CMOS differential-capacitance-to-frequency converter utilising repetitive charge integration and charge conservation

A low-complexity CMOS circuit is proposed for reading out monolithically integrated differential capacitive sensors. It directly converts the differential capacitance of a MEMS sensing device to a frequency by accumulating the charges produced by repeated charge integration and charge conservation. A prototype chip has been designed and fabricated in 0.35 m CMOS technology. Experimental results show that differential capacitance is linearly converted to output frequency.