Capacitive acceleration sensor system
First Claim
1. An acceleration sensor system comprising:
- a first fixed electrode and a second fixed electrode;
a movable electrode disposed between the first and the second fixed electrodes for providing a first capacitor between the first fixed electrode and the movable electrode and a second capacitor between the second fixed electrode and the movable electrode;
a detection capacitor for detecting a capacitance difference between the first capacitor and the second capacitor;
a charge voltage conversion circuit for outputting and converting a capacitance change of the detection capacitor to an output voltage, the capacitance change being derived from a displacement of the movable electrode caused by an acceleration applied to the sensor;
a detection bias voltage applying means for applying a detection bias voltage between the first fixed electrode and the second fixed electrode;
a vibrating means for vibrating the movable electrode in an acceleration detection direction in such a manner that the movable electrode is displaced in a first period in which the vibrating means applies a displacement bias voltage to the movable electrode, the movable electrode is returned in a second period in which no displacement bias voltage is applied to the movable electrode, and the first and the second periods are repeated alternately;
a sampling means for sampling the output voltage of the charge voltage conversion circuit to detect the acceleration in such a manner that the sampling means selectively samples the output voltage during the second period in a case where the movable electrode is steadily vibrated; and
an acceleration signal generating and outputting means for generating and outputting an acceleration signal on the basis of a sampling result of the output voltage of the charge voltage conversion circuit.
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Accused Products
Abstract
An acceleration sensor system includes: a first and a second fixed electrodes; a movable electrode for providing a first and a second capacitors; a detection capacitor for detecting a capacitance difference between the first and the second capacitors; a charge voltage conversion circuit for converting a capacitance change of the detection capacitor to an output voltage; a detection bias voltage applying means; a vibrating means for vibrating the movable electrode such that a displacement bias voltage is applied in a first period and no displacement bias voltage is applied in a second period; a sampling means for sampling the output voltage during the second period when the movable electrode is stationarily vibrated; and an acceleration signal generating and outputting means for generating an acceleration signal on the basis of a sampling result.
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Citations
13 Claims
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1. An acceleration sensor system comprising:
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a first fixed electrode and a second fixed electrode;
a movable electrode disposed between the first and the second fixed electrodes for providing a first capacitor between the first fixed electrode and the movable electrode and a second capacitor between the second fixed electrode and the movable electrode;
a detection capacitor for detecting a capacitance difference between the first capacitor and the second capacitor;
a charge voltage conversion circuit for outputting and converting a capacitance change of the detection capacitor to an output voltage, the capacitance change being derived from a displacement of the movable electrode caused by an acceleration applied to the sensor;
a detection bias voltage applying means for applying a detection bias voltage between the first fixed electrode and the second fixed electrode;
a vibrating means for vibrating the movable electrode in an acceleration detection direction in such a manner that the movable electrode is displaced in a first period in which the vibrating means applies a displacement bias voltage to the movable electrode, the movable electrode is returned in a second period in which no displacement bias voltage is applied to the movable electrode, and the first and the second periods are repeated alternately;
a sampling means for sampling the output voltage of the charge voltage conversion circuit to detect the acceleration in such a manner that the sampling means selectively samples the output voltage during the second period in a case where the movable electrode is steadily vibrated; and
an acceleration signal generating and outputting means for generating and outputting an acceleration signal on the basis of a sampling result of the output voltage of the charge voltage conversion circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An acceleration sensor system for an automotive vehicle comprising:
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a detection capacitor including a pair of electrodes, which is changeable in accordance with an acceleration applied to the sensor;
an acceleration signal generating circuit including a charge voltage conversion circuit for outputting an acceleration signal;
a memory for memorizing a reference offset output value, which is defined as a reference value of an offset output value of the acceleration signal generating circuit when both ends of the detection capacitor are short-circuited; and
a zero point correcting means, wherein the charge voltage conversion circuit includes an operational amplifier with a negative feedback capacitor for detecting a charge of the detection capacitor, the charge voltage conversion circuit converts a charge output change of the detection capacitor to a voltage change as the acceleration signal, and the zero point correcting means short-circuits both ends of the negative feedback capacitor at a predetermined check time when the sensor is operated, detects the offset output value of the acceleration signal generating circuit as a current offset output value, and corrects a zero point of the acceleration signal on the basis of a comparison between the reference offset output value and the current offset output value. - View Dependent Claims (10, 11, 12, 13)
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Specification