Capacitance-to-Digital Converter for Accurate Displacement Measurement in the Sub-nanometre Range

Roumen Nojdelov, Stoyan Nihtianov, Andrew Yacoot, Dirk Voigt

Abstract

This paper presents a capacitance-to-digital converter (CDC) for accurate displacement measurement in the sub-nanometer range. It is intended for applications in metrology, as part of the efforts to create a new transfer standard for length. The main targeted performance characteristics of the CDC are: stability and resolution. Compared with previously reported works, the CDC is optimized with respect to the dynamic range while dissipating only 45 mW of electric power in proximity to the sensor area. The implemented conversion principle uses one resistor, resistance ratio and time as references, thus achieving a good initial accuracy and a very high stability over temperature and time. The interface is realized at PCB level with off-the-shelf components, and measures up to six sensors sequentially. The capacitance measurement range is 9 pF with an option for 18 pF and 32 pF. The resolution of the converter for 9 pF range is 60 aF (~17 bits dynamic range) with less than 2 ms conversion time.

Keywords

capacitive sensor, capacitance measurement, capacitance-to-digital converter, multislope converter, stability

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IMEKO TC

TC4 - Measurement of Electrical Quantities

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