A time/resistor-referenced capacitive sensor interface for displacement measurement in the sub-nanometer range

This work presents a precision capacitive-sensor interface (CSI) designed for displacement measurement in the (sub)nanometer range. It digitizes a capacitance in the 8–12 pF range, corresponding to 4μm displacement range, with 12-bit resolution (150 pm) and excellent stability: thermal drift below 10ppm/^oC in the temperature range from 20°C to 70°C. The conversion time is 10ms while the power consumption is only 660μW. The CSI is particularly suited for applications in which periodic calibration is not possible. For instance, position sensing in high precision industrial systems, such as lithographic machines, where the position of critical mechanical components needs to be measured with sub-nanometer precision.