Capacitive physical quantity detection device

• US 6,450,029 B1
• Filed: 09/22/2000
• Issued: 09/17/2002
• Est. Priority Date: 09/27/1999
• Status: Expired due to Term

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Sakai, Minekazu, Yoshihara, Shinji
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): SAINT SURIN, JACQUES M
• Application Number:
  US09/667,800
• Time in Patent Office: 725 Days
• Field of Search: 734/88, 736/52, 735/141.8, 735/143.2, 735/141.6, 738/626.1, 73/13.8, 324/661, 324/672, 324/678, 324/686, 324/162, 361/280, 361/283.1, 361/283.3
• US Class Current: 73/488
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type

Abstract

A capacitive semiconductor acceleration sensor capable of efficiently performing a self-diagnostic procedure without having to provide any separate electrodes for self-diagnosis purposes. The acceleration sensor includes a beam portion that is deformable upon application of acceleration thereto in a direction at right angles to the elongate direction thereof to thereby exhibit a spring function. The sensor also includes a movable electrode and fixed electrodes which are integrally formed with the beam portion. The sensor is operable to detect the acceleration while applying between the movable electrode and fixed electrodes a periodically changeable signal to derive an output voltage variable in potential with a differential capacitance change of capacitors between the both electrodes. Here, a detection signal for detection of such acceleration and a self-diagnosis signal are selectively applied while permitting creation of quasi-acceleration at the movable electrode due to application of the self-diagnosis signal, wherein a ratio of a frequency of the self-diagnosis signal to a resonance frequency of the beam portion in its deformation direction is set so that the resultant resonance magnification of such beam portion is more than or equal to one time upon application of the self-diagnosis signal.

Claims

1. A capacitive physical quantity detection device comprising:

a spring portion deformable upon application of a physical quantity in a specified direction to thereby have a spring function;

a movable electrode integrally formed with the spring portion and deformable along with the spring portion in a deformation direction of the spring portion;

a fixed electrode disposed opposing the movable electrode;

signal application means connected to the movable portion and the fixed portion, for selectively applying between the movable electrode and the fixed electrode any one of periodically changeable signals including a detection signal for detection of the physical quantity and a self-diagnosis signal for use in performing self-diagnosis; and

a C-V conversion circuit for generating an output voltage pursuant to a change in a capacitive element defined between the movable electrode and the fixed electrode,

wherein the capacitive element is changeable in capacitance during application of the detection signal to thereby permit detection of the physical quantity;

the spring portion is deformable upon application of the self-diagnosis signal to permit creation of a quasi-physical quantity at the movable electrode; and

a ratio of a frequency of the self-diagnosis signal to a resonance frequency of the spring portion in its deformation direction is set so that a resonance magnification of the spring portion is more than or equal to one time upon applying of the self-diagnosis signal.

2. A capacitive physical quantity detection device according to claim 1, wherein the ratio of the frequency of the self-diagnosis signal to the resonance frequency of the spring portion in its deformation direction being set so that resonance magnification is 1.1 times or greater upon applying of the self-diagnosis signal.

3. A capacitive physical quantity detection device comprising:

a spring portion deformable upon application of a physical quantity in a specified direction to thereby have a spring function;

a movable electrode integrally formed with this spring portion and deformable along with the spring portion in a deformation direction of the spring portion;

a fixed electrode disposed opposing the movable electrode;

signal application means connected to the movable portion and the fixed portion, for selectively applying between the movable electrode and the fixed electrode any one of periodically changeable signals including a detection signal for detection of the physical quantity and a self-diagnosis signal for use in performing self-diagnosis; and

a C-V conversion circuit for generating an output voltage pursuant to a change in a capacitive element defined between the movable electrode and the fixed electrode,

wherein the capacitive element is changeable in capacitance during application of the detection signal to thereby permit detection of the physical quantity;

the spring portion is deformable upon application of the self-diagnosis signal to permit creation of a quasi-physical quantity at the movable electrode; and

the self-diagnosis signal having a frequency less than or equal to a specified value that is 1.41 times of a resonance frequency of the spring portion in a deformation direction thereof.

4. A capacitive physical quantity detection device according to claim 3, wherein the frequency of the self-diagnosis signal ranges from 0.2 to 1.4 times of the resonance frequency of the spring portion in the deformation direction thereof.

5. A capacitive physical quantity detection device comprising:

a spring portion deformable upon application of a physical quantity in a specified direction to thereby have a spring function;

a movable electrode integrally formed with the spring portion and deformable along with the spring portion in a deformation direction of the spring portion;

a fixed electrode disposed opposing the movable electrode;

signal application means connected to the movable portion and the fixed portion, for selectively applying between the movable electrode and the fixed electrode any one of periodically changeable signals including a detection signal for detection of the physical quantity and a self-diagnosis signal for use in performing self-diagnosis; and

a C-V conversion circuit for generating an output voltage pursuant to a change in a capacitive element defined between the movable electrode and the fixed electrode,

wherein the capacitive element is changeable in capacitance during application of the detection signal to thereby permit detection of the physical quantity;

the spring portion is deformable upon application of the self-diagnosis signal to permit creation of a quasi-physical quantity at the movable electrode; and

a ratio of a frequency of the self-diagnosis signal to a resonance frequency of the spring portion in its deformation direction being set to cause the spring portion to vibrate upon application of the self-diagnosis signal.

6. A capacitive physical quantity detection device comprising:

a beam portion deformable upon application of a physical quantity in a direction substantially at right angles to an elongate direction of the beam portion;

a movable electrode being integrally formed with the beam portion into a beam-like shape extending in the same direction as the elongate direction of the beam portion and being deformable along with the beam portion in a deformation direction of the beam portion;

a fixed electrode disposed opposing the movable electrode;

signal application means connected to the movable portion and the fixed portion, for selectively applying between the movable electrode and the fixed electrode any one of periodically changeable signals including a detection signal for detection of the physical quantity and a self-diagnosis signal for use in performing self-diagnosis;

a C-V conversion circuit for generating an output voltage pursuant to a change in a capacitive element defined between the movable electrode and the fixed electrode,

wherein the capacitive element is changeable in capacitance during application of the detection signal to thereby permit detection of the physical quantity;

the beam portion is deformable upon application of the self-diagnosis signal to permit creation of a quasi-physical quantity at the movable electrode; and

a beam width at the beam portion in the deformation direction thereof being substantially identical to a beam width at the beam portion in its deformation direction while letting stiffness at the movable electrode in its deformation direction be greater than stiffness at the beam portion in the deformation direction thereof.

7. A capacitive physical quantity detection device according to claim 6, wherein the beam width at the movable electrode in its deformation direction ranges from 0.8 to 1.2 times of the beam width at the beam portion in the deformation direction thereof.

8. A capacitive physical quantity detection device according to claim 6, wherein:

the fixed electrode is elongated in substantially parallel to the movable electrode,

the movable electrode and the fixed electrode oppose each other at a side face of the beam portion,

herein the beam width of the fixed electrode in the deformation direction of the beam portion is substantially identical to the beam width at the movable electrode in its deformation direction.