Patent ID: 7714846
Filing Date: 2010-05-11
Classification: G06F

Abstract:
1. A touchscreen system, comprising: a touchscreen having a frontside and a backside; a resistive pattern that is attached to the backside of the touchscreen; a plurality of drive signal circuits that are communicatively coupled to the resistive pattern at communicative coupling points, each drive signal circuit within the plurality of drive signal circuits is also operable to measure current flow at the communicative coupling points of each drive signal circuit within the plurality of drive signal circuits to the touchscreen; wherein each drive signal circuit within the plurality of drive signal circuits operates cooperatively to energize the resistive pattern thereby generating an amplitude ramped field that communicatively couples through the touchscreen to the frontside of the touchscreen and extends across the frontside of the touchscreen in a direction, the direction being selectable by applying full scale AC signals to some of the communicative coupling points and virtual ground signals to other communicative coupling points, the amplitude ramped field is operable to be selectively ramped in a plurality of directions across the touchscreen; a plurality of subtraction circuits, each subtraction circuit being communicatively coupled to one of the plurality drive signal circuits and each subtraction circuit being operable to remove any substantially purely resistive current portion that is injected into one of the corners by one of the drive signal circuits, each of the subtraction circuits also being operable to perform high pass filtering and adding to remove any resistance portion of the current flow at the corners of the touchscreen thereby leaving a resulting current flow having an unbalanced capacitive reactance current portion; a nulling and adding circuitry that is operable to reduce a non-user touch portion of the unbalanced capacitive reactance current portion and to increase an overall resolution of the unbalanced capacitive reactance current portion that is substantially attributable to a user's touch on the touchscreen; an analog to digital converter that converts the unbalanced capacitive reactance current portion that is substantially attributable to a user's touch on the touchscreen to a digital signal; wherein the current flow at the points of communicative coupling includes an unbalanced capacitive reactance current portion wherein a change of the unbalanced capacitive reactance current portion includes a portion that is substantially attributable to a user's interaction or touch on the touchscreen; and a digital signal processor that is operable to process a digital version of the change of the unbalanced capacitive reactance current portion to discriminate a location of the user's interaction or touch on the touchscreen.