Touch Screen Element

Abstract

A capacitive two-dimensional (2D) touch panel has three sets of interleaved electrodes. A first set of electrodes is spaced apart along the y-direction and these are galvanically connected to each other by a resistive strip connected at either end to a connection line. A second set of electrodes is also arrayed along the y-direction and these are galvanically connected to each other via a notionally non-resistive first connection. A third set of electrodes is also arrayed along the y-direction and these are galvanically connected to each other via a notionally non-resistive second connection. The second and third sets of electrodes are interleaved without galvanic cross-conduction to provide a gradient along the x-direction to resolve touch position in the x-direction. The first set of electrodes resolves touch position along the y-direction. Passive or active capacitive sensing techniques may be used to acquire the position information from the 2D touch panel.

Description

BACKGROUND OF THE INVENTION[0001]The invention pertains to 2-dimensional touch sensing surfaces operable by a human finger, or a stylus. Example devices include touch screens and touch pads, particularly those over LCDs, CRTs and other types of displays, or pen-input tablets, or encoders used in machinery for feedback control purposes. In particular this invention pertains to 2-dimensional capacitive touch sensing surfaces constructed so that the sensing layer is disposed on the rear of a panel or lens surface, particularly for use in smaller touch screens where there is a space constraint along the edges of the screen, for example in portable devices such as mobile phones or handheld media players. In addition the invention addresses the need to reduce the effects of capacitive ‘hand shadow’.[0002]In my earlier co-pending U.S. application Ser. No. 10 / 916,759 (published as US2005 / 0041018A), there is a pattern of galvanically coupled conductors which have anisotropic galvanic propert...

AI Technical Summary

Benefits of technology

[0033]Another object of the invention is to provide for a driver circuit having low average power, for example by the use of sleep modes where the device samples slowly or not at all and mostly sleeps, and a wake function whereby when touched the device speeds up to provide appropriate speed of response.

[0034]Another object of the invention is to provide for proximity detection, so that the sensing surface can be made to react to non-touch, for example to provide a wakeup function for the product it is interfaced to, to bring it out of a low-power sleep state.

Problems solved by technology

Many types of 2DCT are known to suffer from a geometric distortion known as ‘pin-cushion’ whereby the reported coordinate of touch is in error due to electrical effects on the sensing surface.

U.S. Pat. No. 4,550,221 (Mabusth) is an example of a matrix approach where x and y oriented electrodes must cross each other, forcing the electrode structure to occupy two or more layers which adds considerable expense and in the case of LCD touch screens reduces transparency.

Co-pending U.S. Provisional Application 60 / 697,613 (published as GB2428306) further describes a method for structuring electrodes which avoid crossovers in the sensing region with little or no distortion, but this method still requires a relatively large number of connections.

These methods can all provide good resolution but require a large number of connections and are therefore costly to implement.

Also, a high connection count limits utility in smaller touch screens were there is little space surrounding the sensing area to permit large numbers of wiring traces to the connections.

2DCT devices which employ matrix or electrode-to-electrode coupling approaches such as U.S. Pat. No. 4,198,539 (Pepper) or U.S. Pat. No. 5,650,597 (Redmayne) also have a limited ability to project fields through thick materials, or to project their fields slightly into free space to create a ‘point screen’.

In the case of U.S. Pat. No. 4,198,539 (Pepper) the individual electrodes are very narrow and as a result have limited surface area which is essential to project a field through a thicker dielectric; as a result, such designs are typically limited in application to track pads for notebook computers and the like, with a thin overlay on top of electrodes.

Such limitations reduce touch signal strength and prevent the use of the electrodes with thick dielectric layers.

Such a calibration process adds to the cost of the sensing element and can easily fall out of calibration with time and environmental conditions, such as temperature or humidity or exposure to light, which over time can alter the resistance of the electrodes.

The need for recalibration of the sensing element is a serious commercial disadvantage.

The device cannot therefore detect a human touch.

One disadvantage of the y axis field gradient produced by this design is that the gain along the vertical axis is insufficient to provide full scale readings, thus requiring the output to be rescaled accordingly.

Also it is quite difficult to prevent the response from being granular as the patterns can be quite large to accomplish the desired gradient effect on the y axis.

This system is also incapable of detecting human touch.

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