Capacitive sensor system with noise reduction
First Claim
1. A system for reducing noise when detecting a capacitance value of a capacitor in a touch display that operates in a potentially noisy environment, comprising:
- a capacitance sensor for determining a size of the capacitor in the touch screen display and the capacitor sensor including a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero;
a control circuit that controls the capacitance sensor charging and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation;
wherein the control circuit operating in accordance with the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value; and
noise reduction circuitry for modifying the operation of the control circuit to reduce noise without repeating the charge and discharge of the capacitor.
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Accused Products
Abstract
A system for reducing noise when detecting the capacitance value of a capacitor in a touch display that operates in a potentially noisy environment. A capacitance sensor is provided for determining the size of the capacitor in the touch screen display and includes a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero. A control circuit controls the capacitance sensor and the operation of the charge and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation. The operation of the control circuit and the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value. A noise reduction circuit is provided to modify the operation of the control circuit to reduce noise.
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Citations
11 Claims
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1. A system for reducing noise when detecting a capacitance value of a capacitor in a touch display that operates in a potentially noisy environment, comprising:
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a capacitance sensor for determining a size of the capacitor in the touch screen display and the capacitor sensor including a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero; a control circuit that controls the capacitance sensor charging and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation; wherein the control circuit operating in accordance with the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value; and noise reduction circuitry for modifying the operation of the control circuit to reduce noise without repeating the charge and discharge of the capacitor. - View Dependent Claims (2)
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3. A system disposed on an integrated circuit for reducing noise when detecting a capacitance value of a capacitor external to the integrated circuit in a touch display that operates in a potentially noisy environment, comprising:
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a capacitance sensor for determining a size of the capacitor in the touch screen display and the capacitor sensor including a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero; a control circuit that controls the capacitance sensor charging and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation; wherein the control circuit operating in accordance with the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value; noise reduction circuitry for modifying the operation of the control circuit to reduce noise, wherein the noise is internally generated in the integrated circuit; and the noise reduction circuitry includes a detector for detecting and determining when the noise has been generated and the noise reduction circuitry modifying the operation of the control circuit during portions of the charging/discharging operation when the noise is above a certain level during such portions.
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4. A system disposed on an integrated circuit for reducing noise when detecting a capacitance value of a capacitor external to the integrated circuit in a touch display that operates in a potentially noisy environment, comprising:
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a capacitance sensor for determining a size of the capacitor in the touch screen display and the capacitor sensor including a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero; a control circuit that controls the capacitance sensor charging and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation; wherein the control circuit operating in accordance with the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value; and noise reduction circuitry for modifying the operation of the control circuit to reduce noise; wherein the charging and discharge circuits operate to deliver a bit value in a SAR operation in accordance with the SAR algorithm of the ADC having a fixed bit length and resolution, the control circuit operable to control the charging circuit and the discharge circuit to successively charge and discharge the capacitor in accordance with a SAR operation and the noise reduction circuitry is operable to vary the resolution of the SAR operation as a function of noise. - View Dependent Claims (5, 6)
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7. A system disposed on an integrated circuit for reducing noise when detecting a capacitance value of a capacitor external to the integrated circuit in a touch display that operates in a potentially noisy environment, comprising:
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a capacitance sensor for determining a size of the capacitor in the touch screen display and the capacitor sensor including a charging circuit that charges the capacitor and a discharge circuit that resets the charge of the capacitor to substantially zero; a control circuit that controls the capacitance sensor charging and discharge circuits in accordance with a predetermined charging/discharging algorithm to resolve the value of the capacitor and output such value in a sampling operation; wherein the control circuit operating in accordance with the charging/discharging algorithm is subject to errors as a function of the noisy environment, which errors will be reflected in the output value; and noise reduction circuitry for modifying the operation of the control circuit to reduce noise, wherein the discharge circuit includes; a first discharge circuit for discharging the capacitor through a low impedance path to ground; a second discharge circuit for discharging the capacitor through a high impedance path to ground; and the noise reduction circuitry including timing circuitry to control the first and second discharge circuitry to first discharge the capacitor during a discharge operation through the low impedance path to remove a substantial portion of charge therefrom followed by discharging the capacitor through the high impedance path such that the second discharge circuit operates as a low pass filter to remove high frequency external noise from the capacitor. - View Dependent Claims (8, 9, 10, 11)
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Specification