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Mobile Phone LCD Screen Quality Control Expert

8 elements of LCD selection

by:Kimeery     2021-08-20
◆LCD Type ◆Quality Assurance ◆Technical Support ◆Brand and Price ◆Supply Chain Guarantee ◆Resolution and Size ◆Temperature and Brightness Number → TN, STN type → with backlight or not → determine the size → determine the working and storage temperature range ▲ graphics → monochrome or color (TFT true color or STN pseudo color) → determine the resolution → determine the size of the backlight → backlight type (LED, EL, CCFL)→Determine the working and storage temperature range. In terms of liquid crystal (LCD), from the selection point of view, we divide common liquid crystals into the following categories: segment (also known as 8-character), character and graphic dot matrix. Each character of the common segment LCD is composed of 8 segments, that is, 8 characters and one point. It can only display numbers and some letters. If a small amount of characters, Chinese characters and other symbols must be displayed, it generally needs to be customized from the manufacturer, and the characters to be displayed can be customized. , Chinese characters and other symbols are solidified in designated locations, such as calculators. For segment LCDs, we provide customized services. Character type liquid crystal, as the name implies, character type liquid crystal is used to display characters and numbers, and the display mode of graphics and Chinese characters is the same as that of segment type liquid crystal. Character liquid crystals generally have the following resolutions: 8×1, 16×1, 16×2, 16×4, 20×2, 20×4, 40×2, 40×4, etc., of which 8(16, 20 , 40) means the number of characters (numbers) that can be displayed in a row, and 1 (2, 4) means the number of displayed rows. Graphic dot matrix liquid crystal, we divide it into TN, STN (DSTN), TFT and so on. This classification should start from the liquid crystal material and the liquid crystal effect, please refer to the principle of liquid crystal display. Due to its limitations, TN liquid crystals are only used to produce character liquid crystal modules; while STN (DSTN) liquid crystal modules are generally small and medium-sized, both monochrome and pseudo-color; TFT liquid crystals, from small to large Yes, and almost all of them are true color display modules. In addition to TFT LCDs, generally small LCD screens have a built-in controller (the concept of the controller is equivalent to the main control chip on the display card), which directly provides MPU interface; while large and medium LCD screens, if you want to control its display, you need to add Controller. For the specific use of LCD, please refer to the display solution. Therefore, to choose the LCD screen you need, several aspects that need to be considered are described in detail as follows: 1. If only characters and numbers need to be displayed, and the content displayed on a screen does not exceed the character type The maximum limit of the liquid crystal (such as 40×4), you can choose the character-type liquid crystal, which can be directly connected to the MPU. 2. If you need to dynamically display Chinese characters and graphics, you can only choose graphic dot matrix liquid crystal. The next question to consider is whether to choose STN (DSTN) monochrome, false color or TFT true color. Under normal circumstances, if you use a single-chip microcomputer to control, due to its control ability, you can only choose within the range of monochrome below 640×480 and pseudo-color below 320×240; if you use PC, IPC or other masters with strong control capabilities The control module (such as the video input control module), as long as it has a LCD screenpart or an external display control, can have a larger choice. Monochrome, pseudo-color and true-color liquid crystals without built-in controllers are available. At the same time, the external dimensions should be considered. Please also note that the resolution of LCD is physically fixed, and full-screen display can only be displayed at its inherent resolution, which is different from CRT. 3. Backlight selection. When it comes to backlighting, liquid crystals need to be classified from another perspective, namely transmissive, reflective, and transflective liquid crystals. Because liquid crystals are passive light-emitting displays, they must have external light sources, liquid crystals To have a display, transmissive liquid crystals must be added with background light, reflective liquid crystals require strong ambient light, and transflective liquid crystals require strong ambient light or backlight. Character LCD, the one with backlight is generally LED backlight, mainly in yellow color (red and green tones). Generally it is +4.2V drive. Monochromatic STN small and medium dot matrix liquid crystal, mostly use LED or EL backlight, EL backlight is usually yellow-green (red, green, white tones). Generally use 400-800Hz, 70-100V AC drive, common drive requires about 1W of power. Medium and large dot matrix STN liquid crystals and TFT liquid crystals are mostly cold cathode backlight tubes (CCFL/CCFT), and the backlight color is white (red, green, and blue tones). Generally use 25k-100kHz, AC drive above 300V. Please refer to DC to AC, low-voltage to high-voltage inverters. 4. Temperature range. Many character LCDs and small graphic dot matrix LCDs have normal temperature type and wide temperature type, while large graphic dot matrix LCDs have wide temperature type in mainland China. It is rare in the market. Normal temperature generally refers to a working temperature of 0-50°C, and a wide temperature range of -20-70°C (individually, it can reach minus 30°C, such as LQ5AW136 TFT video interface); in addition, there are certain requirements in terms of humidity. 5. Brightness problem. The unit of brightness is cd/m2 or Nit. The brightness of most TN and STN (DSTN) liquid crystals does not exceed 100cd/m2, but the 5-6 inch pseudo-color STN screens are currently more commonly used. The brightness of the LCD is around 130cd/m2. Kyocera has a 5.7' LCD with a brightness of 200cd/m2, while the brightness of TFT liquid crystals is usually above 150cd/m2. Our company can also provide some ultra-high brightness liquid crystals with a brightness of up to 200cd/m2. 1000cd/m2, or even 1600cd/m2. 6. In terms of accessories, since there is no international standard for LCD specifications and interfaces, the signal interfaces of different manufacturers and types of LCDs are often inconsistent. Therefore, when choosing LCDs, pay attention to purchasing related accessories (including signal connection devices, inverters, etc.)
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