System and method for measuring a capacitance by transferring charge from a fixed source
First Claim
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1. A capacitive proximity sensor device, the capacitive proximity sensor device comprising:
- a sensing electrode, the sensing electrode having an associated measurable capacitance that varies with object proximity;
a storage capacitor;
a charging circuit, the charging circuit configured to selectively couple the storage capacitor and to selectively charge the storage capacitor to a predetermined level, thereby storing a set amount of charge on the storage capacitor;
a charge transfer circuit, the charge transfer circuit configured to controllably transfer charge from the storage capacitor to the sensing electrode while measuring voltage on the sensing electrode and, where the charge transfer circuit is configured to cease controllably transferring charge responsive to the measured voltage on the sensing electrode reaching a defined level, with a residual voltage remaining on the storage capacitor after the transfer; and
a measurement circuit coupled to the storage capacitor, the measurement circuit configured to measure the residual voltage remaining on the storage capacitor to determine the measurable capacitance associated with the sensing electrode from the measured residual voltage.
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Abstract
A touch sensor device and method is provided that determines measurable capacitances for object detection. The systems and methods measure capacitance by controllably transferring charge from a storage capacitor, and determining the measurable capacitance by measuring the residual voltage remaining on the storage capacitor after the transfer. The systems and methods thus provide an accurate determination of the measurable capacitance that can be used for object proximity sensing.
24 Citations
22 Claims
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1. A capacitive proximity sensor device, the capacitive proximity sensor device comprising:
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a sensing electrode, the sensing electrode having an associated measurable capacitance that varies with object proximity; a storage capacitor; a charging circuit, the charging circuit configured to selectively couple the storage capacitor and to selectively charge the storage capacitor to a predetermined level, thereby storing a set amount of charge on the storage capacitor; a charge transfer circuit, the charge transfer circuit configured to controllably transfer charge from the storage capacitor to the sensing electrode while measuring voltage on the sensing electrode and, where the charge transfer circuit is configured to cease controllably transferring charge responsive to the measured voltage on the sensing electrode reaching a defined level, with a residual voltage remaining on the storage capacitor after the transfer; and a measurement circuit coupled to the storage capacitor, the measurement circuit configured to measure the residual voltage remaining on the storage capacitor to determine the measurable capacitance associated with the sensing electrode from the measured residual voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A capacitive proximity sensor device, the capacitive proximity sensor device comprising:
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a sensing electrode, the sensing electrode having an associated measurable capacitance that varies with object proximity; a storage capacitor; a charging circuit, the charging circuit configured to selectively couple the storage capacitor and to selectively charge the storage capacitor to a predetermined level, thereby storing a set amount of charge on the storage capacitor; a charge transfer circuit, the charge transfer circuit including a field effect transistor coupled between the sensing electrode and the storage capacitor, the charge transfer circuit further including a comparator coupled to the gate of the field effect transistor, the comparator configured to measure voltage on the sensing electrode by comparing the voltage on the sensing electrode with a reference voltage, the comparator configured to operate the field effect transistor in a saturation mode when the voltage on the sensing electrode is less than the reference voltage such that the charge transfer circuit controllably transfers charge from the storage capacitor to the sensing electrode while the voltage on the sensing electrode is less than the reference voltage, and wherein the comparator is configured to turn off the field effect transistor when the voltage on the sensing electrode is greater than the reference voltage such that the charge transfer circuit ceases controllably transferring charge responsive to the voltage on the sensing electrode reaching the reference voltage, with a residual voltage remaining on the storage capacitor after the transfer; and a measurement circuit coupled to the storage capacitor, the measurement circuit configured to measure the residual voltage remaining on the storage capacitor to determine the measurable capacitance associated with the sensing electrode from the measured residual voltage.
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13. A method for sensing a proximate object, the method comprising the steps of:
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charging a storage capacitor to a predetermined level, thereby storing a set amount of charge on the storage capacitor; controllably transferring charge from the storage capacitor to a sensing electrode having an associated measurable capacitance that varies with object proximity while measuring voltage on the sensing electrode, until the measured voltage on the sensing electrode reaches a defined level, with a residual voltage remaining on the storage capacitor after the transferring; and measuring the residual voltage remaining on the storage capacitor; and determining the measurable capacitance associated with the sensing electrode from the measured residual voltage. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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20. A capacitive proximity sensor device, the capacitive proximity sensor device comprising:
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a plurality of sensing electrodes, the plurality of sensing electrodes each having an associated measurable capacitance that varies with object proximity; a plurality of storage capacitors; a charging circuit, the charging circuit configured to selectively couple the storage capacitor and to selectively charge the plurality of storage capacitors to a predetermined level, thereby storing a set amount of charge on each of the plurality of storage capacitors; a charge transfer circuit, the charge transfer circuit configured to controllably transfer charge from each of the plurality of storage capacitors to an associated sensing electrode in the plurality of sensing electrodes while measuring voltage on the associated sensing electrode and, where the charge transfer circuit is configured to cease controllably transferring charge responsive to the measured voltage on the associated sensing electrode reaching a defined level, with a residual voltage remaining on each storage capacitor after the transfer; and a measurement circuit coupled to the plurality of storage capacitors, the measurement circuit configured to measure the residual voltages remaining on each of the plurality of storage capacitors to determine the measurable capacitance associated with each of the plurality of sensing electrodes from the measured residual voltages, and wherein the measured residual voltages are used by the sensor device to determine positional information regarding an object proximate the plurality of sensing electrodes. - View Dependent Claims (21, 22)
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Specification