Working principle of tft-lcd

- Dec 18, 2019-

The principle of a liquid crystal display is based on a characteristic that the light transmittance of the liquid crystal changes with the magnitude of the voltage applied thereto. 


When the light passes through the upper polarizing plate, the linearly polarized light becomes linearly polarized, the polarization direction is consistent with the vibration direction of the polarizing plate, and the alignment order of the liquid crystal molecules on the upper and lower glass substrates is consistent. 

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When light passes through the liquid crystal layer, linearly polarized light is decomposed into two beams due to the refraction of the liquid crystal. 


Since the two light propagation velocities are different (the phase is the same), the vibration direction of the vibration light is inevitably changed when the two light beams are synthesized. The light passing through the liquid crystal layer is gradually twisted. When the light reaches the lower polarizing plate, its optical axis vibration direction is twisted by 90 degrees and is consistent with the vibration direction of the lower polarizing plate. In this way, light passes through the lower polarizer to form a bright field. After the addition of the voltage, the liquid crystal is oriented under the action of the electric field, and the distortion disappears. 


At this time, by linearly polarized light of the upper polarizing plate, the dark field cannot be formed by the lower polarizing plate when the liquid crystal layer is no longer rotated. The visible liquid crystal itself does not emit light, and under the modulation of the external light source, the liquid crystal can act as a voltage-controlled light valve in the whole display process. 


The operation principle of tft-lcd can be briefly described as follows: when the forward voltage of the gate is greater than the applied voltage, the drain electrode is turned on, and when the forward voltage of the gate is equal to 0 or the negative voltage, the drain 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 electrode is connected to the gate line (row electrode). this is the simple working principle of tft-lcd