Preventing noise in a coordinate input device by reducing or suspending backlight oscillation voltage
First Claim
1. A coordinate input device comprising:
- a liquid crystal panel including a liquid crystal layer between a plurality of segment electrodes and a plurality of common electrodes orthogonal to each other;
a light source for directing light uniformly from a back side of said liquid crystal panel;
an inverter power source for driving said light source;
electrode driving means for driving said segment electrodes and said common electrodes;
display control means for controlling said electrode driving means during a display period to display an image on said liquid crystal panel;
a position detection pen for electrostatically coupling said segment electrodes and said common electrodes;
position detection control means for controlling said electrode driving means during a position detection period set subsequent to a display period to apply a scanning voltage sequentially;
coordinate calculation means for calculating coordinates according to an induced voltage induced at said position detection pen and the timing of applying the scanning voltage to said segment electrodes; and
power source drive suspension means for suspending the drive of said light source by said inverter power source only during said position detection period.
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Abstract
A d.c. voltage is supplied to an inverter power source to drive a light source. Light from the light source is directed uniformly from the back side of a liquid crystal panel. When an image is displayed on the liquid crystal panel during a display period and a position detection pen is in close proximity to the liquid crystal panel at a position detection period, coordinates are calculated according to an induced voltage by the position detection pen and the timing of applying a scanning voltage to an electrode of the liquid crystal panel. The driving of the light source by the inverter power source is suspended or reduced during the position detection period, so that noise from the inverter power source is prevented from being mixed into the position detection pen.
67 Citations
14 Claims
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1. A coordinate input device comprising:
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a liquid crystal panel including a liquid crystal layer between a plurality of segment electrodes and a plurality of common electrodes orthogonal to each other; a light source for directing light uniformly from a back side of said liquid crystal panel; an inverter power source for driving said light source; electrode driving means for driving said segment electrodes and said common electrodes; display control means for controlling said electrode driving means during a display period to display an image on said liquid crystal panel; a position detection pen for electrostatically coupling said segment electrodes and said common electrodes; position detection control means for controlling said electrode driving means during a position detection period set subsequent to a display period to apply a scanning voltage sequentially; coordinate calculation means for calculating coordinates according to an induced voltage induced at said position detection pen and the timing of applying the scanning voltage to said segment electrodes; and power source drive suspension means for suspending the drive of said light source by said inverter power source only during said position detection period. - View Dependent Claims (2, 3, 4)
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5. A coordinate input device comprising:
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a liquid crystal panel including a liquid crystal layer between a plurality of segment electrodes and a plurality of common electrodes orthogonal to each other; a power source for directing light uniformly from a back side of said liquid crystal panel; an inverter power source for driving said power source; electrode driving means for driving said segment electrodes and said common electrodes; display control means for controlling said electrode driving means during a display period for displaying an image on said liquid crystal panel; a position detection pen for electrostatically coupling said segment electrodes and said common electrodes; position detection control means for controlling said electrode driving means during a position detection period set subsequent to a display period to apply a scanning voltage sequentially; coordinate calculation means for calculating coordinates according to an induced voltage induced in said position detection pen and the timing of applying the scanning voltage to said segment electrodes; and voltage reducing means for reducing an oscillation voltage of said inverter power source only during said position detection period. - View Dependent Claims (6, 7)
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8. A method for reducing noise in a coordinate input device comprising the steps of:
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placing a liquid crystal layer between a plurality of segment electrodes and a plurality of common electrodes orthogonal to each other; directing light uniformly from a back side of said liquid crystal panel from a light source; driving said segment electrodes and said common electrodes; controlling said driving step during a display period to display an image on said liquid crystal panel; electrostatically coupling said segment electrodes and said common electrodes via a position detection pen; controlling said driving step during a position detection period set subsequent to a display period to apply a scanning voltage sequentially; calculating coordinates according to an induced voltage induced at said position detection pen and the timing of applying the scanning voltage to said segment electrodes; and suspending said directing step only during said position detection period. - View Dependent Claims (9, 10, 11)
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12. A method for reducing noise in a coordinate input device comprising the steps of:
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placing a liquid crystal layer between a plurality of segment electrodes and a plurality of common electrodes orthogonal to each other; directing light uniformly from a back side of said liquid crystal panel from a light source; driving said segment electrodes and said common electrodes; controlling said driving step during a display period for displaying an image on said liquid crystal panel; electrostatically coupling said segment electrodes and said common electrodes via a position detection pen; controlling said driving step during a position detection period set subsequent to a display period to apply a scanning voltage sequentially; calculating coordinates according to an induced voltage induced in said position detection pen and the timing of applying the scanning voltage to said segment electrodes; and reducing power supplied by said light source only during said position detection period. - View Dependent Claims (13, 14)
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Specification