Capacitive physical-quantity detection apparatus

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 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.

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 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.

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 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.