Basic knowledge of TFT-LCD

Color filter (CF)

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 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, then this screen can be displayed correctly. The black part between each RGB point is called the Black matrix. The black matrix is mainly used to cover the part that is not intended to transmit light. For example, some ITO traces, or Cr/Al traces, or TFT parts. Each RGB highlight does not look like a rectangle. There is also a part that is covered by the black matrix in the upper left corner. This black missing corner is where the TFT is located.

Back light (BL)

In a general CRT screen, a high-speed electron gun is used to emit electrons to hit the phosphors on the silver light screen to generate bright light to display the picture. However, the liquid crystal display itself can only control the brightness of light passing through, and has no light-emitting function. Therefore, a backlight must be added to the LCD to provide a light source with high brightness and uniform brightness distribution. The main parts that make up the backlight plate are lamp tubes (cold cathode tubes), reflector plates, light guide plates, prism sheets, diffuser plates and so on. The lamp tube is the main light-emitting part, and the light is distributed everywhere by the light guide plate. The reflective plate restricts the light to the direction of the TFT LCD. Finally, with the help of the prism sheet and the diffuser, the light is evenly distributed to each area to provide a bright light source for the TFT LCD. The TFT LCD controls the rotation of the liquid crystal by voltage and controls the brightness of the passing light to form different gray levels.

Aperture ratio

One of the most important specifications in liquid crystal displays is brightness, and the most important factor determining brightness is the aperture ratio. When light is emitted through the backlight, not all light can pass through the panel, such as the signal traces for the LCD source driver chip and gate driver chip, the TFT itself, and the storage capacitor for storing voltage. Wait. In addition to the incomplete light transmission in these areas, the light passing through these areas is not controlled by the voltage and cannot display the correct grayscale, so black matrix must be used to shield them so as not to interfere with the correct brightness of other light transmission areas. .