| New alarm system applications in industries such as home security or environmental monitoring can be implemented using wake-up sensors created from smart dust, millimeter-scale wireless sensor nodes, that are enabled by combining micro-electro-mechanical (MEM) sensors and nanowatt mixed-signal CMOS sensor front-end circuits. Nanowatt power consumption and minimum leakage current enable always-on operation and long lifetime from small batteries. The present work focuses on the analysis, design, simulation, and experimental characterization of nanowatt CMOS sensor front-ends, MEMS relay-based power electronics for minimum leakage DC/DC conversion, and MEMS transducer-based ultrasonic range finding to locate the source that triggers the alarm. Three architectures for nanowatt front-ends are presented, followed by comparisons between the architectures, design tradeoffs, and experimental results. Theoretical equations, simulations, and measurements are presented on three DC/DC converters: a self-starting charge transfer regulator, a buck converter, and a boost converter. Last, the design and experimental characterization of a monolithic MEMS-CMOS piezoelectric micro-machined ultrasonic transducer (PMUT) for range finding applications that incorporates a variable gain stage and clip-detection circuit is presented. These technologies can be integrated into future wake-up sensors to support numerous applications in the Internet of Things. |
