1. Field of the Invention
Embodiments of the present invention relate to touch pads or touch screens and more particularly to multi-dimensional touch pad/screen sensor arrays.
2. Relevant Background
A touch screen or touch pad is a display (interface) that can detect the presence and location of a touch within a specified area. The term “touch” generally refers to contact with the display of the device by a finger or hand. Some touch screens and/or touch pads (used synonymously herein) can also sense passive objects, such as a stylus.
Touch screens encompass a broad range of technology including resistive, surface acoustic wave, capacitive, infrared, strain gage, optical imaging, dispersive signal technology, acoustic pulse recognition, frustrated total internal reflection and diffused laser imaging. Each of these technological approaches to touch screen applications possesses advantages and disadvantages.
A capacitive touch screen includes some type of array or panel that conducts a continuous electrical current across the sensor. The sensor therefore exhibits a precisely controlled field of stored electrons in both the horizontal and vertical axes. Said differently, the sensor array achieves capacitance. The human body is also an electrical device which has stored electrons and therefore also exhibits capacitance. When the sensor's capacitance field (its reference state) is altered by another capacitance field, i.e., someone's finger, electronic circuits measure the resultant change in the characteristics of the reference field and send the information about the event to the controller or central processing unit for mathematical processing. Capacitive touch screens are not affected by outside elements and have high clarity.
FIG. 1 shows a typical two dimensional touch screen matrix as is known in the prior art. As shown an array of sensors intersects over the applicable area of interest. In this example of touch screen technology, two opposing active line arrays form a matrix or sensor grid. A first array 100 of active lines 1-11 is oriented vertically while a second array 120 of active lines 1-8 is oriented horizontally. An example of a touch 130 is illustrated in the approximate center of the matrix. As described above the capacitance of the sensor array changes from the interaction of a human finger. Sensors in the vicinity of the touch register an increase in the local capacitance level as is indicated by the capacitance histograms 140, 150 adjacent to the X and Y axes of the field, respectively. As shown the touch 130, while possessing an estimated touch location of approximately (5.6, 4.8), shows a capacitance increase on the Y axis beginning at location 3.6 and ending at location 5.6 and on the X axis beginning at approximately location 4.8 and extending to location 6.6. Using these ranges of capacitance variations, an estimated touch location is determined.
While this type of capacitance matrix or sensor array is capable of accurately determining a single touch on a touch screen, it does not possess the ability to decipher multiple (simultaneous) touches. As with many two dimensional touch screen technologies, multiple touches produce a geometrical multiple number of coordinate combinations. FIG. 2 shows a two dimensional touch screen using a X, Y grid sensor orientation as is known in the prior art. As described previously the touch screen includes a set of sensors 1-11 oriented vertically along the X axis 210 and a set of sensors 1-8 oriented horizontally along the Y axis 220. Histograms representative of capacitance levels on the horizontal array 250 and the vertical array 240 indicate the presence of a touch via raised capacitance levels.
Upon a multiple touch, in this example a dual touch, two actual touch areas 230 are created on the touch screen. At each location the sensors recognize a rise in capacitance levels and register a touch. This type of prior art system, however, can not differentiate between the actual touched areas 230 and two ghost touch areas 260. As shown on the Y axis, the horizontally oriented sensors recognize a touch at approximately (2.2, 6.2). Similarly the vertically oriented sensor array identifies a touch at (3, 9.2). Yet the real touch 230 is located at (3, 6.6) and (9.2, 2.2). The ability to differentiate the coordinates of the real touch from those identifying locations (3, 2.2) and (9.2, 6.2) remains a challenge. Embodiments of the present invention address these and other challenges in the prior art.