Sectional structure of TFT-LCD

Sectional structure of TFT-LCD

The Chinese translation name of TFT LCD is called Thin Film Transistor Liquid Crystal Display. We mentioned from the beginning that liquid crystal displays need voltage control to generate grayscale. And the display that uses thin film transistors to generate voltage to control the rotation of liquid crystals is called TFT LCD. From the cross-sectional structure diagram, the liquid crystal is sandwiched between the upper and lower glass layers to form a parallel plate capacitor, which we call CLC (capacitor of liquid crystal). Its size is about 0.1pF, However, in practical applications, this capacitor cannot hold the voltage until the next time the screen data is updated. That is to say, when the TFT charges the capacitor, it cannot hold the voltage until the next time the TFT does it again. When charging. (At the general 60Hz screen update frequency, it needs to maintain about 16ms.) In this way, if the voltage changes, the displayed gray scale will be incorrect. Therefore, generally in the panel design, it will Add a storage capacitor CS (storage capacitor about 0.5pF), so that the charged voltage can be maintained until the next time the screen is updated. But to be correct, the TFT itself growing on the glass is just a transistor The switch made. Its main job is to determine whether the voltage on the LCD source driver should be charged to this point. As for how high voltage should be charged to this point, in order to display what kind of gray scale. It is all from the outside LCD The source driver decides.

Color filter:

We divide the three colors of RGB into three independent points, each with different grayscale changes, and then regard the three adjacent RGB display points as a basic unit of display, that is, pixel. Then this pixel, You can have different color changes. Then for a display screen that requires a resolution of 1024*768, we only need to make the composition of the flat-panel display 1024*768 pixels, and then this screen can be displayed correctly.

Aperture ratio: A very important parameter in crystal displays is brightness, and the most important factor that determines brightness is the aperture ratio. The aperture ratio is the ratio of the effective area through which light can pass. When the light is emitted from the backlight board, not all the light can pass through the panel, such as the signal traces for the LCD driver chip, the TFT itself, and the storage capacitor. These places are not completely transparent. Because the light passing through these places is not controlled by the voltage, and cannot display the correct gray scale, it needs to be shielded so as not to interfere with the correct brightness of other light-transmitting areas.