Depending on sensing signal detecting modes of capacitive touch panels, the capacitive touch panels include self capacitive touch panels and mutual capacitive touch panels.
As shown in FIG. 1, a mutual capacitive touch panel contains a plurality of driving lines (for example Y1 to Y4) and a plurality of sensing lines (for example X1 to X4) intersecting with the driving lines. A sub-pixel of the touch panel is surrounded by a dashed box. A capacitance caused by the overlapping portions of the driving line and the sensing line will not be influenced by an external touching object, but will cause a steady background noise or a Direct Current (DC) component inputted to a preamplifier A. However, a mutual capacitance Cm that is formed by a spatial fringe electric field generated between the non-overlapped portions of electrodes of the driving lines and the sensing lines will be influenced directly by the external touching objects.
An equivalent circuit of a typical mutual capacitive touch panel as shown in FIG. 1 works in principle as described simply as follows: driving signals with a specific frequency are inputted one by one through ends of the driving lines, and signals with the same frequency induced by the mutual capacitance Cm between the driving lines and the sensing lines are received and amplified by the preamplifier A connected to ends of the sensing lines. When the surface of the touch panel is touched by a finger of a user, parasitic capacitances are formed between the finger and the driving lines and between the finger and the sensing lines. A portion of the signals will be directly leaked to the ground through the user's body or the grounded object via the parasitic capacitance, thus the signals received by the preamplifier A are previously attenuated. Depending on the design for the electrode of the touch panel, the driving frequency and the distance between the user's finger and the electrode of the touch panel, the driving signals might be coupled from the driving lines to the sensing lines through a medium such as the user's finger, thereby the signals received by the preamplifiers A are increased. In both signal induction modes, a specific position touched by the finger T can be easily found out by detecting the signal changes in the sensing lines one by one.
In the prior art, driving signals with a specific frequency are inputted one by one to the input ends of the driving lines. When a finger touches the touch panel, the mutual capacitance between the driving line and the sensing line is changed so that the amplitude of the signal of the specific frequency received from the sensing line by a detection device is varied accordingly. Each of such driving signals of a specific frequency is necessarily inputted to each of the driving lines, that is, the driving lines are scanned by specific pulse signals. According to this method in the prior art, the circuitry becomes very complicated and costly in the case of a large number of the driving lines or the high-speed detection.
USPTO Backgrounds
USPTO Backgrounds