Capacitance detecting circuit

• US 6,278,283 B1
• Filed: 10/01/1998
• Issued: 08/21/2001
• Est. Priority Date: 05/11/1998
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Tsugai, Masahiro
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): LeRoux, E P
• Application Number:
  US09/164,628
• Time in Patent Office: 1,055 Days
• Field of Search: 324/678, 324/679, 735/143.2, 735/141.8, 327/51
• US Class Current: 324/678
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24

Abstract

A capacitance detecting circuit which can ensure flexibility in application without restriction imposed by a capacitance arrangement such as a single capacitance, differential capacitance, differential capacitance electrostatic servo and like arrangements, to a great advantage includes an operational amplifier having an inverting input terminal and an output terminal between which a feedback capacitance component is connected, a capacitance sensor having an electrostatic capacitance subjected to change under action of an external force, a switch for electrically charging the capacitance component of the capacitance sensor by connecting a charge/discharge terminal of the capacitance component to a reference voltage at a first clock timing for discharging the feedback capacitance component and switching the charge/discharge terminal to the feedback capacitance component at a second clock timing to transfer electric charge, and a sample-and-hold circuit for converting the transferred electric charge to the sensor output voltage.

Claims

1. A capacitance detecting circuit comprising:

a feedback capacitance component;

an operational amplifier having an inverting input terminal and an output terminal, said feedback capacitance component being connected between the inverting input terminal and the output terminal;

a capacitance sensor having an electrostatic capacitance that changes in response to an external force applied to the sensor, said capacitance sensor having a charge/discharge terminal, and a reference terminal connected to a reference voltage; and

charge/discharge control means for disconnecting the charge/discharge terminal from the inverting input terminal of said operational amplifier and connecting the charge/discharge terminal of said capacitance sensor to a reference voltage source during a first time period for charging said electrostatic capacitance, and disconnecting the charge/discharge terminal from the reference voltage source and connecting the charge/discharge terminal to the inverting input terminal of said operational amplifier during a second time period, to transfer electric charge from the charge/discharge terminal of said capacitance sensor to the inverting input terminal of said operational amplifier, said operational amplifier converting the electric charge so transferred to a voltage as an output voltage of said capacitance sensor.

2. The capacitance detecting circuit according to claim 1, wherein said charge/discharge control means short-circuits said feedback capacitance component only during the first time period for discharging said feedback capacitance component.

3. A capacitance detecting circuit comprising:

a feedback capacitance component;

an operational amplifier having an inverting input terminal and an output terminal, said feedback capacitance component being connected between the inverting input terminal and the output terminal;

a differential capacitance sensor having first and second electrostatic capacitances that change in opposite directions in response to an external force applied to the sensor, said first and second electrostatic capacitances having respective charge/discharge terminals, and first and second common terminals, the first and second common terminals being connected to each other; and

charge/discharge control means for disconnecting the first and second charge/discharge terminals of said first and second electrostatic capacitances from the inverting input terminal of said operational amplifier and connecting the first and second charge/discharge terminals of said first and second electrostatic capacitances to first and second reference voltage sources during a first time period for charging said first and second electrostatic capacitances, and disconnecting the first and second charge/discharge terminals from the first and second reference voltage sources and connecting the first and second charge/discharge terminals to the inverting input terminal of said operational amplifier during a second time period, to transfer electric charge from the first and second charge/discharge terminals to the inverting input terminal of said operational amplifier, said operational amplifier converting the electric charge so transferred to a voltage as an output voltage of said differential capacitance sensor.

4. The capacitance detecting circuit according to claim 3, comprising feedback control means for feeding back the output voltage to the common terminals of said first and second electrostatic capacitances.

5. The capacitance detecting circuit according to claim 3, wherein said charge/discharge control means short-circuits said feedback capacitance component only during the first time period for discharging said feedback capacitance component.

6. A capacitance detecting circuit comprising:

first and second feedback capacitance components;

a first operational amplifier having an inverting input terminal and an output terminal, said first feedback capacitance component being connected between the inverting input terminal and the output terminal of said first operational amplifier;

a second operational amplifier having an inverting input terminal and an output terminal, said second feedback capacitance component being connected between the inverting input terminal and the output terminal of said second operational amplifier;

a differential capacitance sensor having first and second electrostatic capacitances that change in opposite directions in response to an external force applied to the sensor, said first and second electrostatic capacitances having respective charge/discharge terminals, and first and second common terminals, the first and second common terminals being connected to each other; and

charge/discharge control means for disconnecting said first and second electrostatic capacitances from the inverting input terminals of said first and second operational amplifiers and connecting the first and second charge/discharge terminals of said first and second electrostatic capacitances to the second reference voltage source during a first time period for charging said first and second electrostatic capacitances, and disconnecting the first and second charge/discharge terminals from the first reference voltage source and connecting the first and second charge/discharge terminals respectively to the inverting input terminals of said first and second operational amplifier during a second time period, to transfer electric charge to the inverting input terminal of said first and second operational amplifiers, said first and second operational amplifiers converting the electric charge so transferred to first and second voltages as output voltages of said differential capacitance sensor.

7. The capacitance detecting circuit according to claim 6, comprising difference voltage output means receiving the first and second voltages and determining a difference voltage between the first and second voltages, and outputting the difference voltage as a voltage conversion value.

8. The capacitance detecting circuit according to claim 7, comprising feedback control means for feeding back the voltage conversion value as a reference voltage to the first and second common terminals of said first and second electrostatic capacitances of said differential capacitance sensor.

9. The capacitance detecting circuit according to claim 6, wherein said charge/discharge control means short-circuits said first and second feedback capacitance components only during the first time period for discharging said first and second feedback capacitance components.