Sensor circuit for detection of an abnormal offset voltage

• US 7,466,119 B2
• Filed: 08/08/2006
• Issued: 12/16/2008
• Est. Priority Date: 08/22/2005
• Status: Expired due to Fees

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Mase, Shunji, Ito, Hajime, Tsuruhara, Takao
• Primary Examiner(s): Gutierrez; Diego
• Assistant Examiner(s): NATALINI, JEFF WILLIAM
• Application Number:
  US11/500,303
• Publication Number:
  US 20070041135A1
• Time in Patent Office: 861 Days
• Field of Search: 324/76.13
• US Class Current: 324/76.13
• CPC Class Codes: G01C 19/5726 Signal processing
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719
• CPC Class Codes: G01D 3/08 with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A sensor circuit includes an AC component pickup circuit and first and second adder circuits or first and second high-pass filters, and specifies a range of normal voltages by an upper-limit voltage formed by adding an upper-limit threshold value to the AC component in the input voltage and by a lower-limit voltage formed by adding a lower-limit threshold value to the AC component in the input voltage. An abnormal offset voltage is detected by judging whether the output voltage of an inverting amplifier circuit is lying in the range of normal voltages.

Claims

1. A sensor circuit comprising:

sensing means that produces detection signals;

voltage conversion means that subjects the detection signals to voltage conversion to produce a conversion voltage;

AC component pickup means that receives the conversion voltage and picks up an AC component in the conversion voltage;

first adder means that provides an upper-limit voltage by adding an upper-limit threshold value to the AC component;

second adder means that provides a lower-limit voltage by adding a lower-limit threshold value smaller than the upper-limit threshold value to the AC component; and

detecting means that detects an abnormal offset voltage depending upon whether the conversion voltage is in a range of normal voltages between the upper-limit voltage and the lower-limit voltage, wherein

the AC component pickup means and the first adder means form a first high-pass filter,

the AC component pickup means and the second adder means form a second high-pass filter,

the first and second high-pass filters include, respectively first operational amplifiers, first capacitors connected between terminals for receiving the conversion voltage and inverting input terminals of the first operational amplifiers, second capacitors connected between output terminals of the first operational amplifiers and the inverting input terminals of the first operational amplifiers, and first and second resistors connected in parallel with the second capacitors, so that phases of the AC component are inverted,

the conversion voltage is input to the inverting input terminals of the first operational amplifiers via the first capacitors, and the upper-limit threshold value or the lower-limit threshold value is input to the non-inverting input terminals of the first operational amplifiers,

an inverting amplifier is provided between the voltage converting means and the first and second high-pass filters for amplifying the conversion voltage in an inverted manner, and

an inverted voltage is applied to the detecting means to be compared with the upper-limit voltage and the lower-limit voltage.

2. The sensor circuit according to claim 1, wherein the voltage conversion means includes:

first and second voltage conversion means that subjects the detection signals to first and second voltages; and

differential amplifier means that takes a differential in the first and second voltages to produce a differential voltage as the conversion voltage.

3. The sensor circuit according to claim 1, wherein:

the first and second high-pass filters both include, respectively, third resistors connected between the first resistors and the second resistors, and second operational amplifiers that constitute buffer circuits; and

the upper-limit threshold value or the lower-limit threshold value is input to non-inverting input terminals of the second operational amplifiers, so that the upper-limit threshold value or the lower-limit threshold value is output as an output of the buffer circuits, and the output is input to non-inverting input terminals of the first operational amplifiers as well as to the third resistors.

4. The sensor circuit according to claim 1, wherein:

the first and second high-pass filters further includes, respectively, third capacitors that apply predetermined voltages between the first resistors and the second resistors therethrough.