Capacitance detection circuit and capacitance detection method
First Claim
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1. A capacitance detection circuit, comprising:
- a first buffer amplifier, wherein an input of said first buffer amplifier is connected to a capacitor to be detected by a signal wire;
a first diode and a second diode, connected in series, the anode of the first diode connected to the cathode of the second diode at a first junction point, and the anode of the second diode connected to the signal wire, and the cathode of the first diode connected to a first power supply;
a third diode and a fourth diode, connected in series, the anode of the third diode connected to the cathode of the fourth diode at a second junction point, and the cathode of the third diode connected to the signal wire, and the anode of the fourth diode connected to a second power supply;
wherein;
an output terminal of the first buffer amplifier is connected to the first junction point of the first diode and the second diode via a first capacitance;
said output terminal of the first buffer amplifier is connected to the second junction point of the third diode and the fourth diode via a second capacitance;
the first junction point is connected to a point having a voltage whose value is between the voltage of the first power supply, and the voltage of the signal wire, via a first resistor;
the second junction point is connected to a point having a voltage whose value is between the voltage of the second power supply and the voltage of the signal wire, via a second resistor.
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Abstract
A capacitance detection circuit containing an input protection circuit and having high sensitivity is provided. A capacitance detection circuit for detecting the capacitance of a capacitive sensor, comprising a buffer amplifier connected to the capacitive sensor via a signal wire and having a voltage gain of 1; diodes connected in series between the signal wire and a positive power supply; diodes connected in series between the signal wire and a negative power supply, wherein an output terminal of the buffer amplifier is connected to a junction point of the diodes and to a junction point of the diodes.
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Citations
14 Claims
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1. A capacitance detection circuit, comprising:
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a first buffer amplifier, wherein an input of said first buffer amplifier is connected to a capacitor to be detected by a signal wire; a first diode and a second diode, connected in series, the anode of the first diode connected to the cathode of the second diode at a first junction point, and the anode of the second diode connected to the signal wire, and the cathode of the first diode connected to a first power supply; a third diode and a fourth diode, connected in series, the anode of the third diode connected to the cathode of the fourth diode at a second junction point, and the cathode of the third diode connected to the signal wire, and the anode of the fourth diode connected to a second power supply; wherein; an output terminal of the first buffer amplifier is connected to the first junction point of the first diode and the second diode via a first capacitance; said output terminal of the first buffer amplifier is connected to the second junction point of the third diode and the fourth diode via a second capacitance; the first junction point is connected to a point having a voltage whose value is between the voltage of the first power supply, and the voltage of the signal wire, via a first resistor; the second junction point is connected to a point having a voltage whose value is between the voltage of the second power supply and the voltage of the signal wire, via a second resistor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A circuit that detects a capacitance of a capacitor, comprising:
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a first buffer amplifier, wherein an input of said first buffer amplifier is connected to the capacitor to be detected by a signal wire, and wherein the voltage gain of the said first buffer amplifier is unity; a first diode and a second diode connected in series between the signal wire and a first power supply, connected so that a current flows from the signal wire to the first power supply via the first and second diodes; a third diode and a fourth diode connected in series between the signal wire and a second power supply, connected so that a current flows from the second power supply to the signal wire via the third and fourth diodes; and a resistor connected between the signal wire and a voltage that is equal to or lower in value than a voltage of the first power supply and equal to or higher than a voltage of the second power supply, wherein; an output terminal of the buffer amplifier is connected to a first junction point of the first diode and the second diode via a first capacitance, and to a second junction point of the third diode and the fourth diode via a second capacitance; the first junction point is connected to a point having a voltage, the value of which is between the voltage of the first power supply and the voltage of the signal wire, via a first resistor; and the second junction point is connected to a point having voltage, the value of which is between the voltage of the second power supply and the voltage of the signal wire, via a second resistor.
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12. A circuit that detects a capacitance of a capacitor, comprising:
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a first buffer amplifier, wherein an input of said first buffer amplifier is connected to the capacitor to be detected by a signal wire, and wherein the voltage gain of the first buffer amplifier is unity; a first diode and a second diode connected in series between the signal wire and a first power supply, connected so that a current flows from the signal wire to the first power supply via the first and second diodes; a third diode and a fourth diode connected in series between the signal wire and a second power supply, connected so that a current flows from the second power supply to the signal wire via the third and fourth diodes; and a resistor connected between the signal wire and a voltage, the value of which is equal to or lower in value than a voltage of the first power supply and equal to or higher than a voltage of the second power supply, a capacitor connected between an output terminal of the first buffer amplifier and a first junction point of the first diode and the second diode; a resistor connected to the first junction point and to a point maintained at a voltage, the value of which is between the voltage of the first power supply and the voltage of the signal wire; a capacitor connected between the output terminal of the first buffer amplifier and a second junction point of the third diode and the fourth diode; and a resistor connected to the second junction point and to a point maintained at a voltage, the value of which is between the voltage of the second power supply and the voltage of the signal wire.
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13. A circuit that detects a capacitance of a capacitor, comprising:
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a first buffer amplifier, wherein an input of said first buffer amplifier is connected to the capacitor to be detected by a signal wire, and wherein the voltage gain of the first buffer amplifier is unity; a first diode and a second diode connected in series between the signal wire and a first power supply, connected so that a current flows from the signal wire to the first power supply via the first and second diodes; a third diode and a fourth diode connected in series between the signal wire and a second power supply, connected so that a current flows from the second power supply to the signal wire via the third and fourth diodes; and a first capacitor and a second buffer amplifier connected in series between an output terminal of the first buffer amplifier and a first junction point of the first diode and the second diode; a first resistor connected to a junction point of the first capacitor and the second buffer amplifier and connected to a point maintained at a voltage, the value of which is between a voltage of the first power supply and a voltage of the signal wire; a second capacitor and a third buffer amplifier connected in series between the output terminal of the first buffer amplifier and a second junction point of the third diode and fourth diode; a second resistor connected to a junction point of the second capacitor and the third buffer amplifier and to a point maintained at a voltage, the value of which is between a voltage of the second power supply and the voltage of the signal wire; and a third resistor connected between the signal wire and a voltage maintained at a value that is equal to or lower than the voltage of the first power supply, and equal to or higher than the voltage of the second power supply.
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14. A method that detects capacitance of a capacitor, comprising:
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connecting the capacitor to be detected and an input of a first buffer amplifier wherein the voltage gain of the first buffer amplifier is unity, via a signal wire; connecting a first diode and a second diode in series between the signal wire and a first power supply and connecting a third diode and a fourth diode in series between the signal wire and a second power supply; and canceling capacitance of the first diode and the third diode connected to the signal wire by connecting an output terminal of the buffer amplifier to a junction point of the first diode and the second diode via a first capacitance and to a junction point of the third diode and the fourth diode via a second capacitance; wherein the first junction point is connected to a point maintained at a voltage, the value of which is between a voltage of the first power supply and a voltage of the signal wire, via a first resistor; and the second junction point is connected to a point maintained at a voltage, the value of which is between a voltage of the second power supply and the voltage of the signal wire, via a second resistor.
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Specification