Structures and Categories of Capacitive Touch Screen

As a kind of intelligent man-machine interface, capacitive touch screen is widely used. It is characterized by low power consumption, long service life, stable operation and simple operation. So what is the structure of the capacitive touch screen? How does it work? What are the specific categories?

Ⅰ. The structure of capacitive touch screen

The capacitive touch display can be simply regarded as a screen composed of four layers of composite screens: the outermost layer is a glass protective layer, also called a cover; then the second layer is a conductive layer, and the third layer is non-conductive. The fourth innermost layer of the glass screen is also a conductive layer.

The innermost conductive layer is the shielding layer, which plays the role of shielding the internal electrical signals. The middle conductive layer is the key part of the entire touch screen. There are direct leads on the four corners or sides to detect the position of the touch point. The uppermost covering layer is tempered glass or polyethylene terephthalate (PET). The advantage of PET is that the touch screen can be made thinner, and on the other hand, it is cheaper than the existing plastic and glass materials.

The insulating layer is glass (0.4-1mm), organic film (10-100um), adhesive, and air layer. The most important layer is the indium tin oxide layer. The typical thickness of ITO is 50-100nm, and its sheet resistance is in the range of about 100-300 ohms. The three-dimensional structure of the ITO process has a great influence on the capacitive touch screen. It is directly related to the two important touch screen pcap parameters of the touch screen: inductive capacitance (finger and upper ITO) and parasitic capacitance (upper and lower ITO, lower ITO and display screen).

Ⅱ. The working principle of capacitive touch screen

When a finger touches the metal layer of a capacitive touch panel, because of the human body electric field, the user and the touch screen surface form a coupling capacitor. For high-frequency current, the capacitor is a direct conductor, so the finger sucks one from the contact point. Very small current. This current flows from the electrodes on the four corners of the touch screen, and the current flowing through these four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position of the contact point after accurate calculation of the four current shares. .

After the capacitive touch screen receives the touch signal, it 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 through analog-to-digital conversion and demodulation, and finally sent to a DSP for data processing.

Ⅲ. The categories of capacitive touch screen

1. According to the number of touch points, it can be divided into single-point touch and multi-point touch;

2. According to the sensing method, it can be divided into surface touch screen and projected capacitive touch screen;

3. According to the different material structure, it can be divided into single-layer ITO, single-sided double-layer ITO, and double-sided single-layer ITO.