Data Processing Process Of Capacitive Touch Screen

After receiving the touch signal, the capacitive touch screen converts the touch data into electrical pulses and transmits them to the touch screen control IC for processing. The signal is first amplified by a low noise amplifier LNA, then subjected to analog-to-digital conversion and demodulation, and finally sent to a DSP for data processing.
Capacitive touch screens generally have M+N (M columns and N rows) physical capacitive touch sensors. These M+N interconnected sensors form M * N capacitive sensing points, and their capacitance changes as the user's fingers approach the touch screen. The spacing between sensors (i.e. the distance between adjacent rows or columns) is usually around 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 generally determined by its resolution. For example, a WVGA screen has a resolution of 800 * 480, which means there are 800 rows of 480 RGB pixels per row. Thus, a specific position can be determined by the pixels (x, y) in the X and Y directions. The capacitive touch screen module determines the coordinate system based on its original physical dimensions in the X and Y directions. There must be a reasonable mapping method between two coordinate systems to ensure the correctness of input and output operations.
So, the DSP processor of the touch screen control IC also needs to perform pixel mapping conversion between the capacitive touch screen module and the LCD module to ensure that the user's touch point is sensed on the touch screen as the point pointed by the user.
In addition, in order to maintain the stability of the touch coordinates, the touch screen control IC needs to further handle the shaking of the touch points, including finger shaking and capacitance data noise, and change the filtering coefficient of the low-pass filter according to the changes in coordinates to achieve smooth processing of the coordinates.
Finally, before transferring the data to the host, software needs to be used to analyze the data and determine what functions each touch is intended to use. This process involves determining the size, shape, and position of the touched area on the screen. If necessary, the processor will organize and group similar touches. If the user moves their fingers, the processor calculates the difference between the starting and ending points of the user's touch.