Capacitive physical-quantity detection apparatus
First Claim
1. A capacitive physical-quantity detection apparatus comprising:
- a movable electrode which is displaced in response to a physical quantity;
a fixed electrode opposed to the movable electrode to form a capacitor in conjunction with the movable electrode;
signal applying means for applying a first signal between the movable electrode and the fixed electrode, the first signal being periodic and having at least a first time period corresponding to a normal-operation time period for detection of a capacity variation and a second time period for displacement of the movable electrode to implement self diagnosis;
a C-V conversion circuit for generating a voltage which depends on a variation in a capacitance of the capacitor during the first time period the C-V conversion circuit including a switch for discharging the capacitor to implement a resetting process;
a signal processing circuit for processing the voltage generated by the C-V conversion circuit into a second signal depending on the physical quantity; and
changing means for changing the first signal in the second time period between a state for execution of self diagnosis and a state for unexecution of self diagnosis;
wherein the first signal in the state for execution of self diagnosis applies a pseudo physical quantity to the movable electrode, and the changing means includes means for changing a potential at the movable electrode, and wherein the signal applying means includes means for, during execution of self diagnosis, subjecting the fixed electrode to a potential equal to that applied to the fixed electrode for the normal-operation time period.
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Accused Products
Abstract
A capacitive physical-quantity detection apparatus includes a movable electrode (2d) which is displaced in response to a physical quantity. A fixed electrode (3, 4) opposed to the movable electrode forms a capacitor in conjunction with the movable electrode. A signal applying device (23, 24) operates for applying a first signal between the movable electrode and the fixed electrode. The first signal is periodic, and has at least a first time period for detection of a capacity variation and a second time period for displacement of the movable electrode to implement self diagnosis. A C-V conversion circuit (21) operates for generating a voltage which depends on a variation in a capacitance of the capacitor during the first time period. A signal processing circuit (22) operates for processing the voltage generated by the C-V conversion circuit into a second signal depending on the physical quantity. A changing device (23) operates for changing the first signal in the second time period between a state for execution of self diagnosis and a state for unexecution of self diagnosis. The first signal in the state for execution of self diagnosis applies a pseudo physical quantity to the movable electrode.
174 Citations
20 Claims
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1. A capacitive physical-quantity detection apparatus comprising:
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a movable electrode which is displaced in response to a physical quantity;
a fixed electrode opposed to the movable electrode to form a capacitor in conjunction with the movable electrode;
signal applying means for applying a first signal between the movable electrode and the fixed electrode, the first signal being periodic and having at least a first time period corresponding to a normal-operation time period for detection of a capacity variation and a second time period for displacement of the movable electrode to implement self diagnosis;
a C-V conversion circuit for generating a voltage which depends on a variation in a capacitance of the capacitor during the first time period the C-V conversion circuit including a switch for discharging the capacitor to implement a resetting process;
a signal processing circuit for processing the voltage generated by the C-V conversion circuit into a second signal depending on the physical quantity; and
changing means for changing the first signal in the second time period between a state for execution of self diagnosis and a state for unexecution of self diagnosis;
wherein the first signal in the state for execution of self diagnosis applies a pseudo physical quantity to the movable electrode, and the changing means includes means for changing a potential at the movable electrode, and wherein the signal applying means includes means for, during execution of self diagnosis, subjecting the fixed electrode to a potential equal to that applied to the fixed electrode for the normal-operation time period. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A capacitive physical-quantity detection apparatus comprising:
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a movable electrode which is displaced in response to a physical quantity;
a fixed electrode opposed to the movable electrode to form a capacitor in conjunction with the movable electrode;
signal applying means for applying a first signal between the movable electrode and the fixed electrode, the first signal being periodic and having at least a first time period for detection of a capacity variation and a second time period for displacement of the movable electrode to implement self diagnosis;
a C-V conversion circuit for generating a voltage which depends on a variation in a capacitance of the capacitor during the first time period, the C-V conversion circuit including an amplifying circuit having first and second input terminals, the first input terminal being connected to the movable electrode, the C-V conversion circuit including a switch for discharging the capacitor to implement a resetting process;
reference applying means for applying a reference voltage to the second input terminal of the amplifying circuit;
a signal processing circuit for processing the voltage generated by the C-V conversion circuit into a second signal depending on the physical quantity; and
changing means for changing the first signal in the second time period between a state for execution of self diagnosis and a state for unexecution of self diagnosis;
wherein the first signal in the state for execution of self diagnosis applies a pseudo physical quantity to the movable electrode, and the changing means includes means for changing the reference voltage applied to the second input terminal of the amplifying circuit and thereby changing a potential at the movable electrode. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A capacitive physical-quantity detection apparatus comprising:
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a movable electrode which is displaced in response to a physical quantity;
a fixed electrode opposed to the movable electrode to form a capacitor in conjunction with the movable electrode;
signal applying means for applying a first signal between the movable electrode and the fixed electrode, the first signal being periodic and having at least a first time period for detection of a capacity variation and a second time period for displacement of the movable electrode to implement self diagnosis;
a C-V conversion circuit for generating a voltage which depends on a variation in a capacitance of the capacitor during the first time period, the C-V conversion circuit including a switch for discharging the capacitor to implement a resetting process;
a signal processing circuit for processing the voltage generated by the C-V conversion circuit into a second signal depending on the physical quantity; and
changing means for changing the first signal in the second time period between a state for execution of self diagnosis and a state for unexecution of self diagnosis;
wherein the first signal in the state for execution of self diagnosis applies a pseudo physical quantity to the movable electrode, and the movable electrode and the C-V conversion circuit remain electrically connected with each other during execution of self diagnosis. - View Dependent Claims (15, 16, 17, 18, 19)
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20. A capacitive physical-quantity detection apparatus comprising:
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a movable electrode which is displaced in response to a physical quantity;
a fixed electrode opposed to the movable electrode to form a capacitor in conjunction with the movable electrode;
signal applying means for applying a first signal between the movable electrode and the fixed electrode, the first signal being periodic and having at least a first time period for detection of a capacity variation and a second time period for displacement of the movable electrode to implement self diagnosis;
a C-V conversion circuit for generating a voltage which depends on a variation in a capacitance of the capacitor during the first time period;
a signal processing circuit for processing the voltage generated by the C-V conversion circuit into a second signal depending on the physical quantity; and
changing means for changing the first signal in the second time period between a state for execution of self diagnosis and a state for unexecution of self diagnosis;
wherein the first signal in the state for execution of self diagnosis applies a pseudo physical quantity to the movable electrode, and a frequency of the first signal is higher than a resonance frequency of the movable electrode in a direction of displacement of the movable electrode.
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Specification