Capacitive physical quantity sensor

• US 6,483,322 B2
• Filed: 07/11/2001
• Issued: 11/19/2002
• Est. Priority Date: 07/25/2000
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Aoyama, Seiki, Yamauchi, Shigenori
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): Nguyen, Vincent Q.
• Application Number:
  US09/901,606
• Publication Number:
  US 20020011108A1
• Time in Patent Office: 496 Days
• Field of Search: 324/160, 324/162, 324/163, 324/168, 324/661, 324/679, 324/672, 735/143.2, 73/13.8, 327/94, 327/96, 327/337, 327/344
• US Class Current: 324/661
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

The clock signal for the sample and hold circuit for sampling the C-V conversion circuit output generated by the control signal generation circuit is different in period from the clock signal for switched capacitor filter circuit for filtering the sample and hold circuit output such that the clock signal for the switched capacitor filter circuit is unchanged in period between the measuring and self-diagnostic modes.

Claims

1. A capacitive physical quantity sensor comprising:

first and second variable capacitors, each including a movable electrode and a fixed electrode facing each other, capacitances of said first and second variable capacitors varying in accordance with a physical quantity on said movable electrodes;

signal generation means for periodically supplying carrier signals to said fixed electrodes to measure variation in differential capacitance of said first and second variable capacitors at a first period in a measuring mode and at a second period in a self-diagnostic modes and generating a displacement signal for displacing said movable electrodes at said second period in said self-diagnostic mode; and

a signal processing circuit including;

a C-V conversion circuit for converting a charge signal indicative of said differential capacitance into a voltage signal; and

a switched capacitor filter circuit for filtering said voltage signal to output a filtered voltage signal in response to a filter circuit clock signal, wherein said signal generation means further generates said filter circuit clock signal in said measuring and self-diagnostic modes at the same period, and said first period is different from said second period.

2. A capacitive physical quantity sensor as claimed in claim 1, wherein said signal generation means includes an oscillator for generating a reference clock signal;

a counter circuit responsive to said reference clock signal for generating said filter circuit clock signal with the same dividing ratio in said measuring and self-diagnostic modes;

a programmable counter circuit responsive to said reference clock signal for generating said sample and hold clock signal, and said carrier signals in said measuring mode and self-diagnostic mode with different dividing ratios, respectively.

3. A capacitive physical quantity sensor as claimed in claim 1, wherein said signal processing circuit further comprises a sample and hold circuit for sampling and holding said voltage signal in response to a sample and holding clock signal which is different in period from said filter circuit clock signal.

4. A capacitive physical quantity sensor as claimed in claim 3, wherein said signal generation means further generates said sampling and holding clock signal and said filter circuit clock signal and further includes synchronizing means for synchronously outputting said sampling and holding clock signal and said filter circuit clock signal.

5. A capacitive physical quantity sensor as claimed in claim 4, wherein said signal generation means includes a programmable counter circuit for generating said carrier signals and said sampling and holding clock signal at said first period and said second period in said measuring and self-diagnostic modes, respectively.

6. A capacitive physical quantity sensor as claimed in claim 1, wherein said signal processing circuit further comprises a sample and hold circuit for sampling and holding said voltage signal in response to a sample and holding clock signal of which period is different between said measuring and self-diagnostic modes.

7. A capacitive physical quantity sensor as claimed in claim 6, wherein said signal generation means further generates said sampling and holding clock signal and said filter circuit clock signal and further includes synchronizing means for synchronously outputting said sampling and holding clock signal and said filter circuit clock signal.

8. A capacitive physical quantity sensor as claimed in claim 7, wherein said signal generation means includes a programmable counter circuit for generating said carrier signals and said sampling and holding clock signal at said first period and said second period in said measuring and self-diagnostic modes, respectively.