Low-Power Energy Efficient Circuit Techniques for Small IoT Systems
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As the benefit of technology scaling has been more limited in recent years, alternative ways to improve the power of circuit designs have been proposed, and broadening the application areas of the circuit is one of them. Internet of Things (IoT) has become one of these application areas that are actively explored nowadays, as the scaling trends of size, power and cost reduction are continuing. These continuing trends lead to the development of many new sensor systems with affordable costs for IoT applications, and this functional diversification and broadened interaction with the outside environment will offer people convenient connection and control over all the matters around them.
This dissertation discusses major challenges and their solutions in realizing small IoT systems, focusing on non-digital blocks such as power converters and analog sensing blocks that have difficulty in following the traditional scaling trends of digital circuits. To overcome a limitation of both the energy storage capacity and energy harvesting availability in small IoT systems, the dissertation presents an efficient energy harvester and a power management unit with low quiescent power consumption and good efficiency in ultra-low power ranges.
To further improve the power efficiency of these systems, analog circuits essential to most wireless IoT systems are also discussed and improved. A capacitance-to-digital sensor interface and a clocked comparator design are improved in both area and energy efficiency, by their digital-like implementation and operation in phase and frequency domain.
Finally, a technique for removing dynamic voltage and temperature variation is presented, as smaller circuits in advanced technologies are more and more affected of this variation. A 2-D simultaneous feedback control using on-chip oven control is used to cancel external voltage and temperature changes.