Reset switch for a micromachined device
First Claim
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1. A device comprising:
- first and second electrodes for receiving respective first and second periodic signals having equal amplitude, period T, and 180°
out of phase with respect to each other;
a movable electrode between the first and second electrodes, the first, second, and movable electrodes forming a differential capacitor with the first electrode and the movable electrode forming a first capacitor, and the second electrode and the movable electrode forming a second capacitor, the capacitances of the first and second capacitors changing in response to movement by the movable electrode;
a DC voltage source; and
a reset switch having a first port coupled to the DC voltage source, a second port coupled to the movable electrode, and a control port responsive to a reset signal for periodically closing the reset X switch synchronously with the periodic signals so that the DC voltage source resets the DC voltage on the movable electrode when the reset switch is closed.
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Abstract
In a circuit for use with a micromachined device having a movable mass that forms an inner electrode of a differential capacitor, oppositely phased square waves are applied to two outer electrodes of the differential capacitor. A reset voltage is applied to the inner electrode synchronously with the square waves to stabilize and control the potential on the inner electrode. The signal on the inner electrode is demodulated by sampling during a first half of the square wave and a second half of the square wave between applications of the reset pulse to obtain a voltage that does not contain noise due to the reset switch.
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Citations
18 Claims
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1. A device comprising:
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first and second electrodes for receiving respective first and second periodic signals having equal amplitude, period T, and 180°
out of phase with respect to each other;a movable electrode between the first and second electrodes, the first, second, and movable electrodes forming a differential capacitor with the first electrode and the movable electrode forming a first capacitor, and the second electrode and the movable electrode forming a second capacitor, the capacitances of the first and second capacitors changing in response to movement by the movable electrode; a DC voltage source; and a reset switch having a first port coupled to the DC voltage source, a second port coupled to the movable electrode, and a control port responsive to a reset signal for periodically closing the reset X switch synchronously with the periodic signals so that the DC voltage source resets the DC voltage on the movable electrode when the reset switch is closed. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for use with a differential capacitor having first and second outer electrodes, and an inner electrode, the method comprising the steps of:
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(a) receiving, by the first outer electrode a first periodic signal; (b) receiving, by the second outer electrode, a second periodic signal, the second periodic signal having approximately the same minimum voltage, maximum voltage, and period T as the first periodic signal and being approximately 180°
out of phase with respect to the first periodic signal; and(c) receiving by the inner electrode a DC voltage signal to periodically reset the DC voltage of the inner electrode synchronized with the periodic signals. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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15. A method for use with a surface micromachined sensor having a movable mass elongated along a first direction, with fingers extending transverse to the first direction and away from the mass to form movable electrodes, and a plurality of stationary fingers forming first and second groups of fixed electrodes, wherein each movable electrode is between a fixed finger in the first group and a fixed finger in the second group to form a differential capacitor, the method comprising the steps of:
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(a) providing to the first group of fixed electrodes a first periodic signal; (b) providing to the second group of fixed electrodes a second periodic signal, the second periodic signal having approximately the same minimum voltage, maximum voltage, and period T as the first periodic signal and being approximately 180°
out of phase with respect to the first periodic signal; and(c) periodically providing to the movable mass a fixed DC voltage signal to reset a DC voltage of the movable mass when the DC voltage signal is provided, the fixed DC voltage signal being provided so that it is synchronized with the periodic signals. - View Dependent Claims (16, 17, 18)
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Specification