Touch panel with automatic nulling
First Claim
1. A touch panel device for determining the touch location at which a touch sensing surface of the device is touched comprising:
- signal generator means for producing an alternating-current voltage output;
panel scanning signal applying means for applying panel scanning signals to the touch sensing surface, the panel scanning signal applying means having an input coupled to the signal generator output, the panel scanning signal applying means having first and second panel scanning outputs comprising respective first and second alternating-current voltage panel scanning signals which are driven by the signal generator output and which are one hundred and eighty degrees out of phase from one another;
touch signal detection means having inputs coupled to the first and second panel scanning outputs and a touch signal output, the touch signal detection means comprising means for producing touch current signals at the touch signal output corresponding to the difference between the first and second panel scanning signals;
switching means for selectively coupling the first and second panel scanning outputs to the touch sensing surface so as to selectively apply the first and second panel scanning signals to the touch sensing surface and generate touch current signals at the touch signal output upon touching the touch sensing surface;
panel output signal processing means having a first input coupled to the touch signal output for receiving the touch current signals, the panel output signal processing means comprising means for determining the touch location from the touch signals; and
the panel output signal processing means including nulling circuit means for automatically nulling the touch current signals when the touch sensing surface is untouched.
1 Assignment
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Accused Products
Abstract
A touch panel has panel scanning signals selectively applied to the four sides of a touch sensing surface of the panel so as to establish alternating current voltage gradients in desired directions across the touch sensing surface. When the panel is touched, touch signals result and are utilized by a touch location circuit in determining the location of touch. The impedence touch current resulting from a user'"'"'s touch may also be determined and used. The touch panel circuit automatically compensates for any variations in touch signals which occur when the touch panel is untouched and automatically nulls the touch signals under such circumstances to enhance the accuracy of touch location determination.
191 Citations
20 Claims
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1. A touch panel device for determining the touch location at which a touch sensing surface of the device is touched comprising:
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signal generator means for producing an alternating-current voltage output; panel scanning signal applying means for applying panel scanning signals to the touch sensing surface, the panel scanning signal applying means having an input coupled to the signal generator output, the panel scanning signal applying means having first and second panel scanning outputs comprising respective first and second alternating-current voltage panel scanning signals which are driven by the signal generator output and which are one hundred and eighty degrees out of phase from one another; touch signal detection means having inputs coupled to the first and second panel scanning outputs and a touch signal output, the touch signal detection means comprising means for producing touch current signals at the touch signal output corresponding to the difference between the first and second panel scanning signals; switching means for selectively coupling the first and second panel scanning outputs to the touch sensing surface so as to selectively apply the first and second panel scanning signals to the touch sensing surface and generate touch current signals at the touch signal output upon touching the touch sensing surface; panel output signal processing means having a first input coupled to the touch signal output for receiving the touch current signals, the panel output signal processing means comprising means for determining the touch location from the touch signals; and the panel output signal processing means including nulling circuit means for automatically nulling the touch current signals when the touch sensing surface is untouched. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A touch panel device for determining the touch location at which a touch sensing surface of the device is touched comprising:
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signal generator means for producing an alternating-current voltage output; transformer means having a primary winding means connected to the signal generator output so as to be driven by the signal generator means, the transformer means also having a secondary winding means with first and second secondary winding outputs and a center tap, the secondary winding means providing a panel scanning signal as the primary winding means is driven by the signal generator output; switching means for selectively coupling the secondary winding means to the touch sensing surface so as to selectively apply the panel scanning signal to the touch sensing surface and generate touch current signals at the center tap upon touching of the panel, the switching means comprising means for selectively coupling one of the secondary winding outputs to a first side of the touch sensing surface and the other of the secondary winding outputs to a second side of the touch sensing surface, the second side being located across the touch sensing surface in a first direction from the first side, so as to establish a voltage gradient across the touch sensing surface in the first direction from the first to the second sides and so as to provide a first touch current signal at the center tap when the touch sensing surface is touched, the switching means also comprising means for selectively coupling one of the secondary winding outputs to a third side of the touch sensing surface and the other of the secondary winding outputs to a fourth side of the touch sensing surface, the fourth side being located across the touch sensing surface in a second direction from the first side, so as to establish a voltage gradient across the touch sensing surface in the second direction from the third to the fourth sides and so as to provide a second touch current signal at the center tap when the touch sensing surface. is touched, the switching means comprising means for selectively and simultaneously coupling one of the secondary winding outputs to at least two of the first, second, third and fourth sides of the touch sensing surface to provide an impedance touch current signal at the center tap when the touch sensing surface is touched; panel output signal processing means having a first input coupled to the center tap of the transformer means for receiving the first, second and impedance touch current signals, the panel output signal processing means comprising means for determining the touch location along the first and second directions from the touch current signals; and the panel output signal processing means including nulling circuit means for automatically nulling the first, second and impedance touch current signals when the touch sensing surface is untouched.
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Specification