Acceleration sensing module with a combined self-test and ground electrode
First Claim
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1. An acceleration sensing module comprising, in combination:
- a detection circuit having a first, second and third signal terminals;
a self-test circuit for providing a self-test signal for placing said accelerometer in a self-test mode; and
a sense element chip comprising,a substrate;
a moveable plate substantially parallel to and above said substrate, said moveable plate mounted to said substrate via a pedestal; and
exactly three electrodes formed upon said substrate and coupled to said detection circuit, said three electrodes consisting of a first electrode and a second electrode, coupled respectively to said first and said second terminals, which each combine with portions of said moveable plate to form measurement capacitors, useable by said detection circuit for determining the presence of an acceleration normal to said substrate, said three electrodes also consisting of a third electrode, coupled to said third terminal, which combines with portions of said moveable plate to form, during said self-test mode, to form a self-test capacitor, useable by said detection circuit to causing flexing of said moveable plate.
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Abstract
A micro-machined accelerometer includes a moveable metal plate, mounted upon a semiconductor substrate. The moveable metal plate includes an aperture which contains a pedestal and at least one torsion bar for connecting the pedestal to the moveable metal plate. Measurement electrodes formed on the semiconductor substrate combine with the metal plate to form measurement capacitors A combined self-test/common electrode provides a dual function of a common electrode during operation of the accelerometer and a testing electrode during a self-test procedure.
37 Citations
11 Claims
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1. An acceleration sensing module comprising, in combination:
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a detection circuit having a first, second and third signal terminals; a self-test circuit for providing a self-test signal for placing said accelerometer in a self-test mode; and a sense element chip comprising, a substrate; a moveable plate substantially parallel to and above said substrate, said moveable plate mounted to said substrate via a pedestal; and exactly three electrodes formed upon said substrate and coupled to said detection circuit, said three electrodes consisting of a first electrode and a second electrode, coupled respectively to said first and said second terminals, which each combine with portions of said moveable plate to form measurement capacitors, useable by said detection circuit for determining the presence of an acceleration normal to said substrate, said three electrodes also consisting of a third electrode, coupled to said third terminal, which combines with portions of said moveable plate to form, during said self-test mode, to form a self-test capacitor, useable by said detection circuit to causing flexing of said moveable plate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An acceleration sensing module comprising:
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a detection circuit operable in a first mode to detect an acceleration force, and in a second mode to test the operability of an accelerometer; said accelerometer comprising; a substrate; a moveable plate held at a fixed electrical potential and substantially parallel to and above said substrate, comprising, an aperture, a pedestal positioned within said aperture, and connected to said substrate; and means for connecting said pedestal to at least one edge of said aperture, to allow said moveable plate to rotate, relative to said substrate, about a flexure axis, in the presence of a force normal to said substrate; a first electrode formed upon said substrate and coupled to said detection circuit to receive an AC voltage during said first mode and said second mode; a second electrode formed upon said substrate at a position opposite of said flexure axis from said first electrode, and coupled to said detection circuit to receive a voltage substantially similar to said AC voltage during said first and said second modes; and a third electrode formed upon said substrate to surround said aperture and extend on at least two opposing sides around said second electrode, said third electrode coupled to said detection circuit and having an electrical potential substantially equal to said fixed electrical potential of said substrate during said first mode, and at a different electrical potential during said second mode to perform a self-test of the accelerometer. - View Dependent Claims (10, 11)
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Specification