NOISE COMPENSATION TECHNIQUES FOR CAPACITIVE TOUCH SCREEN SYSTEMS
First Claim
1. A method for detecting touch operations performed a capacitive touch screen system, comprising:
- determining an optimum integration time for control sampling touch screen conductors, wherein the optimum integration time compensates for noise on the touch screen conductors;
injecting excitation signals to conductors of the capacitive touch screen;
sampling return signals from the conductors; and
resolving touch locations based on profiles for the return signals.
1 Assignment
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Accused Products
Abstract
Noise compensation techniques for capacitive touch screen systems. The techniques may include measurement operations that may measure coupled noise frequencies that may be induced on a capacitive touch screen. Noise measurement techniques may include driving a stimulus voltage(s) to a conductor(s) of a capacitive touch screen and sampling return signals from a touch screen conductor(s). Noise measurement techniques may further include sampling ambient return signals from a touch screen conductor(s) in the absence of a stimulus voltage(s). Coupled noise frequencies may also be calculated from a first measured noise frequency. A touch screen control system may use measured or calculated coupled noise frequencies to configure operational parameters that may compensate for the coupled noise during operation of the capacitive touch screen.
64 Citations
42 Claims
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1. A method for detecting touch operations performed a capacitive touch screen system, comprising:
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determining an optimum integration time for control sampling touch screen conductors, wherein the optimum integration time compensates for noise on the touch screen conductors; injecting excitation signals to conductors of the capacitive touch screen; sampling return signals from the conductors; and resolving touch locations based on profiles for the return signals. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for determining an optimum integration time for control of touch screen conductor measurement circuits, comprising:
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measuring noise from a capacitive touch screen for a plurality of integration times within a range of integration times; determining one or more local minimums for the measure noise at the plurality of integration times; and setting the optimum integration time to an integration time corresponding to the lowest local minimum. - View Dependent Claims (9, 10)
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11. A method for calibrating parasitic capacitances for touch screen conductor crosspoints, comprising:
on an iterative basis for each conductor of the touch screen; measuring capacitance for a conductor; comparing the measured capacitance against a predetermined capacitance threshold; if the measured capacitance is above the threshold, approximating the parasitic capacitance for each crosspoint of the conductor; if the measured capacitance is below the predetermined capacitance threshold, measuring noise for the conductor, comparing the noise to a predetermined noise threshold, if the measured noise is above the predetermined noise threshold, approximating the parasitic capacitance for each crosspoint of the conductor, and if the measured noise is below the predetermined noise threshold, calibrating the parasitic capacitance for each crosspoint of the conductor. - View Dependent Claims (12)
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13. A measurement system, comprising:
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driver circuits to drive stimulus signals to a pair of circuit terminals for connection to touch screen conductors; sampling units to capture return signals from the terminals; and a processor to estimate noise on the touch screen conductors based on the return signals. - View Dependent Claims (14, 15, 16, 17)
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18. A measurement system, comprising:
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a driver circuit to drive stimulus voltages to a first terminal connected to a first touch screen conductor; and a sampling unit to capture return charges from a second terminal connected to a second touch screen conductor, the return charges being captured while the stimulus voltages are driven to the first touch screen conductor; and a processor to estimate noise of the first conductor and second conductor based on the return charges. - View Dependent Claims (19, 20, 21)
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22. A measurement circuit for measuring noise from capacitive touch screen conductors coupled to I/O terminals of the measurement circuit, comprising:
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a differential operational amplifier (op-amp) having a pair of inputs and a pair of outputs; integrating capacitors each coupling a respective op-amp output to an op-amp input; and a switching network having a plurality of switches connecting a first I/O terminal to each of a pair of stimulus voltages, and connecting a second I/O terminal to each op-amp input. - View Dependent Claims (23, 24, 25, 26)
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27. A method for measuring noise from conductors of a capacitive touch screen, comprising:
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in a first measurement cycle; driving respective stimulus signals to first and second touch screen conductors; capturing return signals from the first and second touch screen conductors; in a second measurement cycle; driving respective stimulus signals to the first and second touch screen conductors; capturing return signals from the first and second touch screen conductors; comparing the return signals of the two measurement cycles; and estimating noise on the touch screen conductors based on the comparison. - View Dependent Claims (28, 29, 30)
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31. A method for measuring noise from conductors of a capacitive touch screen, comprising:
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in a first measurement cycle; driving a first stimulus signal to a first touch screen conductor; capturing a return signal from a second touch screen conductor; in a second measurement cycle; driving a second stimulus signal to the first touch screen conductor; capturing a return signal from the second touch screen conductor; comparing the return signals of the two measurement cycles; and estimating noise on the first and second touch screen conductors based on the comparison. - View Dependent Claims (32, 33)
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34. A touch screen control system for a capacitive touch screen, comprising:
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a measurement system to drive stimulus signals to capacitive touch screen conductors and capture return signals from the conductors; a detection system, comprising a plurality of signal generators, each to generate and drive an excitation signal having a unique spectral profile to conductors of the capacitive touch screen, and at least one analog-to-digital converter to sample return signals from conductors of the capacitive touch screen; and a processor to estimate noise on the conductors based on the measurement system return signals, and to determine touch locations based on the detection system return signals. - View Dependent Claims (35, 36, 37, 38)
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39. A method for measuring noise from conductors of a capacitive touch screen, comprising:
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coupling a first touch screen conductor to a common mode voltage; capturing a first return signal from a second touch screen conductor and a second return signal from the second touch screen conductor; comparing the first and second return signals; and estimating noise on the first and second touch screen conductors based on the comparison.
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40. A method for measuring noise from conductors of a capacitive touch screen, comprising:
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in a first measurement cycle; coupling a first touch screen conductor to a common mode voltage, and capturing a return signal from a second touch screen conductor at an inverting input of an op-amp; in a second measurement cycle; coupling the first touch screen conductor to the common mode voltage, and capturing a return signal from the second touch screen conductor at a non-inverting input of an op-amp; comparing the return signals of the two measurement cycles; and estimating noise on the first and second touch screen conductors based on the comparison.
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41. A method for measuring noise from conductors of a capacitive touch screen, comprising:
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in a first cycle; coupling a touch screen conductor to a common mode voltage; in a second cycle; capturing a return signal from the touch screen conductor, and providing the return signal to a non-inverting input of an op-amp; in a third cycle; coupling the touch screen conductor to the common mode voltage; in a fourth cycle; capturing a return signal from the touch screen conductor, and providing the return signal to an inverting input of the op-amp; and estimating noise on the touch screen conductor based on the return signals from the second and fourth cycles.
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42. A touch screen control system for a capacitive touch screen, comprising:
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a measurement system to provide a common mode voltage to at least one of the capacitive touch screen conductors and capture return signals from at least one of the conductors; a detection system, comprising at least one analog-to-digital converter to sample signals from conductors of the capacitive touch screen; and a processor to estimate noise on the conductors based on the measurement system signals, and to determine touch locations based on the detection system return signals.
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Specification