Capacitive physical quantity detection device

• US 20080191714A1
• Filed: 01/17/2008
• Published: 08/14/2008
• Est. Priority Date: 02/08/2007
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Masuda, Masashi, Hayakawa, Junji
• Granted Patent: US 7,795,881 B2
• Time in Patent Office: Days
• US Class Current: 324/661
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

A capacitive physical quantity detection device comprises: a plurality of capacitive physical quantity sensors, wherein each sensor including: a detection unit having a movable electrode and a fixed electrode; a C-V conversion circuit having a differential amplifier circuit, wherein a first input terminal of the differential amplifier circuit is coupled with the movable electrode, a second input terminal of the differential amplifier circuit inputs a reference voltage and a self-diagnosis voltage therein during a normal operation and a self-diagnosis operation, respectively, and the C-V conversion circuit outputs an output voltage; and a signal processing circuit that performs a signal processing of the output voltage, wherein the reference voltage in each sensor is almost the same, the plurality of sensors performs the self-diagnosis operation simultaneously, the self-diagnosis voltage in one of the sensors is a first self-diagnosis voltage is different from the self-diagnosis voltage in another one of the sensors.

Claims

1. A capacitive physical quantity detection device for detecting physical quantity, comprising:

a plurality of capacitive physical quantity sensors, wherein each capacitive physical quantity sensor performs a self-diagnosis operation and a normal operation, each capacitive physical quantity sensor including;

a detection unit having a movable electrode movable in accordance with the physical quantity and a fixed electrode facing the movable electrode;

a C-V conversion circuit having a differential amplifier circuit, wherein a first input terminal of the differential amplifier circuit is coupled with the movable electrode, a second input terminal of the differential amplifier circuit inputs a reference voltage therein during a period of the normal operation and inputs a self-diagnosis voltage therein during a period of the self-diagnosis operation, the reference voltage is used for detecting a capacitance change between the movable electrode and the fixed electrode, the self-diagnosis voltage is used for performing the self-diagnosis operation, the self-diagnosis voltage is different from the reference voltage, and the C-V conversion circuit outputs an output voltage corresponding to the capacitance change between the movable electrode and the fixed electrode; and

a signal processing circuit that performs a signal processing of the output voltage from the C-V conversion circuit so as to produce a signal corresponding to the physical quantity, wherein

the reference voltage in each capacitive physical quantity sensor is almost the same,

the plurality of capacitive physical quantity sensors performs the self-diagnosis operation simultaneously,

the self-diagnosis voltage in one of the plurality of capacitive physical quantity sensors is a first self-diagnosis voltage,

the self-diagnosis voltage in another one of the plurality of capacitive physical quantity sensors is a second self-diagnosis voltage, and

the first self-diagnosis voltage is different from the second self-diagnosis voltage.

2. The capacitive physical quantity detection device according to claim 1, wherein

the first self-diagnosis voltage is higher than the reference voltage, and

the second self-diagnosis voltage is lower than the reference voltage.

3. The capacitive physical quantity detection device according to claim 1, wherein

a potential difference between the reference voltage and the first self diagnosis voltage is almost equal to a potential difference between the reference voltage and the second self-diagnosis voltage.

4. The capacitive physical quantity detection device according to claim 1, wherein

the first self-diagnosis voltage includes a first self-diagnosis potential and a second self-diagnosis potential,

the one of the plurality of capacitive physical quantity sensors switches between the first self-diagnosis potential and the second self-diagnosis potential at a first timing,

the second self-diagnosis voltage includes a third self-diagnosis potential and a fourth self-diagnosis potential,

the another one of the plurality of capacitive physical quantity sensors switches between the third self-diagnosis potential and the fourth self-diagnosis potential at a second timing, and

the first timing is different from the second timing.

5. The capacitive physical quantity detection device according to claim 4, wherein

the first potential is higher than the reference voltage,

the second potential is lower than the reference voltage,

the third potential is higher than the reference voltage, and

the fourth potential is lower than the reference voltage.

6. The capacitive physical quantity detection device according to claim 1, wherein

the detection unit in the one of the plurality of capacitive physical quantity sensors is disposed on a first semiconductor substrate,

the detection unit in the another of the plurality of capacitive physical quantity sensors is disposed on a second semiconductor substrate, and

the first semiconductor substrate is different from the second semiconductor substrate.

7. The capacitive physical quantity detection device according to claim 1, wherein

the detection unit in the one of the plurality of capacitive physical quantity sensors is disposed on a third semiconductor substrate, and

the detection unit in the another one of the plurality of capacitive physical quantity sensors is disposed on the third semiconductor substrate.

8. The capacitive physical quantity detection device according to claim 1, wherein

a displacement direction of the movable electrode in the one of the plurality of capacitive physical quantity sensors is defined as a first direction,

a displacement direction of the movable electrode in the another one of the plurality of capacitive physical quantity sensors is defined as a second direction, and

the one of the plurality of capacitive physical quantity sensors and the another one of the plurality of capacitive physical quantity sensors are disposed such that the first direction is almost perpendicular to the second direction.

9. The capacitive physical quantity detection device according to claim 1, wherein

the capacitive physical quantity detection device is mounded to a vehicle.

10. The capacitive physical quantity detection device according to claim 1, wherein

the self-diagnosis operation provides a detection of an occurrence of a short.

11. The capacitive physical quantity detection device according to claim 1, wherein

the second input terminal of the differential amplifier circuit is a non-inverting input terminal of the differential amplifier circuit.