Many capacitive touch panels or capacitive touch screens employ projected capacitive sensing to determine touch locations. Generally, each touch sensor within the touch panel is comprised of a two electrodes under a transparent plate (i.e., plastic), and, when a dielectric (i.e., finger) is in proximity to the two plates (with one plate being an excitation plate and one being a detection plate), the capacitance between the two plates decreases. In order to determine the location of the touch event (i.e., where the finger increases capacitance), the touch screen controller will usually “scan through” the excitation and detection plates and calculated the position of the touch event. One problem with these systems, however, is noise. Usually, the touch events result in about 0.1 pF of increased capacitance, and a finger can inject noise when touching the panel (i.e., 60-cycle noise). Thus, the touch event can be lost in the noise. Therefore, there is a need for an improved touch panel controller.
Some other examples of conventional circuits are: U.S. Pat. Nos. 5,526,294; 5,565,658; and 6,366,099.