A smart sensing microsystem with a capacitive sensor interface

This paper describes a smart microsystem that utilizes a generic interface circuit capable of interfacing with a large variety of capacitive sensors. This wireless microsystem includes a microcontroller for signal processing, sensors that measure temperature, pressure, humidity, and acceleration, and a 315 MHz transmitter for data output. An interface chip handles communication between the microcontroller and the sensors over a standard sensor bus and provides readout circuitry for the capacitive transducers. This interface circuit is highly programmable, can interface with up to six external sensors, supports sensor self-test, and includes three programmable internal reference capacitors in the range of 0.2-12 pF and a temperature sensor. The chip dissipates less than 2.2 mW from a single 5 V supply and can resolve input capacitance variation better than 1 fF.