Low-noise 16-bit First-order Delta-sigma Capacitance-to-digital Converter for Capacitive Humidity Sensor

In this paper, a low-noise 16-bit capacitance-to-digital convertor (CDC) for a capacitive humidity sensor is proposed. The proposed sensor interface circuit is implemented as a first-order incremental delta-sigma structure and directly converts the capacitance change of the humidity sensor to a 16-bit digital code. A switched capacitor (SC) integrator of the delta-sigma modulator is adopted in the chopper stabilization technique for a low-noise characteristic. The chopper stabilization technique can avoid the offset and low-frequency flicker noise of an amplifier. The offset cancellation programmable capacitor array of the input stage is used for eliminating the mismatched capacitance from the parasitic capacitor and process variations. The proposed delta-sigma CDC has an accumulator with a simple 16-bit dual counter that converts the delta-sigma modulator output to a 16-bit digital code for reducing the power consumption of the back-end digital processing. The proposed sensor interface circuit is fabricated using the standard 0.18 μm complementary metal-oxide-semiconductor process with an active area of 0.66 mm². The effective resolution of the worst case is 14.4 bits, and the active power consumption of the proposed delta-sigma CDC is 376 μW with a 1.8 V supply.