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Researchers Submit Patent Application, "Touch Acquisition in a Projected Capacitive Touch Screen System", for Approval

July 30, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Teissier, Maxime (Tokyo, JP); Troise, Cyril (Marseille, FR), filed on January 8, 2013, was made available online on July 17, 2014.

The patent's assignee is Stmicroelectronics (rousset) Sas.

News editors obtained the following quote from the background information supplied by the inventors: "Touch screens are common technologies in today's electronic devices. There are three common touch screen configurations: resistive touch screens, surface capacitive touch screens and projected capacitive touch screens.

"Reference is now made to FIG. 1 which illustrates a conventional projected capacitive touch screen system 10. The system 10 includes a touch screen panel 20 and a touch screen circuit 30. The touch screen panel 20 supports a layout of electrodes. The electrodes include a plurality of first electrodes 22 extending in a first direction (for example, a vertical direction) and a plurality of second electrodes 24 extending in a second direction (for example, a horizontal direction) such that the first electrodes and second electrodes cross each other at intersection locations 26. The plurality of first electrodes 22 are provided on a first layer of the touch screen panel 20 and the plurality of second electrodes 24 are provided on a second layer of the touch screen panel. The first and second layers of the touch screen panel 20 are separated from each other by an insulating layer (not explicitly shown), and thus a capacitance is formed at each intersection location 26 between one first electrode 22 and one second electrode 24. The touch screen panel 20 may further include, in a manner understood by those skilled in the art, a number of other supporting and protecting layers.

"The touch screen processing circuit 30 includes a plurality of transmit drive circuits 32 and a plurality of receive sense circuits 34. The outputs of the transmit drive circuits 32 are coupled to the plurality of first electrodes 22, while the inputs of the receive sense circuits 34 are coupled to the plurality of second electrodes 24. Sensing of the touch screen panel 20 is performed under the control of the processing circuit 30 by scanning the intersection locations 26 to sense capacitance. This is accomplished by activating one of the transmit drive circuits 32 and one of the receive sense circuits 34 whose corresponding first electrode 22 and second electrode 24 intersect at the desired location 26 to be scanned. The sensed capacitance at each location 26 is varied under the influence of a touch made to (or near) the panel 20. The scanning operation is repeated for each location 26 within the panel 20. Thus, it will be understood that a total of XY scanning operations must be performed in order to completely scan all intersection locations 26 of the touch screen panel 20 (where X is the number of column electrodes and Y is the number of row electrodes).

"An example of a suitable touch screen processing circuit 30 for use with a projected capacitive touch screen panel 20 is the STM8T family of microcontrollers produced by STMicroelectronics, for example, the STM8TL53 microcontroller. This microcontroller includes, for example, up to fifteen transmit drive circuits 32 (transmit channels) and up to twenty receive sense circuits 34 (receive channels).

"The scanning operation performed by the touch screen processing circuit 30 permits the resolution of multiple simultaneous touches being made to the panel 20 along the an identification of the X and Y coordinates of each touch.

"As touch screen panels increase in size, the length of the first electrodes 22 and second electrodes 24 also increases. With increased electrode length, there is a corresponding increase in electrode resistivity. The increase in electrode resistivity produces an increase in the RC time constant of the drive and sense circuit, and the increased RC time constant results in an increase in the acquisition time for each scan of an intersection location 26. Still further, with increased sized touch screen panels there is an increase in the number of first electrodes 22 and second electrodes 24 that are needed, and thus the number of intersection locations 26 to be scanned also increases. The increased acquisition time for each location scan is magnified by the increased number of scanned locations resulting in an unacceptable scanning operation for the projected capacitive touch screen system.

"Reference is now made to FIG. 2 which illustrates a conventional surface capacitive touch screen system 50. The system 50 includes a touch screen panel 60 and a touch screen processing circuit 70. The touch screen panel 60 supports a layout of electrodes. The electrodes include a plurality of first electrodes 62 extending in a first direction (for example, a vertical direction) and a plurality of second electrodes 64 extending in a second direction (for example, a horizontal direction). The electrodes 62 and 64 are provided on one or more layers of the touch screen panel 60. A transparent electroconductive layer (not explicitly shown) is provided over the first layer.

