Energy-Efficient Capacitance-to-Digital Converters for Low-Energy Sensor Nodes

摘要

Energy efficiency is a key requirement for wireless sensor nodes, biomedical implants,udand wearable devices. The energy consumption of the sensor node needs toudbe minimized to avoid battery replacement, or even better, to enable the device toudsurvive on energy harvested from the ambient. Capacitive sensors do not consumeudstatic power; thus, they are attractive from an energy efficiency perspective. In addition,udthey can be employed in a wide range of sensing applications. However, theudsensor readout circuit–i.e., the capacitance-to-digital converter (CDC)–can be theuddominant source of energy consumption in the system. Thus, the development ofudenergy-efficient CDCs is crucial to minimizing the energy consumption of capacitiveudsensor nodes.udIn the first part of this dissertation, we propose several energy-efficient CDC architecturesudfor low-energy sensor nodes. First, we propose a digitally-controlled coarsefineudmultislope CDC that employs both current and frequency scaling to achieveudsignificant improvement in energy efficiency. Second, we analyze the limitations ofudsuccessive approximation (SAR) CDC, and we address these limitations by proposinguda robust parasitic-insensitive opamp-based SAR CDC. Third, we propose anudinverter-based SAR CDC that achieves an energy efficiency figure-of-merit (FoM)udof 31fJ/Step, which is the best energy efficiency FoM reported to date. Fourth, we propose a differential SAR CDC with quasi-dynamic operation to maintain excellentudenergy efficiency for a scalable sample rate.udIn the second part of this dissertation, we study the matching properties of smalludintegrated capacitors, which are an integral component of energy-efficient CDCs. Despiteudconventional wisdom, we experimentally illustrate that the mismatch of smalludcapacitors can be directly measured, and we report mismatch measurements for subfemtofaradudintegrated capacitors. We also correct the common misconception thatudlateral capacitors match better than vertical capacitors, and we identify the conditionsudthat make one implementation preferable.udIn the third and last part of this dissertation, we investigate the potential of noveludmetal-organic framework (MOF) thin films in capacitive gas sensing. We provideudsensitivity-based optimization and simple fabrication flow for capacitive interdigitatedudelectrodes. We use a custom flexible gas sensor test setup that is designed and builtudin-house to characterize MOF-based capacitive gas sensors.