With the rapid development of electronic communication technology, various electronic devices have been widely used in recent years. In order to meet the needs of users, electronic devices gradually become smaller, lighter, thinner and simpler, and their functions become more diversified. Touch screen has been widely used in various terminal devices for its advantages of saving space and easy communication. Terminal devices with touch screens may include mobile phones (e.g., smart phones), mobile tablets, media players, tablet computers, hand-held computers, and personal digital assistants. Five-inch touch screen is a popular device for handheld game consoles and POS machines.
Capacitive touch screens work with the body's current sensors. Capacitive touch screen is a four-layer composite glass screen, the inner surface of the glass screen and the sandwich are coated with a layer of ITO (coated conductive glass), the outermost layer is a thin layer of silicon earth glass protective layer, ITO coating as the working face, four electrodes are led out from the four corners, the inner layer of ITO as the shielding layer to ensure a good working environment. When a finger touches a metal layer, the body's electric field, the user, and the surface of the touch screen form a coupling capacitance, which is a direct conductor for high-frequency currents, and the finger sucks a small current away from the point of contact. This current flows out of the electrodes on the four corners of the touch screen, and the current flowing through these four electrodes is proportional to the distance between the finger and the four corners. The controller calculates the exact ratio of these four currents to obtain the position information of the touch point.
Compared with resistive touch screen and electromagnetic sensor board, capacitive touch screen has better performance. It is easy to use because it can be induced by light touch. Moreover, the contact between the finger and the touch screen is almost free of wear and tear, with stable performance. The service life of the finger is up to 30 years after mechanical test. In addition, the whole product is mainly composed of a PCB with only one chip of high integration, with few components, good product consistency and high yield.
The use of capacitive touch screens on the iPhone undoubtedly represents a fashion trend, which undoubtedly proves its advantages.However, capacitive touch screens, despite their flaws, also face the following challenges: the human body is part of the circuit, so the drift phenomenon is serious;It is necessary to improve the performance of capacitive induction input technology to input or control point objects on small and medium-sized flat panel displays.The performance is not stable enough when the temperature and humidity change rapidly, so frequent calibration is needed and it is not suitable for metal cabinet.The touch screen may be disabled when external inductance and magnetic sense are present.