An energy-efficient 15-bit capacitive sensor interface

This paper presents a period-modulator based capacitive sensor interface implemented using energy-efficient building blocks. The integrator in the modulator is based on a current-efficient telescopic OTA, whose limited output swing is accommodated using negative feedback loops. The use of a low-power comparator is enabled by eliminating errors associated with its propagation time using auto-calibration. The interface has been implemented in 0.35 μm standard CMOS technology. Experimental results show that for a capacitance range of 6.8 pF, the interface achieves 15-bit resolution and 12-bit linearity within a measurement time of 7.6 ms, while consuming only 64 μA from a 3.3 V power supply. Compared to previous work with similar performance, this represents a significant improvement in energy efficiency.