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

A low-power and high-accuracy switched-capacitor (SC) capacitance-to-time (C/T) converter used as an interface for differential capacitive sensors is presented. The propagation delays of the comparator do not directly have effect on the accuracy, but the difference between rising propagation delays of the comparator for two reference voltages does. Lower power consumption can be attained without causing the reduction of conversion accuracy, because of the design constraints on the operational speed of a comparator can be relaxed. Performances of the proposed circuit are simulated by HSPICE using 0.18 micrometers CMOS process parameters. Simulated results have demonstrated that the gain error is 0.0087 % and the maximum nonlinear error is 0.027 % of the full scale. The power consumption of the proposed circuits is 25.6 microwatts for 1.8 V supply voltage. The proposed circuit is suited for co-integration with MEMS-type sensors and microcontroller-based measurement system.