Method and apparatus for improving dynamic range of a touchscreen controller
First Claim
1. A capacitance-to-voltage converter configured to be utilized by a capacitive touchscreen having one or more capacitance sensors, the converter comprising:
- a capacitance offset cancellation element coupled for alleviating effects of parasitic capacitance on signals produced by one or more of the capacitance sensors;
a analog-to-digital converter coupled to the offset cancellation element for converting the signals to digital signals; and
a controller coupled to the offset cancellation element for dynamically adjusting the extent to which the offset cancellation element alleviates the effects of the parasitic capacitance based on the digital signals, wherein the controller averages the value of the digital signals to determine a baseline value, the controller configured to adjust an offset value of the offset cancellation element by a delta value such that the baseline is moved away from a threshold value when the baseline reaches the threshold value.
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Abstract
A touchscreen system for increasing the dynamic range of the system comprising a touchscreen coupled to an offset cancellation element and a capacitance measuring element. The offset cancellation element is configured to be dynamically changed in capacitance such that it offsets parasitic and sensor capacitances of the touchscreen sensors thereby leaving only touch event capacitance to be measured by the measuring element. The offset cancellation element is able to adjust to the initial unwanted capacitances of each sensor as well as dynamically adjust to changes in the unwanted capacitance due to the environment. In some embodiments, the offset cancellation element is a capacitance digital-to-analog converter that is controlled by a controller for offsetting the unwanted capacitance. As a result, the touchscreen system is able to utilize a small integrating capacitor thereby lowering cost and improving the dynamic range of the system.
55 Citations
30 Claims
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1. A capacitance-to-voltage converter configured to be utilized by a capacitive touchscreen having one or more capacitance sensors, the converter comprising:
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a capacitance offset cancellation element coupled for alleviating effects of parasitic capacitance on signals produced by one or more of the capacitance sensors; a analog-to-digital converter coupled to the offset cancellation element for converting the signals to digital signals; and a controller coupled to the offset cancellation element for dynamically adjusting the extent to which the offset cancellation element alleviates the effects of the parasitic capacitance based on the digital signals, wherein the controller averages the value of the digital signals to determine a baseline value, the controller configured to adjust an offset value of the offset cancellation element by a delta value such that the baseline is moved away from a threshold value when the baseline reaches the threshold value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A touchscreen system comprising:
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a capacitive touch screen having one or more capacitance sensors; and a capacitance-to-voltage converter comprising; a capacitance offset cancellation element coupled for alleviating effects of parasitic capacitance on signals produced by one or more of the capacitance sensors; a analog-to-digital converter coupled to the offset cancellation element for converting the signals to digital signals; and a controller coupled to the offset cancellation element for dynamically adjusting the extent to which the offset cancellation element alleviates the effects of the parasitic capacitance based on the digital signals, wherein an offset value of the offset cancellation element is initially set to at least one of zero or a maximum value such that all of the effects of the parasitic capacitance are alleviated when the offset value is initially set to the maximum value, wherein the controller incrementally increases the offset value from the initial zero value until the digital signals reach a predetermined value when the offset value is initially set to zero or the controller incrementally decreases the offset value from the initial maximum value until the digital signals reach a predetermined value when the offset value is initially set to the maximum value. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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21. A method of improving dynamic range of a capacitance-to-voltage converter utilized by a touchscreen having one or more capacitance sensors, the method comprising:
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determining an average digital output over a period with a controller, wherein the average digital output is associated with a sensor of the converter; at least one of initially setting an offset value of a capacitance offset cancellation element to zero or to a maximum value; adjusting the offset value produced by the capacitance offset cancellation element of the converter until the digital output of the converter is equal to a predetermined baseline value, wherein the capacitance offset cancellation element is a capacitive digital-to-analog converter; and at least one of incrementally increasing the offset value from the initial zero value until the digital output equals the predetermined baseline value when the offset value is initially set to zero or incrementally decreasing the offset value from the initial maximum value until the digital output equals the predetermined baseline value when the offset value is initially set to the maximum value. - View Dependent Claims (22, 23)
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24. A method of improving dynamic range in a capacitance-to-voltage converter utilized by a touchscreen having one or more capacitance sensors, the method comprising:
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averaging a digital output associated with a sensor of the converter in order to determine a baseline value; determining a baseline threshold value; and dynamically adjusting an offset value of an offset cancellation element of the converter by a delta value if when the baseline value reaches the baseline threshold value such that the baseline value is distanced from the threshold value, wherein the averaging the digital output comprises disregarding the values of the digital output when a touch event causes the values of the digital output to increase and drop in a time period that is less than a predetermined touch period. - View Dependent Claims (25, 26, 27, 28, 29, 30)
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Specification