The projected capacitive touch screen senses touch by scanning. In other words, it measure each independent electrode or electrode intersection one by one in a cyclic scanning manner. Since each electrode individually connect to the controller, the self-capacitive touch screen adopts a simple sequential scanning method. This is self-capacitive touchscreen scanning method.
And mutual capacitance touchscreen scanning method is like this.The mutual capacitive touch screen uses a more complex scanning mechanism. In the other words, it measure each pair of intersecting electrodes in all permutations and combinations. This type of scanning is usually called full-point addressing, and the controller drives a column as drive electrodes. Then scan all horizontal rows (Z) as sensing electrodes to measure the capacitance value. After completion, drive the next column of 00, and then scan all U) to measure the capacitance value. After scanning each column, the whole scene starts again.
This makes the processor load of the mutual capacitive touch screen relatively high. But it supports true multi-touch. At present, the scan rate range of the projected capacitive touch screen processor is about 20 ~ 200HZ (that is, 5 ~ 50ms per field). Press the 3.5in smart phone touch screen has 9 columns and 16 rows. So each field needs to scan 144 pairs of capacitors.
Among the two types of projected capacitive touch screens. In order to calculate the precise touch position. It is necessary to comprehensively calculate the continuous change of the capacitance value of the adjacent electrode or cross electrode pair. Used to insert precise touch coordinates. The result of this is accurate and M higher resolution, up to 1024 x1024 (lObit). There is another advantage of scanning, which is to prevent drift. Because the electrode limit the drift to each small area formed . It also solves the drift problem. As long as it is securely connected to the display, the projected capacitive touch screen no longer requires end-user calibration.
In the case of normal and single-point touch, the self-capacitance scan mode is activated. Give full play to its advantages of fast scanning speed and simple algorithm. In the case of multi-finger touch, the mutual capacitance scanning mode is activated. Give full play to its advantages of being able to recognize multiple real points. Both self-capacitance and mutual-capacitance scanning methods have their own advantages and disadvantages. A mature solution will combine the advantages of self-capacitance and mutual capacitance. Give full play to their respective advantages, while shielding their respective shortcomings.
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