Apparatus and method for multi-axis capacitive sensing
First Claim
1. A sensing device comprising:
- a micromachined sensor having a movable mass, first and second fixed electrodes of a first differential capacitor, and first and second fixed electrodes of a second differential capacitor, wherein the mass includes a third electrode of the first differential capacitor and a third electrode of the second differential capacitor, and the third electrode of the first differential capacitor is electrically connected to the third electrode of the second differential capacitor;
an amplifier having an input electrically coupled to the third electrode of the first differential capacitor and the third electrode of the second differential capacitor;
a first demodulator having an input electrically coupled to an output of the amplifier;
a second demodulator having an input electrically coupled to the output of the amplifier; and
a control timer electrically coupled to the first demodulator and the second demodulator.
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Accused Products
Abstract
A device for detecting with differential capacitors accelerations in more than one orientation through time-division multiplexing. A micromachined mass is movable along or about any axis in response to a force. The mass forms the common electrode of a set of differential capacitors, wherein the other electrodes of each differential capacitor are fixed. With each differential capacitor, one fixed electrode is set to one voltage and the other fixed electrode is set to a second voltage. The mass is connected to the input of an amplifier and to a switch for connecting the mass to a fixed voltage. The output of the amplifier is coupled to a demodulator for each orientation. A timing circuit activates one demodulator at a time. By toggling the voltages on the fixed electrodes of the differential capacitor corresponding to the active demodulator, the movement of the mass in the orientation corresponding to the active demodulator can be determined.
159 Citations
27 Claims
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1. A sensing device comprising:
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a micromachined sensor having a movable mass, first and second fixed electrodes of a first differential capacitor, and first and second fixed electrodes of a second differential capacitor, wherein the mass includes a third electrode of the first differential capacitor and a third electrode of the second differential capacitor, and the third electrode of the first differential capacitor is electrically connected to the third electrode of the second differential capacitor; an amplifier having an input electrically coupled to the third electrode of the first differential capacitor and the third electrode of the second differential capacitor; a first demodulator having an input electrically coupled to an output of the amplifier; a second demodulator having an input electrically coupled to the output of the amplifier; and a control timer electrically coupled to the first demodulator and the second demodulator. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A circuit for measuring change in capacitance comprising:
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a first differential capacitor having a first electrode, a second electrode, and a third electrode, with the first electrode forming a first capacitor of the first differential capacitor with the second electrode, and the first electrode forming a second capacitor of the first differential capacitor with the third electrode; a second differential capacitor having a first electrode, a second electrode, and a third electrode, with the first electrode forming a first capacitor of the second differential capacitor with the second electrode, and the first electrode forming a second capacitor of the second differential capacitor with the third electrode, and wherein the first electrode of the first differential capacitor is coupled to the first electrode of the second differential capacitor; an amplifier having an input coupled to the first electrode of the first differential capacitor and the first electrode of the second differential capacitor; a first demodulator having an input coupled to an output of the amplifier; a second demodulator having an input coupled to the output of the amplifier; and a control timer coupled to the first demodulator and the second demodulator. - View Dependent Claims (20, 21)
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22. A sensing device comprising:
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a movable mass having a first and a second electrode; a first set of fixed electrodes arranged relative to the first movable mass electrode to form a first differential capacitor; a second set of fixed electrodes arranged relative to the second movable mass electrode to form a second differential capacitor; a sensing circuit coupled to the movable mass to detect a change in capacitance of the first differential capacitor during a first time period and a change in capacitance of the second differential capacitance during a second time period; and wherein the first and second differential capacitors are arranged relative to one another to respond to different force components. - View Dependent Claims (23, 24)
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25. A sensing device comprising:
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a first capacitive structure arranged to change capacitive values in response to a first force component; a second capacitive structure arranged to change capacitive values in response to a second force component; an activation and detection circuit for charging the first capacitive structure and detecting a capacitance value in a first time period and for charging the second capacitive structure and detecting a capacitance value in a second time period that does not overlap with the first period. - View Dependent Claims (26, 27)
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Specification