"The touch screen processing circuit 70 includes a plurality of sensing circuits 72, each having a node coupled to one of the electrodes 62 and 64. Each sensing circuit generates an AC sensing signal (for example, an AC square wave or sinusoidal voltage signal) which is applied to the electrodes 62 and 64. Current flowing in the electrodes 62 and 64 as a result of the applied AC sensing signals is varied under the influence of a touch made to the surface of the panel 60. Ground return for the signals is made through the earth or body of the person touching the panel. A resulting change in capacitance is sensed by the sensing circuits 72 and resolved to calculate the X and Y coordinates of the touch. In order to scan the entire panel, X+Y sensing acquisitions must be made (where X is the number of column electrodes and Y is the number of row electrodes) by the circuits 72. This is significantly less than the XY scanning operations that must be performed in the projected capacitive system of FIG. 1, and thus the acquisition time in the surface capacitive touch screen system is relatively quick even with significantly large panel sizes.

"It is accordingly common to use projected capacitive touch screen systems in mobile applications such as cellular telephones where the panel size is relatively small. It is also common to use surface capacitive touch screen systems in fixed applications such as computer interactive graphical user interface displays of larger size.

"There would be an advantage if projected capacitive touch screen systems could be configured to provide a surface capacitive-like acquisition at least in terms of acquisition time thus enabling projected capacitive touch screen panels and processing circuits to be used in connection with larger sized panels."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "In an embodiment, an apparatus comprises: a capacitive touch panel including a plurality of first electrodes extending in first direction and a plurality of second electrodes extending in a second direction, the first and second electrodes intersecting each other; wherein the plurality of first electrodes includes transmit first electrodes and receive first electrodes, the transmit first electrodes and receive first electrodes being interleaved; wherein the plurality of second electrodes includes transmit second electrodes and receive second electrodes, the transmit second electrodes and receive second electrodes being interleaved; transmit circuitry coupled to the transmit first electrodes and transmit second electrodes; and receive circuitry coupled to the receive first electrodes and receive second electrodes.

"In an embodiment, a method, comprises: controlling operation of a capacitive touch panel including a plurality of first electrodes extending in first direction and a plurality of second electrodes extending in a second direction, the first and second electrodes intersecting each other; wherein the plurality of first electrodes includes transmit first electrodes and receive first electrodes, the transmit first electrodes and receive first electrodes being interleaved; wherein the plurality of second electrodes includes transmit second electrodes and receive second electrodes, the transmit second electrodes and receive second electrodes being interleaved; wherein controlling comprises: activating transmit circuitry coupled to the transmit first electrodes and transmit second electrodes; and activating receive circuitry coupled to the receive first electrodes and receive second electrodes.

"In an embodiment, a capacitive touch panel includes: first electrodes extending in first direction; second electrodes extending in a second (intersecting) direction; wherein the first electrodes include parallel extending transmit first electrodes and receive first electrodes that are interleaved with each other; wherein the second electrodes include parallel extending transmit second electrodes and receive second electrodes that are interleaved with each other; transmit circuitry coupled to the transmit first electrodes and transmit second electrodes; receive circuitry coupled to the receive first electrodes and receive second electrodes; and processing circuitry which controls activation of the transmit and receive circuitry in a manner which supports the making of adjacent line capacitance measurements and intersecting line capacitance measurements and the processing of the capacitance measurements to identify and determine location of touches made on or near the capacitive touch panel.

BRIEF DESCRIPTION OF THE DRAWINGS

"For a better understanding of the embodiments, reference will now be made by way of example only to the accompanying figures in which:

"FIG. 1 illustrates a conventional projected capacitive touch screen system;

"FIG. 2 illustrates a conventional surface capacitive touch screen system;

"FIG. 3 illustrates an embodiment of a projected capacitive touch screen system;

"FIGS. 4A-4D illustrate a process for scanning performed by the system of FIG. 3;

"FIGS. 5A and 5B illustrate single touch and multi-touch scenarios for the scanning process;

"FIG. 6 illustrates an embodiment of a projected capacitive touch screen system;

"FIGS. 7A-4F illustrate a process for scanning performed by the system of FIG. 6; and

"FIGS. 8A and 8B illustrate single touch and multi-touch scenarios for the scanning process."

For additional information on this patent application, see: Teissier, Maxime; Troise, Cyril. Touch Acquisition in a Projected Capacitive Touch Screen System. Filed January 8, 2013 and posted July 17, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4175&p=84&f=G&l=50&d=PG01&S1=20140710.PD.&OS=PD/20140710&RS=PD/20140710

Keywords for this news article include: Electronics, Microcontroller, Stmicroelectronics (rousset) Sas.

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Source: Electronics Newsweekly


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