Method for operating touch-screen system

Abstract

A method and apparatus are provided for adapting an acoustic touch screen controller to the operating frequency requirements of a particular touch screen. The adaptive controller can use a lookup table to obtain the desired output frequency or can employ a multi-step process where the frequency requirements of the touch screen are first determined and then the burst frequency characteristics, receiver circuit center frequency, or both are adjusted according to the touch screen requirements. In one embodiment, the adaptive controller compensates for global frequency mismatch errors. In this embodiment, a digital multiplier is used to modify the output of the crystal reference oscillator. The reference oscillator output is used to control the frequency of the signal from the receiving transducer and / or to generate the desired frequency of the audio burst sent to the transmitting transducer. In another embodiment designed to compensate for both global and local frequency variations, the adaptive controller employs a digital signal processor. Based on correction values ​​contained in memory, the digital signal processor defines a particular center frequency that preferably varies according to signal delay, thereby accounting for variations caused by local variations in the acoustic reflective array. In yet another embodiment, an amorphous local oscillator is used to provide the reference signal in the adaptive controller. Using such an oscillator enables the controller to be miniaturized enough to be mounted directly to the touch screen substrate. A feedback loop is employed to compensate for oscillator drift. A frequency discriminator circuit determines the degree of deviation from the desired frequency. Use the output of the discriminator to adjust the frequency of the local oscillator so that it tracks the frequency of the touch screen.

Description

Technical field [0001] The present invention generally relates to a touch screen, and more specifically, to a method and device for adjusting the frequency of a touch screen controller so as to match the controller with the specific operating characteristics of a specific touch screen. Background technique [0002] The touch screen cooperates with various display types, including cathode ray tube (ie CRT) and liquid crystal display (ie LCD screen), as a device for inputting information into the data processing system. When the touch screen is placed on the display screen or integrated into the display screen, the user can select the displayed icon or element by touching the position corresponding to the target icon or element on the screen. In various applications, including, for example, point-of-sale systems, information kiosks, automatic teller machines (ie ATM), data entry systems, etc., touch screens have become commonplace. [0003] In a specific type of touch screen, acous...

AI Technical Summary

Problems solved by technology

[0008] Global or local frequency mismatches can be caused by different sources

While some sources of mismatch can be overcome with adequate quality control, such controls are often costly

For example, variations in touch screen glass substrates may alter the acoustic velocity, resulting in a global frequency mismatch, and it may not be economically feasible to adequately control the glass supply chain and manufacturing process to ensure that the acoustic velocity of all substrates is within a narrow range

Controlling the glass supply chain and manufacturing process is even more problematic when the acoustically reflective array is printed directly onto the faceplate of a cathode ray tube (i.e. CRT)

Print mask distortion is especially problematic if the array is to be printed directly onto a CRT panel

Other array printing techniques such as embossing also suffer from registration errors introduced during the printing process, which can lead to further frequency mismatches

Yet another source of frequency mismatch can come from improper correction for spherical geometry effects on non-planar substrate surfaces

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