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Capacitance detection circuit including voltage compensation function

  • US 7,652,486 B2
  • Filed: 01/17/2008
  • Issued: 01/26/2010
  • Est. Priority Date: 01/17/2008
  • Status: Expired due to Fees
First Claim
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1. A capacitance detection circuit for detecting a capacitance change value of a sensor element, the capacitance detection circuit comprising:

  • a C-V circuit, connected to the sensor element, for amplifying the capacitance change value of the sensor element by a predetermined gain based on a reference voltage to generate a detection signal; and

    a voltage compensation circuit, connected to the C-V circuit, for supplying the reference voltage to the C-V circuit, wherein when the reference voltage fluctuates by a predetermined deviation amount, the voltage compensation circuit reduces the gain relative to the deviation amount;

    wherein the C-V circuit includes;

    an operational amplifier having a first input terminal connected to the sensor element, a second input terminal connected to the voltage compensation circuit, and an output terminal that outputs the detection signal; and

    a feedback capacitor connected between the first input terminal and output terminal of the operational amplifier;

    the sensor element includes;

    a first variable capacitor having a movable electrode connected to the first input terminal of the operational amplifier and a fixed electrode that receives a first drive signal;

    a second variable capacitor having a movable electrode connected to the movable electrode of the first variable capacitor and a fixed electrode that receives a second drive signal; and

    a parasitic capacitor element formed in the sensor element and functioning as a parasitic capacitor connected to the first input terminal of the operational amplifier;

    wherein the sensor element and feedback capacitor set a first load capacitance applied to the first input terminal of the operational amplifier; and

    the voltage compensation circuit includes a plurality of balance capacitors that set a second load capacitance, which is applied to the second input terminal of the operational amplifier, to substantially the same value as the first load capacitance;

    wherein the plurality of balance capacitors include;

    a first balance capacitor having a first electrode, which is connected to the second input terminal of the operational amplifier, and a second electrode, which receives the first drive signal;

    a second balance capacitor having a first electrode, which is connected to the first electrode of the first balance capacitor, and a second electrode, which receives the second drive signal;

    a third balance capacitor having a first electrode, which is connected to the second input terminal of the operational amplifier, and a second electrode, which receives the reference voltage; and

    a fourth balance capacitor having a first electrode, which is connected to the second input terminal of the operational amplifier, and a second electrode, which is connected to the second electrode of the third balance capacitor.

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