Error analysis of a charge-balancing capacitive sensor interface with resistive reference

This paper presents a detailed error analysis of a charge-balancing capacitive sensor interface (CSI), which is based on resistor-capacitor (R-C) comparison. Precision resistive and time references can be utilized in the CSI to achieve high-precision capacitance-to-digital conversion. However, having precision references is not sufficient for the CSI to perform a precision measurement. The comparison of the measured capacitance with the reference introduces additional errors and instability. As a result, the errors of the comparison circuit degrade the performance of the CSI. For this reason, an in-depth error analysis is performed to identify the error sources and their impacts on the final measurement results. Based on that, error budgets can be properly allocated according to specific requirements. Besides, several circuit techniques are proposed to reduce the corresponding errors. A design example is presented, which achieves a thermal drift as low as 6ppm/°C.