| This dissertation explores generic multi-parameter sensing systems for portable wireless applications where power, size, and performance are critically important. Using state-of-the-art microelectronic and microelectromechanical system (MEMS) technologies, such microsystems are evolving toward packaged volumes of 1cc, power dissipation levels of less than 1mW, communication ranges of 1km, and levels of accuracy and reliability significantly above those of stand-alone devices. A prototype microinstrumentation system was developed to address these goals and identify remaining challenges. The system utilizes an open architecture compatible with a variety of low-bandwidth (<10kHz) transducers and employs a nine-line serial intramodule sensor bus having interrupt capability and permitting both analog and digital data formats. A custom integrated circuit interfaces up to six capacitive sensors to the bus with 1fF resolution. Transducer gain and offset can be adjusted on-line using on-chip RAM. The interface chip accepts base capacitances from 0.15pF to 8pF and provides sensitivities from 0.23 to 73mV/fF. This prototype system employed temperature, pressure, humidity, and acceleration sensors and achieved a size of 10cc, a time-averaged power dissipation of 550muW, and a data transmission range of 50m.;Readout circuit interfaces compatible with very high sensor performance at small size and low power were found to be a primary challenge to the continued evolution of such microsystems. These problems were explored through the development of a second-generation interface circuit. This highly-programmable BiCMOS chip can read out five capacitive elements having base capacitances from 16fF to 40pF, can provide sensitivities from 20.8muV/fF to 1mV/fF, and has a resolution of 1fF. The chip includes a temperature sensor offering 0.1°C resolution, a 65b EPROM, and an on-chip charge-pump generating voltages from 8V to 30V to allow sensor self-test using electrostatic actuation. The compensation algorithms and self-test mechanisms explored in this thesis demonstrate a generic approach to microsystem calibration, accuracy, and reliability. The system architecture, power management techniques, sensor bus configuration, and custom circuitry developed address some of the most important remaining challenges for next-generation microsystems and provide a universal prototype for their continued evolution. |
