Principle of TFT LCD

Principle of TFT LCD

In fact, the working principle of the new TFT liquid crystal display is also based on the principle of TN liquid crystal display. The structure of the two is also basically the same. The same design of filling liquid crystal molecules between the two interlayers is adopted, except that the electrode of the upper interlayer of TN is changed to a FET transistor, and the lower layer is changed to a common electrode. But there are still some differences in the working principles of the two. In terms of light source design, the TFT display adopts the "back-through" illumination method, that is, the imaginary light source path is not from top to bottom like TN liquid crystal, but from bottom to top. This approach is to install a fluorescent lamp on the back of the liquid crystal. Light pipe.

When the light source is irradiated, it first penetrates upward through the lower polarizer. It also uses the principle of liquid crystal to transmit light. Because the upper and lower interlayer electrodes are changed to FET electrodes and common electrodes. When the FET electrode is turned on, the behavior of the liquid crystal molecules will change like the arrangement state of TN liquid crystal, and the purpose of display is achieved by shielding and transmitting light. But the difference is that because the FET transistor has a capacitance effect and can maintain a potential state, the liquid crystal molecules that have previously transmitted light will remain in this state until the FET electrode is re-energized next time to change its arrangement. Relatively speaking, TN does not have this characteristic. Once the liquid crystal molecules are not pressed, they immediately return to the original state. This is the biggest difference between TFT liquid crystal and TN liquid crystal display, and it is also the advantage of TFT liquid crystal.

In summary, the liquid crystal display receives digital signals from the computer display card through the DVI interface. These signals are transmitted to the control circuit through the data line. The control circuit adjusts the thin film transistor and the transparent display board of the liquid crystal display to realize the light and the liquid crystal. No light characteristics. In this way, the background light source passes through the polarizer and the light filter layer to finally achieve the display effect.

Design and development of LCD control driver

For a liquid crystal display, it usually includes a plywood made of glass substrate, ITO (Indium Tin Oxide) film, alignment film, polarizing plate, etc., and there are two layers above and below. Each interlayer includes electrodes and grooves formed on the alignment film, and the upper and lower glass substrates are aligned at 90 degrees. Place liquid crystals in the upper and lower sandwich layers, and the liquid crystals will be aligned according to the groove direction. On the whole, the arrangement of liquid crystal molecules is like a spiral twisted arrangement. When the glass substrate is added to the electric field, the arrangement of the liquid crystal molecules changes and becomes an upright state. When the liquid crystal molecules stand upright, light cannot pass through, and as a result, black appears on the display. The liquid crystal display (LCD) will control the arrangement direction of the liquid crystal molecules according to the presence or absence of voltage, so that the panel can achieve the display effect.

There are various classification methods for LCD classification. Usually can be divided into segment type, dot character type, dot matrix type etc. according to its display mode. In addition to black and white displays, there are also multi-grayscale and color displays. When driving the LCD, an AC voltage needs to be applied to the segment electrode and the common electrode. If only a DC voltage is applied to the electrodes, the liquid crystal itself deteriorates. Liquid crystal driving methods include static driving, dynamic driving and other driving methods.