Charge transfer capacitive position sensor
First Claim
1. ) A capacitive sensor for providing an output representative of a position along a sensing body extending between two electrodes at which an object is proximate the sensing body, the sensor comprising:
- two capacitive sensing channels, each channel connected to a respective one of the electrodes, each channel having a respective channel output representative of a respective non-linear response to a capacitive load imposed by the object when the object is proximate the body;
means for operating the two channels synchronously, and calculation means for receiving the respective outputs from the two channels, for calculating a ratio of a selected linear combination of the outputs of the two channels, the ratio varying linearly with the position of the object, and for supplying the ratio as the output representative of the position.
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Accused Products
Abstract
The position of an object, which may be a user'"'"'s finger, along a body is sensed capacitively. A measurement circuit meters the simultaneous injection of electrical charge into the two ends of the body, which may be shaped as a straight line or as a curve. A computing device computes the ratio of the relative changes in the amount of charge injected into each end of the element. The result of this computation is a one dimensional coordinate number plus a detection state indication, both of which can be fed to another functional element, such as an appliance controller, which interprets the coordinate and detection state as a command or measurement.
196 Citations
28 Claims
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1. ) A capacitive sensor for providing an output representative of a position along a sensing body extending between two electrodes at which an object is proximate the sensing body, the sensor comprising:
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two capacitive sensing channels, each channel connected to a respective one of the electrodes, each channel having a respective channel output representative of a respective non-linear response to a capacitive load imposed by the object when the object is proximate the body;
means for operating the two channels synchronously, and calculation means for receiving the respective outputs from the two channels, for calculating a ratio of a selected linear combination of the outputs of the two channels, the ratio varying linearly with the position of the object, and for supplying the ratio as the output representative of the position. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. ) A capacitive sensor for sensing a position of an object along a sensing body extending between two electrodes, the sensor comprising:
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two sensing channels respectively connected to the two electrodes, each sensing channel comprising;
a respective sample capacitor having two terminals, one of which is connected to the associated electrode by means not comprising an electric switching element;
three electric switching elements, each of the three switching elements having both a single respective closed state for connecting one of the terminals of the respective sample capacitor only to one of two different reference voltages, each of the respective switching elements further having a respective open state in which it does not connect the respective one of the terminals to either of the two reference voltages; and
a respective measurement circuit for supplying an output responsive to a measurement at a selected one of the terminals of the respective sample capacitor;
a switch controller for selectively opening and closing the switching elements; and
means for calculating the position of the object from the respective outputs of the two measurement circuits. - View Dependent Claims (14, 15, 16, 17)
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18. ) A capacitive sensor for sensing a position of an object along a sensing body extending between two electrodes, the sensor comprising:
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a switch controller for selectively closing ones of a plurality of electric switching elements;
two sensing channels having respective inputs from the electrodes and having respective outputs from respective associated measurement circuits, each of the sensing channels comprising a respective sample capacitor having two terminals, one of which is connected to a respective electrode by means not comprising one of the electric switching elements;
at least one respective electric switching element of the plurality thereof for resetting the respective sample capacitor by connecting both of its terminals to a first selected reference voltage;
at least two additional respective switching elements of the plurality thereof for alternately switching one of the two terminals of the respective sample capacitor to the first selected reference voltage and the second of the two terminals to a second selected reference voltage; and
a means for calculating the position of the object from the respective outputs of the two measurement circuits. - View Dependent Claims (19, 20, 21, 22, 23)
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24. ) A method for measuring a position of an object along a sensing body extending between two electrodes, each of the two electrodes connected to a respective capacitive sensing channel, each of channels comprising a respective sample capacitor having one of its two terminals connected to a respective one of the two electrodes, each of the channels further comprising a respective measurement circuit having a respective output, the respective measurement circuit connected to a selected one of the two terminals of the respective sample capacitor, the method comprising the sequentially executed steps of:
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a) resetting each of the sample capacitors to a respective selected initial state;
b) simultaneously closing respective first switches, each of the first switches respectively associated with only one of the channels, to connect the respective selected terminal of each sample capacitor to a first selected voltage;
d) waiting a selected interval, and then simultaneously opening both of the first switches;
e) closing respective second switches to connect each of the terminals of the respective sample capacitors that is not the respective selected terminal to a respective second selected voltage;
f) measuring, for each channel, by means of the respective measurement circuit, a respective voltage at the respective selected terminal of the respective sample capacitor; and
g) calculating, from the outputs of the two measurement circuits, the position of the object. - View Dependent Claims (25, 26, 27, 28)
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Specification