Highly stable capacitance-to-digital converter with improved dynamic range

This paper presents the design, implementation and verification of a highly stable capacitance-to-digital converter (CDC). This converter is based on a multi-slope type of converter which utilizes stable resistors as reference components. Based on the previous works, a so-called “zoom-in” technique is applied in this design which significantly improves the dynamic range of the converter. The measurement range is up to 100pF if the zoom-in is enabled. Depending on the measurement mode, the measurement time varies from 51us to 75us. The experimental results show that the converter achieves up to 18.5-bit dynamic range when enabling the zoom-in and 3.6 ppm/°C temperature stability. The 1/f noise corner of the converter is around 20mHz which indicates good long-term stability.