Capacitance to Digital Converter

This paper presents a Capacitance to Digital Converter (CDC) with a fast serial digital output. The CDC is intended to be used as a flexible solution for interfacing multiple capacitive sensors with maximum value 1nF. A cable capacitance of up to 1nF can be tolerated. Two different modes of measurement are available -a normal mode and a fast mode. The conversion time is 39μs and 64μs for the fast and the normal mode, respectively. The resolution in normal mode, with cable capacitance less than 400pF, is better than 14 bits. A special multi-slope A-to-D conversion is used, which at the beginning and at the end of the conversion process transforms itself into sigma/delta conversion. The interface is realized on a PCB with a Single Euro-board format. Six sensors can be interfaced in programmable sequence. The power consumption is less than 1W.