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Data processing
Dec 14, 2017

After the capacitive touch screen receives the touch signal, the touch data is converted into an electrical pulse and transmitted to the touch screen control IC for processing. The signal is first amplified by a low-noise amplifier LNA, and then sent to a DSP for data processing through analog-to-digital conversion and demodulation.

Capacitive touch screen generally M + N (M column N row) a physical capacitance touch sensor. The M + N interlaced sensors make up M * N capacitive sensing points, the capacitance of which changes as the user's finger approaches the touch screen. The sensor spacing (that is, the distance between adjacent rows or columns) is usually a few millimeters, which determines the physical resolution M * N of the touch screen.

The coordinate system between the capacitive touch screen module and the LCD module is completely different. The pixel coordinates of an LCD module are typically determined by its resolution, for example, a WVGA screen with a resolution of 800 * 480, which means 800 lines of 480 RGB pixels per line. Thus, a specific location can be determined by pixel points (x, y) in the X and Y directions. The capacitive touchscreen module, on the other hand, determines the coordinate system based on its original physical dimensions in the X and Y directions. There must be a reasonable mapping between the two coordinate systems in order to ensure the correctness of the input and output operations.

Therefore, the DSP processor of the touch screen control IC has to convert the pixel mapping between the capacitive touch screen module and the LCD module to the obtained data to ensure that the touch point of the user sensed on the touch screen is the point pointed by the user.

In addition, in order to maintain the stability of the touch coordinate, the touch screen control IC needs to further process the jitter of the touch point, including the jitter of the finger and the noise of the capacitance data, and change the filtering coefficient of the low-pass filter according to the change of the coordinates, deal with.

Finally, before passing data to the host computer, you have to use software to analyze the data and determine what functions are used for each touch. This process involves determining the size, shape, and location of the area being touched on the screen. The processor groups similar touches if necessary. If the user moves his finger, the processor calculates the difference between the start and end of the user's touch.

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