Yuhua micro: basic structure principle of capaciti
2021-06-03 16:59:33
The basic structure of the capacitive touch screen is: the substrate is a single-layer plexiglass, a layer of transparent conductive film is uniformly forged on the inner and outer surfaces of the plexiglass, and a long and narrow electrode is tapered on the four corners of the transparent conductive film on the outer surface. Its working principle is: when the finger touches the capacitive touch screen, the high-frequency signal is connected on the working surface. At this time, the finger forms a coupling capacitance with the working surface of the touch screen, which is equivalent to a conductor. Because there is a high-frequency signal on the working surface, when the finger touches, it sucks a small current at the touch point, which flows out from the electrodes at the four corners of the touch screen respectively, The current flowing through the four electrodes is proportional to the linear distance from the finger to the four corners. The controller can obtain the coordinate value of the contact point through the calculation of the proportion of the four currents.
The outer layer of the touch screen can be regarded as the conductive glass layer, and the fourth layer is the conductive glass layer, which can be regarded as the protective layer behind the touch screen. The inner conductive layer is the shielding layer, which plays the role of shielding the internal electrical signal. The middle conductive layer is the key part of the whole touch screen. There are direct leads on the four corners or four sides, which are responsible for the detection of the position of the touch point.
The upper covering layer is toughened glass or polyethylene terephthalate (PET). The advantage of pet is that the touch screen can be thinner. 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. One of the important layers is indium tin oxide (ITO) layer. The typical thickness of ITO is 50 ~ 100nm, and its block resistance is about 100 ~ 300 ohms. The three-dimensional structure of ITO technology has a great impact on the capacitive touch screen. It is directly related to two important capacitance parameters of the touch screen: inductive capacitance (between finger and upper ITO) and parasitic capacitance (between upper and lower ITO and between lower ITO and display screen).
The structure of capacitive touch screen is mainly to coat a transparent film layer on the glass screen, and then add a protective glass on the conductor layer. The double glass design can completely protect the conductor layer and sensor. At the same time, it has higher light transmittance and better support multi touch.
The capacitive touch screen is plated with long and narrow electrodes on the four sides of the touch screen to form a low-voltage AC electric field in the conductor. When touching the screen, due to the human electric field, a coupling capacitor will be formed between the finger and the conductor layer, and the current from the four electrodes will flow to the contact, and the current intensity is inversely proportional to the distance from the finger to the electrode. The controller behind the touch screen will calculate the proportion and intensity of the current and accurately calculate the position of the touch point. The double glass of the capacitive touch screen can not only protect the conductor and sensor, but also effectively prevent the impact of external environmental factors on the touch screen. If the screen is stained with dirt, dust or oil, the capacitive touch screen can still accurately calculate the touch position.
Because the capacitance changes with the contact area and the dielectric of the medium, its stability is poor and often drift occurs. This kind of touch screen is suitable for the debugging stage of system development.
Principle of capacitive touch screen
Capacitive touch screen technology works by using the current induction of human body. The capacitive touch screen is a four layer composite glass screen. The inner surface and interlayer of the glass screen are coated with a layer of ITO, the outer layer is a thin layer of silica glass protective layer, the interlayer ITO coating is used as the working surface, four electrodes are led out from the four corners, and the inner ITO is the shielding layer to ensure a good working environment. When the finger touches the metal layer, a coupling capacitance is formed between the user and the touch screen surface due to the human electric field. For high-frequency current, the capacitance is a direct conductor, so the finger sucks a small current from the contact point. The current flows out from the electrodes on the four corners of the touch screen, and the current flowing through the four electrodes is directly proportional to the distance from the finger to the four corners. The controller obtains the position of the touch point through the accurate calculation of the proportion of the four currents.
Shenzhen Yuhua Micro Technology Co., Ltd. is a company engaged in the development and sales integration of LCD and LCM. It is located in Longhua new area, Shenzhen. It has superior geographical location, beautiful environment and convenient transportation. In addition, the company has gathered backbone talents with rich experience and operation ability in marketing, product R & D, product production, project implementation, customer service and technical training, and has strong management and technical ability.
