1. Liquid crystal (LC, liquid crystal):

 Liquid crystal is a kind of between solid and liquid, with regular molecular arrangement of organic compounds.

Liquid crystal properties:

•  -Liquid crystals can be penetrated by light and affect the polarization of light
•  -The liquid crystal molecules are flipped to different degrees depending on the voltage applied to the ends of the liquid crystal molecules.
•  -The polarization of light through liquid crystals varies according to the angle of the liquid crystal;
•  -Liquid crystals must be driven by an alternating current, otherwise they will be polarized;

2. Polarizer

Liquid crystal molecules can change the polarization of light. When passing through a twisted liquid crystal, the light is twisted 90 degrees by the liquid crystal molecules.

Through the TFT voltage control switch to control the voltage at both ends of the liquid crystal molecules, different differential pressure has a different penetration rate, the degree of polarization is also changed accordingly, so that the liquid crystal molecules will be polarized.

 The degree of polarization also changes accordingly, so as to achieve the purpose of controlling the intensity of light.

3. LCD structure

 LCD is a liquid crystal box made of upper and lower two pieces of conductive glass, the box is filled with liquid crystals, surrounded by sealing materials – frame (generally epoxy resin) sealing, the two outer sides of the box is affixed with a polarizer, through the TFT components to control the upper and lower substrate electric field to achieve the liquid crystal molecules rotate to achieve the purpose of the display:

•  -Glass substrate: evaporation of a layer of ITO transparent conductive layer and its flat thin glass sheet
•  -Liquid crystal: the main body of the liquid crystal display
•  Polarizer: made of plastic film material, coated with a layer of optical pressure-sensitive adhesive, can be pasted on the surface of the liquid crystal box.

 4.TFT LCD display principle

 Liquid crystal molecules will rotate when driven by an electrical signal, and the rotation will affect the light transmission.

 In the liquid crystal panel on the white light illumination (known as backlight), through the electrical signal to allow liquid crystal molecules to selectively through the backlight of the polarized light.

 TFT can actively control each individual pixel, as long as the control of the display color of each pixel, you will see a variety of different colors on the LCD panel.

 LCD itself does not emit light, only light transmission, belongs to the passive light-emitting devices.

 Active light-emitting devices: LED, CRT, OLED, etc.

5.TFT basic structure

•  When the Gate line sends in a signal, Vg receives a voltage, which induces free electrons between S and D. The Data line sends in a signal, which induces free electrons between S and D;
•  The Data line feeds the signal to make S and D conductive, and the signal makes the liquid crystal move, which determines the brightness of the pixel and charges the storage capacitor at the same time;
•  When the Gate line signal scanning is completed, the Vg voltage disappears, the switch is disconnected, so that the Data line signal can not be fed; scanning line, the switch signal line to control the gate. The transistor on the control TFT is on/off. When it is on, the data can be transmitted; when it is off, the data cannot be transmitted.

 Since the storage capacitor is charged before, after the Vg voltage disappears, the storage capacitor is discharged to maintain the brightness of the pixel.

 A basic display unit pixel requires three display points, each representing the three primary RGB colors.

To a 1024 x 768 resolution TFT LCD, a total of 1024 x 768 x 3 such a combination of points.

TFT LCD display is progressive scanning, when a Gate open, this line of the source will be output to this line of the TFT at the same time for charging, this Gate closed after the next Gate open.

 6. TFT voltage and current characteristics

The voltage-current characteristics of the TFT are shown below. Different glasses have different voltage requirements for turning the TFT on (VGH) and off (VGL).

 The following figure shows the requirement of VGH VGL for Qunitron 6517, and the initial code will be set according to this requirement.

NoseDisplay 2025.07. 16 News