Currently, capacitive touch screens are widely applied in various electronic products such as smart phones and tablet computers. With the popularization and application of electronic terminals, the size of capacitive touch screens continues to increase, ranging from 2 to 3.5 inches in smart phones to about 10 inches in tablet computers. Future applications of capacitive touch screens may include the smart TV interface, and integration of a touch screen and a liquid crystal display (LCD), e.g., the in-cell technology. The environment in which a capacitive touch screen is applied in an electronic product is complex, which may involve various interferences such as interferences from the LCD, from a wireless communication module or from a switched-mode power supply. By detecting the frequency band with interferences, corresponding anti-interference measures such as frequency modulation and spread spectrum can be adopted to enhance the accuracy of detecting the location of a touch on the capacitive touch screen. A common detection method for capacitive touch screens is described below.
As shown in FIG. 1, in an Indium tin oxide (ITO) overlay 10, TX<1>, TX<2>, . . . , TX<m> in the horizontal direction are the driving side (collectively referred to as TXs hereinafter), and RX<1>, RX<2>, . . . , RX<n> in the vertical direction are the receiving side (collectively referred to as RXs hereinafter). Mutual capacitance occurs between the layers of TXs and RXs of the ITO overlay. For example, a coupling capacitance CP2,2 occurs at the intersection of TX<2> and RX<2>, forming a touch detection point 11. During scanning, each time only one of the TXs 22 sends an excitation signal (e.g., in FIG. 2, TX<1> is driven by a square-wave excitation signal), and the other TXs are all driven to a fixed level (e.g., ground or power supply). For example, the TXs may be driven in the order: TX<1> −> TX<2> . . . −> TX<m>. Meanwhile, the receiving modules RXs 23 in the vertical direction all perform excitation signal detection. Once a TX 22 finishes sending the excitation signal, it is driven to the fixed level; and the RXs 23 report the detection results to storage. Then the next TX 22 starts sending an excitation signal, and the RXs 23 all start another round of detection. When all the TXs 22 have finished, the detection of a frame completes. Supposing the time for a round of detection for a TX 22 is Ts, the time for completing the detection of a frame is m*Ts, resulting in a frame rate of 1/(m*Ts). As shown in FIG. 2, RA represents a line resistance between two touch points in a TX channel, and RB represents a line resistance between two touch points in a RX channel. The resistances in TX and RX channels affect the selection for the frequency of the excitation signal. The larger the resistance in a channel, the more the time for the capacitor to be charged/discharged, causing lowered TX scan frequency, and thereby reducing the frame rate.
The sizes of capacitive touch screens in existing smart phones (e.g., 5 inches) and tablet computers (e.g., 10 inches) are relatively small. As a result, the resistance in a TX or RX channel is small, so is the number of TX channels m, which permit a high scan frequency, and thereby a high frame rate. However, for a capacitive touch screen to be used in, e.g., a smart TV with a large human-machine interface, the distance between ITO wirings is maintained while the number of TX channels m is increased significantly; as a result, TXs will be driven at a low frequency, resulting in greatly reduced frame rate. In addition, in such technologies as in-cell, in order to reduce the noise in touch detection, display (e.g., LCD) driving and touch detection are performed at different time slots, which also requires rapid TX scan. Therefore, when used in a large human-machine interface, the existing driving and detection method has the problem of increased resistances in the wirings, reduced frame rate and reduced scan speed and also fails to meet the rapidity requirement for performing display driving and touch detection at different time slots.
USPTO Backgrounds
USPTO Backgrounds