Optical touch input device
First Claim
1. An optical touch input device comprising an array of sensing elements. each of which sensing elements comprises a photosensitive device responsive to a light input from a light source, a switching device, and a charge storage means which is charred periodically by operation of the switching device, and detection means connected to the sensing elements for detecting periodically the state of charge of their charge storage means, characterised in that the photosensitive device comprises part of a discharge circuit connected to the charge storage means for discharging the charge storage means in response to a light input from a light source which discharge circuit has a light intensity dependent operational threshold characteristic such that in response to light falling on the photosensitive device which is at or above a predetermined intensity level it is operable to discharge the charge storage means and such that in response to light falling on the photosensitive device which is below said predetermined intensity level the charge storage means is not discharged, characterised in that the discharge circuit comprises a switch circuit which switches to discharge the charge storage means in response to the photosensitive element being subjected to light which is at or above the predetermined intensity level.
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Accused Products
Abstract
An optical touch input device comprises an array of actively addressed sensing elements (18) for sensing a light input, e.g. from a light pen, each of which comprises a capacitor (25) which is charged periodically through operation of a switch device (24) and a discharge circuit, including a photosensitive device (28) and a further switch device (27) connected across the capacitor, which circuit in operation demonstrates an optical threshold characteristic whereby the capacitor (25) is discharged in response to the sensing elements being subjected to light which is at or above a predetermined intensity level so as to discriminate from ambient light. Elements written into are determined by detecting the charge stage of their capacitors. The sensing element array can be integrated with a matrix display device with the sensing elements (18) and display elements components (12) provided on a common support using thin film technology.
264 Citations
10 Claims
- 1. An optical touch input device comprising an array of sensing elements. each of which sensing elements comprises a photosensitive device responsive to a light input from a light source, a switching device, and a charge storage means which is charred periodically by operation of the switching device, and detection means connected to the sensing elements for detecting periodically the state of charge of their charge storage means, characterised in that the photosensitive device comprises part of a discharge circuit connected to the charge storage means for discharging the charge storage means in response to a light input from a light source which discharge circuit has a light intensity dependent operational threshold characteristic such that in response to light falling on the photosensitive device which is at or above a predetermined intensity level it is operable to discharge the charge storage means and such that in response to light falling on the photosensitive device which is below said predetermined intensity level the charge storage means is not discharged, characterised in that the discharge circuit comprises a switch circuit which switches to discharge the charge storage means in response to the photosensitive element being subjected to light which is at or above the predetermined intensity level.
Specification