The basic structure of LCD capacitive touch screen is a single layer of plexiglass substrate, the inner and outer surfaces of the plexiglass are evenly wrought on a layer of transparent conductive film, respectively, on the outer surface of the transparent conductive film on the four corners of the cone on a narrow electrode.

Its working principle is that when the finger touches the capacitive touch screen, the working surface is connected to the high-frequency signal, at this time the finger and touch screen working surface to form a coupling capacitance, which is equivalent to a conductor.

Because there is a high-frequency signal on the working surface, finger touch in the touch point to absorb a small current, the small current from the touch screen electrodes on the four corners respectively, the current flowing through the four electrodes and fingers to the four corners of the linear distance is proportional to the controller through the calculation of the proportion of the four currents, you can get the value of the contact point coordinates.

Capacitive touch screen can be simply seen as a four-layer composite screen body, first of all, the outer layer is a protective layer of glass, followed by a conductive layer, the third layer is not conductive glass screen, the fourth layer behind is also a conductive layer, the inner conductive layer is a shielding layer, which plays a role in shielding the internal electrical signal, the middle conductive layer is the key part of the entire touch screen, four corners or four edges with direct leads, responsible for the touch point The location of the detection.

One of the upper cover layer is tempered glass or polyethylene terephthalate (PET), PET advantage is that the touch screen can be thinner, on the other hand, also cheaper than the existing plastic and glass materials, the insulating layer is glass (0.4 ~ 1mm), organic film (10 ~ 100um), adhesives, air layer, which is an important layer of indium tin oxide (ITO) layer. The typical thickness of ITO is 50 to 100nm, and its square resistance is about 100 to 300 ohm range.

ITO process three-dimensional structure of capacitive touch screen has a great impact, it is directly related to the 2 important capacitance parameters of the touch screen: inductive capacitance (finger and the upper layer of ITO) and parasitic capacitance (between the upper and lower layers of ITO, the lower layer of ITO and display screen).

LCD capacitive touch screen construction is mainly in the glass screen coated with a transparent thin film body layer, and then outside the conductor layer plus a protective glass, double glass design can thoroughly protect the conductor layer and sensor, while the light transmission rate is higher, but also better support multi-touch.

LCD capacitive touch screen on all sides of the touch screen are plated with narrow electrodes, forming a low-voltage AC electric field within the conductor, when touching the screen, due to the human electric field, the finger and the conductor layer will form a coupling capacitance between the four electrodes will send a current to the contact, and the current strength and the distance from the finger to the electrode is inversely proportional to the controller located behind the touch screen will calculate the proportion of current and strength, accurate Calculate the location of the touch point.

LCD capacitive touch screen double glass can not only protect the conductor and sensor, more effective to prevent external environmental factors on the touch screen, the screen is stained with dirt, dust or oil, LCD capacitive touch screen can still accurately calculate the touch location.

Because the capacitance varies with the contact area, the dielectric medium, so its stability is poor, often resulting in drift phenomenon, this kind of touch screen is suitable for the debugging stage of system development.

The principle of LCD capacitive touch screen

LCD capacitive touch screen technology is the use of human body current induction work, LCD capacitive touch screen is a four-layer composite glass screen, the inner surface of the glass screen and the interlayer is coated with a layer of ITO, the outer layer is a thin layer of silica glass protection layer, the interlayer ITO coating as a working surface, four corners lead to four electrodes, the inner layer of ITO for the shielding layer to ensure a good working environment.

When the finger touch on the metal layer, due to the human body electric field, the user and the touch screen surface to form a coupling capacitance, for high-frequency current, capacitance is a direct conductor, so the finger from the contact point to suck away a very small current, the current from the electrodes on the four corners of the touch screen, respectively, and flow through the four electrodes of the current and the finger to the four corners of the distance is proportional to the controller through the four current ratio of the precise calculation, the location of the touch point.