초록 ▼

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 dischargin

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.

대표청구항 ▼

1. A balanced charge pump circuit for coupling to a capacitive sensor element through a switching circuit for measuring the capacitance of the sensor element, wherein the switching circuit has a charging state for coupling the capacitive sensor element to an upper reference voltage source to charge

1. A balanced charge pump circuit for coupling to a capacitive sensor element through a switching circuit for measuring the capacitance of the sensor element, wherein the switching circuit has a charging state for coupling the capacitive sensor element to an upper reference voltage source to charge the sensor element to a predetermined voltage and a discharging state in which a discharge current representative of the capacitance of the sensor element is transferred through the switching circuit, the switching circuit cycling between its charging and discharging states, the balanced charge pump circuit comprising:a summing node coupled to the sensor element to receive discharge current when the switching circuit is in its discharging state; a current source having a first terminal coupled to the summing node and a second terminal coupled to a lower reference voltage source for generating a source current when the summing node is coupled to the sensor element to drain current from the summing node and to offset the amount of discharge current otherwise flowing through the summing node; a differential amplifier having a non-inverting input terminal and a inverting input terminal, wherein the inverting input terminal is coupled to the summing node, the differential amplifier generating a voltage differential signal at an output terminal representative of the discharge current from, and the capacitance of, the sensor element; and a voltage divider coupled to the non-inverting input terminal of the differential amplifier that maintains the voltage at the non-inverting input terminal equivalent to a proportion of the voltage of the upper reference voltage source; wherein the balanced charge pump circuit discharges the sensor element when the sensor element is decoupled from the upper reference voltage source and generates the voltage differential signal representative of the capacitance of the sensor element.