A high-accuracy differential-capacitance-to-time converter for capacitive sensors

A high-accuracy switched-capacitor (SC) differential-capacitance-to-time converter (DCTC) for capacitive sensors is presented for high-accuracy ratiometric operation. This circuit does not require component matching. Performances of the proposed circuit are simulated by HSPICE using 0.18 μm CMOS process parameters. Simulated results have demonstrated that 0.2% resolution is achievable. The op-amp and comparator were integrated using 0.18 μm triple-well CMOS process. Measured results using prototype circuits indicate that the gain and offset errors are 0.16% and 0.095% of the full scale, respectively. The proposed circuit is suited for co-integration with MEMS-type sensors and microcontroller-based measurement system.