The data processing process of capacitive touch-screen

- Jul 19, 2018-

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 amplified by a low noise amplifier lna, then through analog-to-digital conversion and demodulation, finally sent to a DSP for data processing. Capacitive touch screen usually has m+n (M column N line) a physical capacitive touch sensor. This m+n sensor makes up the m*n capacitance sensor, which changes as the user's finger approaches the touch screen. 

The sensor interval (i.e., the distance between adjacent rows or columns) is usually around a few millimeters, which determines the physical resolution of the touchscreen m*n. The coordinate system between the capacitive touch screen module and the LCD module is completely different. The pixel coordinates of the LCD module are generally determined by its resolution, for example, a WVGA screen with a resolution of 800*480, that is, 800 rows, 480 RGB pixels per line. Thus, a specific position can be determined by pixels (x,y) in the X and y directions. The capacitive touchscreen module determines the coordinate system according to its original physical dimensions in the direction of X and Y. 

A reasonable mapping method must exist between the two coordinate systems to guarantee the correctness of the input and output operation.

Therefore, the touch-screen control IC DSP processor also has to be the data to the Capacitive touch screen module and LCD module pixel mapping between the conversion, so as to ensure that the touch screen sensor to the user's touch point is the point of the user. 

In addition, in order to maintain the stability of the touch coordinate, the touch-screen control IC needs to further deal with the jitter of the touch point, including the jitter of the finger and the noise of the capacitance data, and change the filter coefficients of low-pass filter According to the change of the coordinates, and realize the smoothing of the coordinates Finally, before uploading the data to the host, it is necessary to use software analysis data to determine what function each touch is intended to use. This process involves determining the size, shape, and location of the area that is touched on the screen. If necessary, the processor groups similar touch-sorting. If the user moves the finger, the processor calculates the difference between the starting and ending points of the user's touch.