What is the structure of capacitive touch screens?

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The principle of the capacitive touch screen is that when the finger touches the metal layer, due to the electric field of the human body, a coupling capacitor is formed between the user and the surface of the touch screen. For high-frequency currents, the capacitor is a direct conductor, so the finger sucks a small amount from the contact point. current. Through the detection circuit to detect this small current change to feel the position of the finger.

Capacitive touch screens are divided into two types: surface capacitive touch screens and projected capacitive touch screens

surface capacitive touch screens

rectangular pattern
Touch lines for sensing capacitance changes

The surface capacitive touch screen only uses a single-layer ITO sensor. When a finger touches the surface of the screen, a certain amount of charge will be transferred to the human body. In order to restore these charge losses, charges are replenished from the four corners of the screen, and the number of charges replenished in each direction is proportional to the distance of the touch point, from which the position of the touch point can be deduced.

projected capacitive touch screens

The touch screen adopts multi-layer ITO layers to form a matrix distribution. The X-axis and Y-axis cross distribution is used as the capacitance matrix. When the finger touches the screen, the change of the capacitance at the touch position can be detected by scanning the X and Y axes. Then calculate where the finger is. Based on this architecture, projected capacitance can achieve multi-touch operation.

projected capacitive touch screens are divided into two modes: self-capacitance and mutual capacitance

self capacitor

1.Measure the capacitance of the signal line itself
2.Advantages: simple, slow
3.Disadvantages: non-true multipoint, susceptible to interference

mutual capacitor

1.Measure capacitance between two signals that intersect perpendicularly
2.Advantages: more real points, fast speed
3.Disadvantages: complex, high power consumption, high cost

Common projected mutual capacitive touch screens have four structures, namely G+F, P+G, G+G, and G+F+F structures. The detailed structure and characteristics are as follows

G+F structure capacitive touch screen

Structure: cover glass + film sensor.

Features: Use a single-layer film sensor, the sensor pattern has triangles, polygons, etc. according to different touch control IC,Since there is only one layer of sensor mutual compatibility products, it only supports single-point touch. After optimizing the touch software, it achieves a virtual two-point gesture touch effect.

G+F touch structure

G+F is the structure of glass cover and single-layer film structure touch sensor. The touch sensor uses a low-temperature ITO coating process, and the impedance of the touch circuit is relatively large.

the advantages of G+F structure capacitive touch screen

low cost of mold, high-cost performance, in capacitor TP

The product with the lowest price, the total thickness can be made thinner, the light transmission is good, the delivery time is short, and the shape of the cover glass can be replaced.

the disadvantages of G+F structure capacitive touch screen

only single-point touch, poor touch accuracy, unable to realize gesture operation and more functions.

Application of G+F structure touch screen

Touch screen with G+F structure
G+F structure

G+F+F structure capacitive touch screen

cover glass + film sensor + film sensor.

Features: This structure uses two layers of film sensors, and the sensor is generally a rhombus structure.

Supports real multi-point operation, supports complex tasks such as gesture touch and wake-up. The touch screen with GFF structure is the most widely used touch screen structure

G+F+F touch structure

G+F+F is the structure of the glass cover and two single-layer film structure touch sensors. Dual-layer touch sensors can achieve better performance and are the most widely used technology in small-sized touch screens.

the advantages of G+F+F structure capacitive touch screen

Due to the self-capacitance structure of the double-layer sensor film, the accuracy is high, the handwriting effect is good, it supports real multi-touch, and the shape of the cover glass can be changed.

the disadvantages of G+F+F structure capacitive touch screen

The light transmittance is poor due to the use of multi-layer film materials, which is 5% lower than the G/G structure. relatively high price

Application of G+F+F structure touch screen

G+F+F structure

G+G structure capacitive touch screen

Cover glass + sensor glass

Features: This structure adopts single-layer induction glass. Usually the sensor pattern is a rhombus structure. Glass is used as the substrate, which has high strength and good heat resistance, so the sensor can be fabricated on both sides of the glass substrate.

G+G touch structure

G+G is the structure of glass cover and single-layer glass substrate touch sensor. The glass substrate touch sensor adopts high-temperature ITO process, the quality of the ITO film layer is good, and the service life is longer.

the advantages of G+G structure capacitive touch screen

Self-capacitance touch structure with double-layer touch sensor, high precision, good light transmission, and good handwriting effect. Support real multi-touch, the shape of the cover glass can be changed, good reliability and long service life.

the disadvantages of G+G structure capacitive touch screen

The sensor glass is easily damaged after impact, and the development cost is relatively high. It is mostly used for medium and large products such as tablet computers and monitors.

Application of G+G structure touch screen

Touch screen with G+G structure
G+G structure

P+G structure capacitive touch screen

Plastic cover + sensor glass

Features: This structure adopts single-layer induction glass. Similar to the structure of G+G, just replace the cover glass with a plastic cover

P+G touch structure

P+G is the structure of glass cover and single-layer glass substrate touch sensor. Similar to the G+G structure.

the advantages of P+G structure capacitive touch screen

high touch precision, good light transmission, good handwriting effect. Support real multi-touch, good reliability, long service life, more customizable options such as the shape and color of the plastic cover.

the disadvantages of P+G structure capacitive touch screen

The sensor glass is easily damaged after impact, the strength of the plastic cover is low, and the development cost is relatively high.

Application of P+G structure touch screen

P+G structure touch screen
P+G structure

conclusão

If your cost requirements are not high, and your products are below 7 inches of tft display products, such as 4.3 inches WVGA TFT LCD, 5.5 inches HD TFT LCD suggest you choose G+F+F touch structure, excellent performance and relatively thin size. If your product is more than 7 inches of tft display products, such as 8 inches WXGA TFT LCD, 10.1 inches FHD TFT LCD, it is recommended to use G+G touch results, in the large size of G+G structure has stronger stability and durability. G+F products have poor touch accuracy, and their performance will be unsatisfactory unless your human-computer interaction interface is very simple and easy to touch. The main problem of P+G structure is that the wear resistance and strength of the plastic cover plate is poor, and it is only used in special service conditions. If you have demand in the touch screen and LCD display, please contact us, according to your usage scenarios and requirements we will give the optimal solution.

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