Capacitive touch panel system with randomly modulated position measurement signal
First Claim
1. In a display system including a display surface positioned adjacent an optically transparent, electrically conductive layer having a first resistivity and first and second opposed side margins of preselected lengths, a position address encoder for generating an address signal indicative of a location on the conductive layer in contact with a stylus that is electrically connected to a reference potential, comprising:
- signal generating means for generating a time-varying position measurement signal of a preselected magnitude and a frequency that varies in a substantially random manner;
first and second electrodes positioned along the lengths of the respective first and second opposed side margins and receiving the position measurement signal generated by the signal generating means, the resistivity of the conductive layer establishing an effective total resistance between the first and second electrodes; and
current measuring means for measuring currents corresponding to the position measurement signal and drawn through the first and second electrodes whenever a stylus contacts the conductive layer, whereby the stylus contacting the conductive layer divides the total resistance into first and second resistances that cause currents to be drawn through the respective first and second electrodes in proportion to the separation between the electrodes and the location.
1 Assignment
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Accused Products
Abstract
A capacitive touch panel system (10) having a faceplate (14) with an electrically conductive layer (20) of a consistent resistivity employs a position measurement apparatus (12) to generate an address signal indicative of a position (46) on the faceplate in contact with a stylus (48). The position measurement apparatus includes a position measurement signal source (56) that generates a square-wave measurement signal of a frequency that varies in a substantially random manner. The position measurement signal is applied to a first pair of opposed electrodes (36) and (40) and a second pair of opposed electrodes (38) and (42) positioned along respective side margins (26, 30, 28, and 32) of the faceplate. The resistivity of the conductive layer establishes effective resistances of Rx and Ry between the respective first and second pairs of electrodes. Position measurement subcircuits (54a-54d) are locked-in with the random measurement signal frequencies to measure currents drawn through the electrodes whenever the stylus contacts the conductive layer, thereby to form an address signal indicative of the location at which the stylus contacts the faceplate. The random measurement signal frequencies reduce the susceptibility of the position measurement apparatus to electromagnetic noise and distributes over a relatively broad bandwidth the electromagnetic noise generated by the position measurement apparatus.
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Citations
22 Claims
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1. In a display system including a display surface positioned adjacent an optically transparent, electrically conductive layer having a first resistivity and first and second opposed side margins of preselected lengths, a position address encoder for generating an address signal indicative of a location on the conductive layer in contact with a stylus that is electrically connected to a reference potential, comprising:
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signal generating means for generating a time-varying position measurement signal of a preselected magnitude and a frequency that varies in a substantially random manner; first and second electrodes positioned along the lengths of the respective first and second opposed side margins and receiving the position measurement signal generated by the signal generating means, the resistivity of the conductive layer establishing an effective total resistance between the first and second electrodes; and current measuring means for measuring currents corresponding to the position measurement signal and drawn through the first and second electrodes whenever a stylus contacts the conductive layer, whereby the stylus contacting the conductive layer divides the total resistance into first and second resistances that cause currents to be drawn through the respective first and second electrodes in proportion to the separation between the electrodes and the location. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. In a display system including a display surface positioned adjacent an optically transparent, electrically conductive layer having a first resistivity and first and second opposed side margins of preselected lengths along which are positioned respective first and second electrodes, the resistivity of the conductive layer establishing an effective total resistance between the first and second electrodes, a method for generating a address signal representing a location on the conductive layer in contact with a stylus that is electrically connected to a reference potential, comprising:
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applying to the first and second electrodes a time-varying position measurement signal of substantially random frequency; and measuring currents drawn through the first and second electrodes and corresponding to the measurement signal whenever a stylus contacts the conductive layer, whereby the stylus contacting the conductive layer divides the total resistance into first and second resistances that cause currents to be drawn through the respective first and second electrodes in proportion to the separation between the electrodes and the location.
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12. In a display system including a display surface positioned adjacent and optically transparent, electrically conductive layer having a first resistivity and first and second opposed side margins of preselected lengths, a position address encoder for generating an address signal indicative of a location on the conductive layer in contact with a stylus that is electrically connectd to a reference potential, comprising:
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signal generating means for generating an amplitude modulated drive signal of a frequency that varies in a substantially random manner; first and second electrodes positioned on the respective first and second opposed side margins and receiving the input signal generated by the signal generating means, the stylus in contact with the location on the conductive layer transforming the input signal into a position measurement signal representing the location; and measurement signal demodulating means receiving the position measurement signal for demodulating it in accordance with the input signal, thereby to generate the address signal indicative of the location on the conductive layer in contact with the stylus. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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Specification