While the iPhone was being introduced back in January 2007 by Steve Jobs, Apple had already invented their Next Generation Touch Technology for their future iPad. Apple's granted patent, which was published earlier today, shows us that multi-touch technology for tablet PC's had to be different than that for the iPhone. Apple was clearly well ahead of the curve on this technology and on course for delivering the iPad three years later.
Apple Wins a Patent for a Digital Controller for a True Multi-Point Touch Surface Useable in a Computer System
As Steve Jobs was providing us with a peek at the coming iPhone, they were already deeply engaged in developing next generation true multi-point touch surfaces for the iPad. Apple's patent discusses the problems with the first generation multi-touch technologies as they related to tablets. The iPhone was a smaller surface and so their multi-touch technology was just fine.
To make this point, Apple's patent states that "one problem found in these prior art technologies – is that they are only capable of reporting a single point even when multiple objects are placed on the sensing surface. That is, they lack the ability to track multiple points of contact simultaneously. In resistive and traditional capacitive technologies, an average of all simultaneously occurring touch points are determined and a single point which falls somewhere between the touch points is reported. In surface wave and infrared technologies, it is impossible to discern the exact position of multiple touch points that fall on the same horizontal or vertical lines due to masking. In either case, faulty results are generated.
These problems are particularly problematic in handheld devices, such as tablet PCs, where one hand is used to hold the tablet and the other is used to generate touch events."
Apple's newly Granted Patent relates to an improved touch surface controller for controlling a multi-point touch surface such as a touch screen or a touch pad in computer systems. The improved touch system controller detects signal capacitance from the pixels in the touch surface digitally, and therefore is easier and simpler to implement then previous approaches relying on analog detection and processing.
Specifically, signal capacitance is measured by measuring a number of clock cycles taken to discharge or charge the input node of a comparator. Embodiments of the disclosed touch surface controller are particularly useful in the context of detecting multiple simultaneous touches on the touch surface.
Apple's patent FIG. 1 shown above illustrates an array of pixels in a touch surface, related detection circuitry, and the interfacing with a system microprocessor; Patent FIG. 4 illustrates an improved touch surface controller in accordance with an embodiment of the invention, which in particular includes digital detection circuitry.
Apple's First Claim: A controller for a touch surface having a plurality of capacitive pixels, each capacitive pixel having a first electrode and a second electrode, different from the first electrode and defining a pixel capacitance therebetween, the controller comprising: stimulation circuitry for applying a stimulation voltage having a first and second voltage level to only the first electrode of at least some of the plurality of capacitive pixels, a plurality of detection circuits, one detection circuit corresponding to each channel defined as a group of capacitive pixels arranged along a given direction; each detection circuit comprising: input circuitry having an input node capable of being coupled to the second electrode of the at least some of the plurality of capacitive pixels for detecting the pixel capacitance of the at least some of the plurality of capacitive pixels, wherein a change in the pixel capacitance at a given pixel indicates proximity of a touch to that pixel: charging and discharging circuitry for alternately charging the capacitive pixels to a reference voltage after the stimulus voltage of the first voltage level is applied to the first electrode of the capacitive pixels, and discharging the capacitive pixels to the reference voltage after the stimulus voltage of the second voltage level is applied to the first electrode of the capacitive pixel; the charging and discharging circuitry generating a hold signal indicating whether a charging or discharging of the capacitive pixels is in progress; and counting circuitry for digitally counting at least one of a charging time period to charge the capacitive pixels to the reference voltage and a discharging time period to discharge the capacitive pixels to the reference voltage, each of the charging time period and the discharging time period indicative of pixel capacitance of the at least some of the plurality of capacitive pixels; wherein the hold signals from each channel are logically combined to indicate whether a charging or discharging of the capacitive pixels is in progress for any channel and wherein the stimulation circuitry is prevented from applying another stimulation voltage until the logically combined hold signals indicates that all channels have completed their respective charging and discharging.
To review Apple's other 32 important patent claims and other detailing, see granted patent 8,054,299. Apple credits Christopher Krah as the sole inventor of this patent which was originally filed in January 2007.
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