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Mobile Phone LCD Screen Quality Control Expert

TFT-LCD liquid crystal display and working principle

by:Kimeery     2023-03-16
Now that this society is flooded with colorful LCD displays, how much do you know about the working principle of TFT-LCD liquid crystal displays? Let's take a look at the working principle of the TFT-LCD liquid crystal screen. TFT-mobile phone LCD LCD screenprinciple: The principle of LCD screenis based on the characteristic that the light transmittance of liquid crystal changes with the magnitude of the applied voltage. When the light passes through the upper polarizer, it becomes linearly polarized light, and the polarization direction is consistent with the vibration direction of the polarizer, and is consistent with the arrangement order of the liquid crystal molecules on the upper and lower glass substrates. When light passes through the liquid crystal layer, the linearly polarized light is split into two beams due to refraction by the mobile LCD screen. And because the propagation speed of the two beams of light is different (the phase is the same), when the two beams of light are combined, the vibration direction of the vibrating light will inevitably change. The light passing through the liquid crystal layer is gradually distorted. When the light reaches the lower polarizer, the vibration direction of its optical axis is distorted by 90 degrees, and remains consistent with the vibration direction of the lower polarizer. In this way, the light passes through the lower polarizer to form a bright field. After the voltage is applied, the mobile LCD screen is oriented under the action of the electric field, and the twist disappears. At this time, the linearly polarized light passing through the upper polarizer no longer rotates in the liquid crystal layer, and cannot pass through the lower polarizer to form a dark field. It can be seen that the liquid crystal itself does not emit light, and can only be displayed under the modulation of an external light source. During the entire display process, the liquid crystal acts as a voltage-controlled light valve. The working principle of TFT-LCD can be briefly described as: when the gate forward voltage is greater than the applied voltage, the drain-source electrode is turned on, and when the gate forward voltage is equal to 0 or negative voltage, the drain-source electrode is disconnected. The drain electrode is connected to the ITO pixel electrode, the source electrode is connected to the source line (column electrode), and the gate is connected to the gate line (row electrode). displays require voltage control to produce gray scales. TFT is a display that uses thin film transistors to generate voltage to control the turning of liquid crystals. The liquid crystal is sandwiched between the upper and lower layers of glass to form a parallel plate capacitor with a size of about 0.1pF. However, in practice, this capacitor cannot maintain the voltage until the next update of the screen data, that is to say, when When the TFT fully charges this capacitor, it cannot maintain the voltage until the next time the TFT charges this point again (with a general 60Hz screen update frequency, it needs to be maintained for about 16ms). Therefore, in the panel design, a storage capacitor CS (storage capacitor is about 0.5pF) will be added in order to keep the charged voltage until the next screen update. But to be correct, the TFT itself that grows on the glass is just a switch made of transistors. Its main job is to determine whether the voltage on the LCD source driver should be charged to this point. As for how high the voltage should be charged to this point, so as to display the gray scale, it is determined by the external LCD source driver of. LCD screen mobile phone LCD screen LCD for Samsung display manufacturers'>OLED display manufacturers

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