Capacitance Detection Circuit and and Capacitance Detection Method

• US 20080150553A1
• Filed: 08/05/2004
• Published: 06/26/2008
• Est. Priority Date: 08/06/2003
• Status: Active Grant

• Current Assignee: Tokyo Electron Limited
• Original Assignee: Tokyo Electron Limited
• Inventors: Yakabe, Masami
• Granted Patent: US 7,557,590 B2
• Time in Patent Office: Days
• US Class Current: 324/686
• CPC Class Codes: H04R 3/00 Circuits for transducers , loudspeakers or microphones

Abstract

A capacitance detection circuit containing an input protection circuit and having high sensitivity is provided. A capacitance detection circuit (20) for detecting the capacitance of a capacitive sensor (Cs), comprising a buffer amplifier (12) connected to the capacitive sensor (Cs) via a signal wire (13) and having a voltage gain of 1; diodes (Dp1, Dp2) connected in series between the signal wire (13) and a positive power supply (+Vdd); diodes (Dm1, Dm2) connected in series between the signal wire (13) and a negative power supply (−Vdd), wherein an output terminal of the buffer amplifier (12) is connected to a junction point (21a) of the diodes (Dp1 and Dp2) and to a junction point (21b) of the diodes (Dm1 and Dm2).

Claims

1. A capacitance detection circuit comprising:

a first buffer amplifier unit connected to a capacitor to be detected via a signal wire;

a first diode and a second diode connected in series between the signal wire and a first power supply; and

a third diode and a fourth diode connected in series between the signal wire and a second power supply,

wherein an output terminal of the first buffer amplifier unit is connected to a first junction point of the first diode and the second diode and to a second junction point of the third diode and the fourth diode.

2. The capacitance detection circuit according to claim 1,

wherein a voltage gain of the first buffer amplifier unit is 1.

3. The capacitance detection circuit according to claim 1,

wherein the output terminal of the first buffer amplifier unit is connected to the first junction point via a first capacitance and to the second junction point via a second capacitance,

the first junction point is connected to a point having potential between potential of the first power supply and potential of the signal wire via a first resistor, and

the second junction point is connected to a point having potential between potential of the second power supply and potential of the signal wire via a second resistor.

4. The capacitance detection circuit according to claim 3,

wherein the first resistor and the first capacitor are, respectively, a resistance value and a capacitance value that pass frequency elements of output signals from the first buffer amplifier unit corresponding to variant capacitance of the capacitor to be detected and AC component of biased voltage added to said capacitor to be detected, and

the second resistor and the second capacitor are, respectively, a resistance value and a capacitance value that pass frequency elements of output signals from the first buffer amplifier unit corresponding to variant capacitance of the capacitor to be detected and AC component of biased voltage added to said capacitor to be detected.

5. The capacitance detection circuit according to claim 3, further comprising:

a second buffer amplifier unit connected between (i) a junction point of the first resistor and the first capacitor and (ii) the first junction point; and

a third buffer amplifier unit connected between (i) a junction point of the second resistor and the second capacitor and (ii) the second junction point.

6. The capacitance detection circuit according to claim 5,

wherein each voltage gain of the first to third buffer amplifier units is set so that potential of the first junction point and potential of the second junction point are same as potential of the signal wire.

7. The capacitance detection circuit according to claim 1,

wherein the first buffer amplifier unit includes a MOSFET as an input circuit,

a gate of the MOSFET is connected to an input terminal of the first buffer amplifier unit, and

a substrate of the MOSFET is connected to an output terminal of the first buffer amplifier unit.

8. The capacitance detection circuit according to claim 1, further comprising:

a testing terminal for an input of a testing signal; and

a testing capacitor and a switch connected in series between the input terminal of the first buffer amplifier unit and the testing terminal.

9. A circuit that detects capacitance of a capacitor to be detected, comprising:

a buffer amplifier unit connected to the capacitor to be detected via a signal wire and of which voltage gain is 1;

a first diode and a second diode connected in series between the signal wire and a first power supply in a way 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 in a way 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 potential that is equal to or lower than potential of the first power supply and equal to or higher than potential of the second power supply,

wherein an output terminal of the buffer amplifier unit is connected to a junction point of the first diode and the second diode and to a junction point of the third diode and the fourth diode.

10. A circuit that detects capacitance of a capacitor to be detected comprising:

a buffer amplifier unit connected to the capacitor to be detected via a signal wire and of which voltage gain is 1;

a first diode and a second diode connected in series between the signal wire and a first power supply in a way 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 in a way that a current flows from the second power supply to the signal wire via the third and fourth diodes;

a resistor connected between (i) potential that is equal to or lower than potential of the first power supply and equal to or higher than potential of the second power supply and (ii) the signal wire,

a capacitor connected between an output terminal of the buffer amplifier unit 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 having potential between potential of the first power supply and potential of the signal wire;

a capacitor connected between the output terminal of the buffer amplifier unit 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 having potential between potential of the second power supply and potential of the signal wire.

11. A circuit that detects capacitance of a capacitor to be detected, comprising:

a first buffer amplifier unit connected to the capacitor to be detected via a signal wire and of which voltage gain is 1;

a first diode and a second diode connected in series between the signal wire and a first power supply in a way 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 in a way that a current flows from the second power supply to the signal wire via the third and fourth diodes;

a first capacitor and a second buffer amplifier unit connected in series between an output terminal of the first buffer amplifier unit 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 unit and to a point having potential between potential of the first power supply and potential of the signal wire;

a second capacitor and a third buffer amplifier unit connected in series between the output terminal of the first buffer amplifier unit 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 unit and to a point having potential between potential of the second power supply and potential of the signal wire; and

a third resistor connected between (i) potential that is equal to or lower than potential of the first power supply and equal to or higher than potential of the second power supply and (ii) the signal wire.

12. A method that detects capacitance of a capacitor to be detected, comprising:

connecting the capacitor to be detected and a buffer amplifier unit of which voltage gain is 1 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 unit to a junction point of the first diode and the second diode and to a junction point of the third diode and the fourth diode.