Design of an Integrated Low-Power Capacitive Sensor Readout Circuit

This book reports the development of an integrated§low-power readout circuit for a capacitive sensor§with 40 - 60 pF basic capacitance. The sensor is used§to detect screw loosening in an osteosynthesis§measurement system. To ensure detection of screw§loosening the readout circuit must be able to measure§capacitance changes of at least 0.25 pF. Several§readout techniques for capacitive sensors are§investigated and evaluated for this application.§Finally two types are developed and simulated, a§Wien-bridge oscillator and a switched capacitor (SC)§capacitance to voltage (C/V) converter. The§oscillator is simulated with Cadence in a 0.35 µm§triple-well, 4-metal, and double poly CMOS process§from austriamicrosystems. The Wien-bridge is adapted§for CMOS integration. Additionally, a SC§C/V-converter is developed and simulated in the same§process to compare the readout techniques. The target§audience for this book are electronic engineers,§students and people who are interested in working and§developing with simulation tools.