Proximity/touch detector and calibration circuit
First Claim
1. A calibration circuit, comprising:
- a transistor and a first capacitor coupled to each other;
a second capacitor coupled in series with the first capacitor and the transistor;
a capacitive sensor coupled in series with the second capacitor, the first capacitor and the transistor;
an oscillator coupled to the capacitive sensor and the second capacitor; and
a microprocessor coupled to turn the transistor “
on”
to decrease an actual input capacitance to the oscillator to simulate an input capacitance associated with an object not being in contact with the capacitive sensor or to turn the transistor “
off”
to increase an actual input capacitance to the oscillator to simulate an input capacitance associated with an object being in contact with the capacitive sensor.
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Accused Products
Abstract
A calibration circuit and method for a proximity/touch detector allow automatic calibration to the proximity/touch detector components, chassis affects, and ambient conditions such that initial factory calibration and periodic manual calibration are not needed. The calibration circuit switches a capacitance into the input capacitance of a Schmitt trigger free running oscillator to change the output frequency of the oscillator. A capacitive sensor forms part of the input capacitance. The change in frequency simulates the frequency shift associated with the difference in input capacitance generated when an object, such as a finger, is touching the capacitive sensor and when the capacitive sensor is free from contact with the object.
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Citations
9 Claims
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1. A calibration circuit, comprising:
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a transistor and a first capacitor coupled to each other;
a second capacitor coupled in series with the first capacitor and the transistor;
a capacitive sensor coupled in series with the second capacitor, the first capacitor and the transistor;
an oscillator coupled to the capacitive sensor and the second capacitor; and
a microprocessor coupled to turn the transistor “
on”
to decrease an actual input capacitance to the oscillator to simulate an input capacitance associated with an object not being in contact with the capacitive sensor or to turn the transistor “
off”
to increase an actual input capacitance to the oscillator to simulate an input capacitance associated with an object being in contact with the capacitive sensor.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
a Schmitt trigger; and
a feedback resistor coupled from an output of the Schmitt trigger to an input of the Schmitt trigger.
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7. The apparatus of claim 1, further comprising a resistor coupled between the collector of the transistor and a supply voltage.
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8. The calibration circuit of claim 1, further comprising a resistor coupled between the collector of the transistor and a supply voltage to reduce the capacitance at the collector when the transistor is turned “
- off.”
- off.”
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9. The calibration circuit of claim 1, further comprising a resistor coupled between the collector of the transistor and a supply voltage to modify the impedance seen by the oscillator when the transistor is turned “
- off.”
- off.”
Specification
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- Resources
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Current AssigneeApple Inc.
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Original AssigneeApple Computer Incorporated (Apple Inc.)
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InventorsKrah, Christoph H., Cappels, Richard D.
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Primary Examiner(s)Lam, Tuan T.
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Assistant Examiner(s)Nguyen, Hiep
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Application NumberUS09/886,237Publication NumberTime in Patent Office734 DaysField of Search331/65, 331/74, 178/18.06, 178/19.03, 345/174, 345/862US Class Current331/74CPC Class CodesH03K 17/962 Capacitive touch switchesH03K 2217/94026 Automatic threshold calibra...
