A Precise Capacitance-to-Pulse Width Converter for Integrated Sensors

This work describes a novel approach for interfacing capacitive sensors in the sub-pF range. The system generates a PWM signal with a linear relationship between the pulse duration and the sensor capacitance. The circuit exhibits intrinsic low sensitivity to temperature and process variations and is therefore an interesting solution when extremely wide operating temperature ranges are required. A detailed analysis of the noise characteristics, aimed to give indications about the circuit optimisation, is presented. The interface has been designed using the 0.35 μm BCD6 process of STMicroelectronics and tested by means of electrical simulations.