A 15-bit ΔΣ Capacitance-to-Digital Converter For Position Sensing with Electrically Floating Targets

This thesis presents a capacitive sensing technique which is suitable for measuring small displacements with one floating target electrode. A capacitive sensor interface, which does not require electrical contact with the target, while demonstrating performance comparable with the state-of-the-art, is proposed. The designed prototype is intended for displacement measurement with a measurement range from 10 µm to 100 µm, and a resolution better than 3 nm.The proposed design implants the sensor capacitor into the input branch of a capacitance-to-digital converter (CDC), which results in a simpler system that saves power and reduces the error sources.The CDC is taped out in the TSMC 0.18 µm CMOS process with Vdd = 1.8 V. The total chip area is 2.3 mm2 of which 0.5 mm2 is occupied by the CDC. In frequency range from DC to 2 kHz, the resolution of the CDC is thermal noise limited, whereas the quantization noise is shaped to higher frequency. After applying a low-pass digital filter with a bandwidth of 1 kHz, the dynamic range is better than 15 bits, corresponding to 3 nm displacement resolution