How does surface capacitive touch technology drive a new revolution in human-machine interfaces? （1） 3

touch point and enhancing recognition accuracy. By copying the aforementioned pattern several times in the X-axis and Y-axis directions (the number of times depends on the screen size), a PCT matrix similar to a keyboard is formed. Figure 1 is currently the most common diamond pattern.

Figure 1: Diamond pattern layout of projected capacitive screen.  diode

The orange diamond pattern in Figure 1 forms m ITO wires in the X-axis direction, while the green diamond pattern forms n ITO wires in the Y-axis direction; The PCT controller will sequentially drive these wires to detect whether there is an increase in capacitance due to touch.

Figure 2: PCT equivalent RC circuit and detection waveform on X2 wire before and after finger touch.

Taking the simplest RC oscillation scheme as an example. We simplify the equivalent circuit of the X2 wire in the X-axis as shown in Figure 2, forming an RC circuit consisting of n Rp and n Cp, where Rp and Cp represent the equivalent ITO segment internal resistance and the intrinsic capacitance values of each node (XY axis intersection) of PCT, respectively. When the finger approaches or touches the screen, it will increase a capacitance (Cf) on the screen; For this RC oscillation circuit, the appearance of Cf means that the oscillation period becomes longer and the frequency decreases. By calculating the oscillation period and frequency changes on the X2 wire before and after finger touch, the PCT controller can identify the touch location and even distinguish the distance between the finger and the screen (i.e. provide Z-axis information).  diode