Differential capacitance sampler
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United States of America Patent
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Apr 2, 2002
Grant Date -
N/A
app pub date -
Dec 21, 1999
filing date -
Dec 21, 1999
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
Differential capacitance is sensed by charging two capacitors to a voltage equal in magnitude but opposite in polarity during a short sampling period and discharging them in parallel during the remaining longer period of a pulse repetition cycle. In the preferred embodiment, an operational amplifier converts the charge difference to a voltage output signal. In an embodiment suitable for transducers, high sensitivity and low noise performance is obtained because of the output signal provided by the sensor is directly proportional to the excitation voltage, the excitation frequency and the value of a feedback resistor. This embodiment is also useful for proximity sensing in the presence of moisture and other ionic conductors, because the charging pulse can be of a short duration, typically 100 ns or less. An alternate embodiment, having a sensitivity that is independent of excitation frequency, provides a voltage output signal that is linearly related to the displacement of the central plate of a three-plate capacitor.
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