Electric field attraction minimization circuit
First Claim
1. A sensor comprising:
- a sensing differential capacitor having a first sense electrode, a second sense electrode, and a third sense electrode, with the third sense electrode forming a first sense capacitor of the sensing differential capacitor with the first sense electrode and a second sense capacitor of the sensing differential capacitor with the second sense electrode, and with the capacitances of the first sense capacitor and the second sense capacitor being variable in response to a force applied to the sensor;
means for coupling the first sense electrode to a first carder signal and the second sense electrode to a second carrier signal of the same frequency, with the first carder signal being 180 degrees out of phase with the second carrier signal;
a buffer having an input coupled to the third sense electrode; and
a low-pass filter coupled to the first sense electrode, the second sense electrode, and the output of the buffer, so that the filter is disposed between the first sense electrode and the output of the buffer and between the second sense electrode and the output of the buffer.
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Accused Products
Abstract
A circuit for minimizing electrostatic forces in capacitance-based sensor circuits. A sensor includes a movable mass that forms the center electrode of two differential capacitors, a sensing differential capacitor and an actuator differential capacitor. The other two electrodes of each differential capacitor are fixed. Oppositely phased high-frequency carrier signals are applied to the fixed electrodes of the sensing capacitor and biasing signals are applied to the fixed electrodes of the actuator capacitor. When a force is applied to the sensor, the capacitance of the sensing capacitor changes and the carrier signal, with its amplitude and phase modulated in accordance with the magnitude and direction of the force, appears on the movable mass. The signal on the mass is fed back to the fixed electrodes of the sensing capacitor to minimize electrostatic forces between the electrodes of the sensing capacitor. Using a separate negative feedback loop, a signal is fed back to the mass to generate electrostatic forces between the mass and the fixed electrodes of the actuator capacitor to restore the mass to its original position.
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Citations
16 Claims
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1. A sensor comprising:
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a sensing differential capacitor having a first sense electrode, a second sense electrode, and a third sense electrode, with the third sense electrode forming a first sense capacitor of the sensing differential capacitor with the first sense electrode and a second sense capacitor of the sensing differential capacitor with the second sense electrode, and with the capacitances of the first sense capacitor and the second sense capacitor being variable in response to a force applied to the sensor; means for coupling the first sense electrode to a first carder signal and the second sense electrode to a second carrier signal of the same frequency, with the first carder signal being 180 degrees out of phase with the second carrier signal; a buffer having an input coupled to the third sense electrode; and a low-pass filter coupled to the first sense electrode, the second sense electrode, and the output of the buffer, so that the filter is disposed between the first sense electrode and the output of the buffer and between the second sense electrode and the output of the buffer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A sensor comprising:
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a differential capacitor having a first electrode, a second electrode, and a third electrode, with the third electrode forming a first capacitor of the differential capacitor with the first electrode and a second capacitor of the differential capacitor with the second electrode, and with the capacitances of the first capacitor and the second capacitor being variable in response to a force applied to the sensor; first coupling means for coupling the first electrode to a first carrier signal and the second electrode to a second carrier signal of the same frequency as the first carrier signal, with the first carrier signal being 180 degrees out of phase with the second carrier signal; a buffer having an input coupled to the third electrode; a demodulator having an input coupled to an output of the buffer; a low-pass filter coupled to the first electrode and the second electrode; and second coupling means for coupling the filter to an output of the demodulator, with the filter being disposed between the first electrode and the second coupling means and between the second electrode and the second coupling means. - View Dependent Claims (15, 16)
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Specification