A fully-digital, 0.3V, 270 nW capacitive sensor interface without external references

Abstract

This paper presents a fully-digital capacitive sensor interface. By directly transforming the sensor value instead of using an intermediate step in the voltage domain, the architecture can cope with very low signal swings. An implementation for barometric pressure sensing with a supply voltage of 0.3 V demonstrates the benefits. With a power consumption of only 270 nW and an acquisition time of 1 ms, an ENOB of 6.1 is obtained, resulting in a FOM of 2.1 pJ/conv for the entire interface. This is at least an order of magnitude better than current state-of-the-art implementations.