A 10-Channel, 1.2 µW, Reconfigurable Capacitance-to-Digital Converter for Low-Power, Wearable Healthcare Applications

This paper presents a multi-channel capacitive sensor interface for low-power wearable healthcare applications. The proposed capacitance-to-digital converter (CDC) shares an analog front-end (AFE) and analog-to-digital converter (ADC) among 10 input channels (10 Ch). The architecture allows programmable channel access and duty cycles inactive channels. The CDC avoids operational transconductance amplifiers (OTAs) to improve energy efficiency and features adaptive sensitivity to support the dynamic range of sensors. The CDC measures a change of capacitance (ΔC) of up to 5.34 pF for 1x sensitivity and up to 1.8 pF for 3x sensitivity, chosen to match the target sensors with on-chip offset correction and sensor baseline calibration. The total power consumption is 1.2 µW for 1.6 kHz sampling frequency (f
s
) when driven by a 32 kHz clock. The energy per conversion is 28.57 pJ at the maximum f
s
of 5.6 kHz. The proposed architecture achieves a 4.6x reduction in power/channel and an 8.6x reduction in energy per conversion compared to prior works. Implemented in 65 nm CMOS process, the 10-channel CDC occupies 0.251 mm
²
of active area (0.0251 mm
²
/Ch).