Capacitance detecting apparatus
First Claim
1. A capacitance detecting apparatus comprising:
- a first differential amplifier including an inverting input terminal, a non-inverting input terminal, and an output terminal, the non-inverting input terminal inputting a first fixed voltage;
a first reference capacitor including a first electrode connected to the output terminal of the first differential amplifier and a second electrode connected to the inverting input terminal of the first differential amplifier;
a first on/off switch including a first end connected to the output terminal of the first differential amplifier and a second end connected to the inverting input terminal of the first differential amplifier;
a second on/off switch including a first end connected to the inverting input terminal of the first differential amplifier;
a third on/off switch including a first end connected to a first power-supply voltage and a second end connected to the second end of the second on/off switch;
a first sensor electrode connected to the second end of the second on/off switch and facing a ground electrode having a constant electric potential, a first variable capacitance being formed between the first sensor electrode and the ground electrode in response to a distance between the first sensor electrode and the ground electrode;
switch controlling means for performing a first switch operation in which the first on/off switch is shifted to a closed state and returned to an open state, and then alternately repeating a second switch operation in which the second on/off switch is shifted to a closed state and returned to an open state and a third switch operation in which the third on/off switch is shifted to a closed state and returned to an open state;
a comparator including a first input terminal connected to the output terminal of the first differential amplifier and a second input terminal inputting a voltage, the comparator comparing an output voltage from the first differential amplifier and the voltage input to the second input terminal;
counting means for counting the number of times the second switch operation is repeated; and
determining means for determining changes in the first variable capacitance formed between the first sensor electrode and the ground electrode based on the number of times the second switch operation is repeated that is counted by the counting means before an output level of the comparator is changed.
1 Assignment
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Accused Products
Abstract
A capacitance detecting apparatus includes a first differential amplifier, a first reference capacitor, a first on/off switch, a second on/off switch, a third on/off switch, a first sensor electrode facing a ground electrode, a first variable capacitance being formed between the first sensor electrode and the ground electrode in response to a distance between the first sensor electrode and the ground electrode, switch controlling means for performing first to third switch operations, a comparator comparing an output voltage from the first differential amplifier and a voltage input to one of input terminals, counting means for counting the number of times the second switch operation is repeated, and determining means for determining changes in the first variable capacitance based on the number of times the second switch operation is repeated before an output level of the comparator is changed.
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Citations
14 Claims
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1. A capacitance detecting apparatus comprising:
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a first differential amplifier including an inverting input terminal, a non-inverting input terminal, and an output terminal, the non-inverting input terminal inputting a first fixed voltage; a first reference capacitor including a first electrode connected to the output terminal of the first differential amplifier and a second electrode connected to the inverting input terminal of the first differential amplifier; a first on/off switch including a first end connected to the output terminal of the first differential amplifier and a second end connected to the inverting input terminal of the first differential amplifier; a second on/off switch including a first end connected to the inverting input terminal of the first differential amplifier; a third on/off switch including a first end connected to a first power-supply voltage and a second end connected to the second end of the second on/off switch; a first sensor electrode connected to the second end of the second on/off switch and facing a ground electrode having a constant electric potential, a first variable capacitance being formed between the first sensor electrode and the ground electrode in response to a distance between the first sensor electrode and the ground electrode; switch controlling means for performing a first switch operation in which the first on/off switch is shifted to a closed state and returned to an open state, and then alternately repeating a second switch operation in which the second on/off switch is shifted to a closed state and returned to an open state and a third switch operation in which the third on/off switch is shifted to a closed state and returned to an open state; a comparator including a first input terminal connected to the output terminal of the first differential amplifier and a second input terminal inputting a voltage, the comparator comparing an output voltage from the first differential amplifier and the voltage input to the second input terminal; counting means for counting the number of times the second switch operation is repeated; and determining means for determining changes in the first variable capacitance formed between the first sensor electrode and the ground electrode based on the number of times the second switch operation is repeated that is counted by the counting means before an output level of the comparator is changed. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A capacitance detecting apparatus comprising:
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a first differential amplifier including an inverting input terminal, a non-inverting input terminal, and an output terminal, the non-inverting input terminal inputting a first fixed voltage; a first reference capacitor including a first electrode connected to the output terminal of the first differential amplifier and a second electrode connected to the inverting input terminal of the first differential amplifier; a first on/off switch including a first end connected to the output terminal of the first differential amplifier and a second end connected to the inverting input terminal of the first differential amplifier; a second on/off switch including a first end connected to the inverting input terminal of the first differential amplifier; a third on/off switch including a first end connected to a first power-supply voltage and a second end connected to the second end of the second on/off switch; a first sensor electrode connected to the second end of the second on/off switch and facing a ground electrode having a constant electric potential, a first variable capacitance being formed between the first sensor electrode and the ground electrode in response to a distance between the first sensor electrode and the ground electrode; a second differential amplifier including an inverting input terminal, a non-inverting input terminal, and an output terminal, the non-inverting input terminal inputting a second fixed voltage; a second referential capacitor including a first electrode connected to the output terminal of the second differential amplifier and a second electrode connected to the inverting input terminal of the second differential amplifier; a fourth on/off switch including a first end connected to the output terminal of the second differential amplifier and a second end connected to the inverting input terminal of the second differential amplifier; a fifth on/off switch including a first end connected to the inverting input terminal of the second differential amplifier; a sixth on/off switch including a first end connected to a second power-supply voltage and a second end connected to the second end of the fifth on/off switch; a second sensor electrode connected to the second end of the fifth on/off switch and facing a ground electrode, a second variable capacitance being formed between the second sensor electrode and the ground electrode in response to a distance between the second sensor electrode and the ground electrode; switch controlling means for performing a first switch operation in which the first on/off switch and the fourth on/off switch are each shifted to a closed state and returned to an open state, and then alternately repeating a second switch operation in which the second on/off switch and the fifth on/off switch are each shifted to a closed state and returned to an open state and a third switch operation in which the third on/off switch and the sixth on/off switch are each shifted to a closed state and returned to an open state; a comparator including a first input terminal connected to the output terminal of the first differential amplifier and a second input terminal connected to the output terminal of the second differential amplifier, the comparator comparing an output voltage from the first differential amplifier and an output voltage from the second differential amplifier; counting means for counting the number of times the second switch operation is repeated; and determining means for determining changes in one of the first and second variable capacitances formed between the first and second sensor electrodes and the ground electrode, respectively, based on the number of times the second switch operation is repeated that is counted by the counting means before an output level of the comparator is changed. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification