Low power capacitive touch detector
First Claim
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1. A method of detecting a capacitive touch input, the method comprising:
- charging a parasitic capacitor of a capacitive sensor;
enabling the parasitic capacitor to discharge through a resistor coupled to the parasitic capacitor, wherein the discharge is in a first current direction through the resistor;
timing the discharge of the parasitic capacitor through the resistor to produce a first discharge time;
thencharging the parasitic capacitor again;
enabling the parasitic capacitor to discharge through the resistor in a second current direction opposite to the first current direction;
timing the discharge of the parasitic capacitor through the resistor to produce a second discharge time; and
detecting a touch event based on the first discharge time and the second discharge time.
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Abstract
A low power capacitive detector is disclosed. The detector includes a mechanism to measure and detect touch on capacitive sensors. The detector uses signal processing to suppress noise and increase sensitivity. The detector does not require dedicated analog circuitry, making it easy to adopt in a microcontroller system. The detector can be scaled to a larger number of capacitive sensors without noticeable increase in silicon cost.
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Citations
20 Claims
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1. A method of detecting a capacitive touch input, the method comprising:
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charging a parasitic capacitor of a capacitive sensor; enabling the parasitic capacitor to discharge through a resistor coupled to the parasitic capacitor, wherein the discharge is in a first current direction through the resistor; timing the discharge of the parasitic capacitor through the resistor to produce a first discharge time;
thencharging the parasitic capacitor again; enabling the parasitic capacitor to discharge through the resistor in a second current direction opposite to the first current direction; timing the discharge of the parasitic capacitor through the resistor to produce a second discharge time; and detecting a touch event based on the first discharge time and the second discharge time. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A capacitive touch detection system, comprising:
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a capacitance counter configured to generate a count value proportional to a parasitic capacitance of a parasitic capacitor of a first capacitive sensor coupled to the capacitance counter, the count value being generated based on a number of first occurrences and a number of second occurrences, the number of first occurrences being counted when an input signal detected by the capacitance counter has a first value during a first time period and the number of second occurrences being counted when the input signal has a second, different value during a second time period successive to the first time period; a signal processing subsystem configured for processing the count value; and one or more detectors configured for detecting a touch event based on the processed count value exceeding one or more threshold values. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification