A switched-capacitor interface for capacitive sensors with wide dynamic range

A novel switched-capacitor interface for capacitive sensors has been developed based on a dual-slope analog-to-digital (A/D) conversion technique. The interface consists of a switched-capacitor integrator, a comparator, and digital circuits. The integrator first samples the sensor capacitance in the form of its proportional charge. A quantized reference charge is then extracted until the output voltage of the integrator becomes zero. An autoranging function is incorporated to achieve a wide dynamic range of sensor capacitance by changing the sampling count in a 2´s geometric manner. A prototype interface built using discrete components has demonstrated a capacitance measurement over four decades with an accuracy better than 1%