Importance

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Abstract

A balanced charge pump sensor circuit (switched capacitor) for measuring the capacitance of a sensor element includes a switching circuit having a charging state during which the sensing element is connected to a relatively fixed upper reference voltage source. The switching circuit has a discharging state during which the sensing element is connected to a summing node, typically at some different voltage between the upper and lower reference voltages. As a result of this switching action, a packet of charge is transferred from the higher voltage connection to the lower voltage connection, the quantity of charge depending on the voltage difference between these two connections and the capacitance of the sensing element at the time the connections are changed. The circuit includes a current source, a differential amplifier having a non-inverting input terminal and an inverting input terminal, a voltage divider, and a charge integrating capacitor. The balanced charge pump circuit may be used as part of a proximity detection or level measurement system in which the sensor element is positioned within a storage tank to detect or measure the level of fluid or materials stored within the storage tank.

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First Claim