High-Accuracy, Low-Power Switched-Capacitor Differential-Capacitance-to-Time Converter

摘要

A high-accuracy switched-capacitor (SC) capacitance-to-time (C/T) converter for differential capacitive sensors is presented. In the proposed circuit the propagation delays and the offset voltage of the comparator, the finite gain of the op-amp, and the channel charge injection and clock feedthrough due to analog switches have negligible effect on the accuracy of the circuit. Therefore, the design constraints of op-amp and comparator can be relaxed even for high conversion accuracy. Performances of the proposed circuit are simulated using 0.18 micrometers CMOS process parameters. Simulated results have demonstrated that the gain error is 0.0035 % and the maximum nonlinear error is about 0.015 % of the full scale and indicate that 0.1% resolution is achievable even when low-gain amplifier is used. The power consumption of the proposed circuits was 41.3 microwatts for ± 0.9 V supply voltages.