A sensitive differential capacitance to voltage converter for sensor applications

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    Abstract

    There is a need for capacitance to voltage converters (CVC's) for differential capacitive sensors like pressure sensors and accelerometers which can measure both statically and dynamically. A suitable CVC is described in this paper. The CVC proposed is based on a symmetrical structure containing two half ac bridges, is intrinsically immune to parasitic capacitances and resistances, is capable of detecting capacitance changes from dc up to at least 10 kHz, is able to handle both single and differential capacitances, and can easily be realized with discrete components. Its sensitivity is very high: detectable capacitance changes of the order of 2 ppm of the nominal value (24 aF with respect to a nominal capacitance of 12 pF) result in a measured output voltage of 1.5 mV. However, due to drift the absolute accuracy and resolution of the CVC is limited to 3.5 ppm. A differential accelerometer for biomedical purposes was connected to the CVC and showed a sensitivity of 4 V/g. The measured rms output voltage noise in the frequency range of 2-50 Hz is 750 μV, resulting in a signal to noise ratio of 75 dB at an acceleration of 1 g in the frequency range of 2-50 Hz.
    Original languageUndefined
    Pages (from-to)89-96
    Number of pages8
    JournalIEEE transactions on instrumentation and measurement
    Volume48
    Issue number1
    DOIs
    Publication statusPublished - 1999

    Keywords

    • METIS-111858
    • Accelerometers
    • 2 to 50 Hz
    • IR-61431
    • PSPICE simulation
    • absolute accuracy
    • Transfer function
    • Linearity
    • pressure sensors
    • demodulator circuit
    • differential capacitance to voltage converter
    • differential capacitive sensors
    • half AC bridges
    • high sensitivity
    • discrete components
    • symmetrical structure

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