Home > News > The Working Principle Of Capacitive Screen

The Working Principle Of Capacitive Screen

Blaze Display Technology Co., Ltd. | Updated: Nov 27, 2018

In order to realize multi-touch on capacitive screen, it is necessary to add electrodes of mutual capacitance. In a simple word, it is to divide the screen into blocks and set a group of mutual capacitance modules in each area to work independently. Therefore, the capacitive screen can independently detect the touch situation of each area and simply realize multi-touch after processing. 

Capacity Touch Panel USES the current induction of human body to work. Capacitive screen is a four-layer composite glass screen. The inner surface of the glass screen and the interlayer are coated with ITO. 

The outermost layer is a protective layer of silica glass with a thickness of 0.0015mm.

When a user capacitive touch screen, the electric field due to the human body, your fingers and face form a coupling capacitance, because the working plane to have a high frequency signal, so the fingers on a very small current, respectively from the current screen in the four corners of the electrode, and theoretically through the four electrodes with the finger to the four corners of the current is proportional to the distance, the controller through the precise calculation of the four current ratio, it is concluded that location. 

Projective capacitive touch screens etch different ITO conductive circuit modules on two layers of ITO conductive glass coatings. The etched patterns on the two modules are perpendicular to each other and can be thought of as sliders with continuous changes in X and Y directions. As the X and Y architectures are on different surfaces, their intersection forms a capacitor node.

One slider can be used as the drive wire and the other as the detection wire. When a current passes through one of the wires in the drive wire, if there is a signal of a change in the capacitance outside, it will cause a change in the capacitance node on the other layer of wire. The change in capacitance can be detected by measuring the electrical circuit connected to it, and then converted to A digital signal by A/D controller, which can be processed by A computer to obtain the (X, Y) axis position, so as to achieve the positioning target.

During operation, the controller successively supplies power to the driving wire, thus forming a specific electric field between each node and the wire. Then scan the sensor line one by one to measure the capacitance change between the electrodes so as to achieve multi-point positioning. When the finger or touch medium is close, the controller can quickly detect the change of capacitance between the touch node and the wire, and then confirm the position of the touch.

One axis is driven by a set of AC signals, and the response across the touch screen is measured by electrodes on the other axis. Users call this' transversal 'sensing, or projective sensing. The sensor is plated with ITO pattern of X and Y axis. When the finger touches the touch screen surface, the capacitance under the touch point increases according to the distance of the touch point. The continuous scanning on the sensor detects the change of capacitance value, and the control chip calculates the touch point and returns it to the processor.


go top