoT application space and then identify two common challenges that exist across this space: ultra-low power operation and system design using modular, composable components. We survey recent low power techniques and discuss a low power bus that enables modular design. Finally, we conclude with three example ultra-low power, millimeter-scale IoT systems.

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IoT design space challenges: Circuits and systems

Capacitance sensors are widely used to measure various physical quantities, including position, pressure, and concentration of certain chemicals [1-6]. Integrating capacitive sensors into a small wireless sensor system is challenging due to their large power consumption relative to the total system power/energy budget, which can be as low as a few nW [4]. Typical capacitance-to-digital converters (CDCs) use charge sharing or charge transfer between capacitors to convert the sampled capacitance to voltage, which is then measured with an ADC [1-6]. This approach requires complex analog circuits, such as amplifiers and ADCs, increasing design complexity and often increasing power consumption. Moreover, the initial capacitance to voltage conversion essentially limits the input capacitance range because of output voltage saturation. This paper presents a fully digital CDC that is based on the observation that when a ring oscillator (RO) is powered from a charged capacitance, the number of RO cycles required to discharge the capacitance to a fixed voltage is naturally linear with the capacitance value. This observation enables a simple, fully digital conversion scheme that is inherently linear. As a result, the proposed CDC performs conversion across a very wide capacitance range from 0.7pF to over 10nF with < 0.06% linearity error. The CDC senses 11.3pF input capacitance with 35.1 pJ conversion energy and 141fJ/c-s FoM.

27.6 A 0.7pF-to-10nF fully digital capacitance-to-digital converter using iterative delay-chain discharge

A dual-slope capacitance-to-digital converter for pressure-sensing is presented and demonstrated in a complete microsystem. The design uses base capacitance subtraction with a configurable capacitor bank to narrow down input capacitance range and reduce conversion time. An energy-efficient iterative charge subtraction method is proposed, employing a current mirror that leverages the 3.6 V battery supply available in the system. We also propose dual-precision comparators to reduce comparator power while maintaining high accuracy during slope conversion, further improving energy efficiency. The converter occupies 0.105 mm $^{2}$ in 180 nm CMOS and achieves 44.2 dB SNR at 6.4 ms conversion time and 110 nW of power, corresponding to 5.3 pJ/conv-step FoM. The converter is integrated with a pressure transducer, battery, processor, power management unit, and radio to form a complete 1.4 mm $\times$ 2.8 mm $\times$ 1.6 mm pressure sensor system aimed at implantable devices. The multi-layer system is implemented in 180 nm CMOS. The system was tested for resolution in a pressure chamber with an external 3.6 V supply and serial communication bus, and the measured resolution of 0.77 mmHg was recorded. We also demonstrated the wireless readout of the pressure data on the stack system operating completely wirelessly using an integrated battery.

A Dual-Slope Capacitance-to-Digital Converter Integrated in an Implantable Pressure-Sensing System

Recent advances in low-power circuits have enabled mm-scale wireless systems [1] for wireless sensor networks and implantable devices, among other applications Energy harvesting is an attractive way to power such systems due to limited energy capacity of batteries at these form factors However, the same size limitation restricts the amount of harvested power, which can be as low as 10s of nW for mm-scale photovoltaic cells in indoor conditions Efficient DC-DC up-conversion at such low power levels (for battery charging) is extremely challenging and has not yet been demonstrated

Sechang Oh

Papers

IoT design space challenges: Circuits and systems

An Ultra-Low Power Fully Integrated Energy Harvester Based on Self-Oscillating Switched-Capacitor Voltage Doubler

27.6 A 0.7pF-to-10nF fully digital capacitance-to-digital converter using iterative delay-chain discharge

A Dual-Slope Capacitance-to-Digital Converter Integrated in an Implantable Pressure-Sensing System

23.3 A 3nW fully integrated energy harvester based on self-oscillating switched-capacitor DC-DC converter