What are the differences between AMOLED and TFT-LCD screens?
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First, let's talk about the light-emitting principle of AMOLED and TFT-LCD. Please see the figure below: As can be seen from the figure, TFT-LCD emits light through the backlight (backlight unit), which is turned on and off through the liquid crystal control, and then different colors are displayed through different RGB color filters. AMOLED is self-luminous, and different colors are displayed through different RGB light-emitting body combinations. Due to the different light-emitting methods, TFT-LCD requires a backlight, so the overall thickness is naturally thicker than AMOLED. This is an old picture. Although TFT-LCD has reduced the overall thickness of touch screens through various technologies such as In-cell in the past two years, AMOLED is still thinner than TFT-LCD in general. However, because AMOLED is self-luminous, it is impossible to inject liquid crystal into the glass like TFT-LCD, but to inject AMOLED's light-emitting material into AMOLED through evaporation or printing. The printing method is still in the research and development stage. At present, including Samsung, it is produced in the form of evaporation. In order to improve the yield of AMOLED evaporation, Samsung uses various PenTiles to produce. Why is PenTile said to improve the yield? For example, if the FHD resolution is 1920x1080, PenTile only needs to make it 1920x720, and users can see the effect of 1920x1080. However, after all, some pixels are sacrificed. Under special patterns, there will be display distortion problems, but that is a natural picture. In artificial pictures, such distortion is generally not found. When many people promote AMOLED, they all promote that AMOLED is more power-saving than TFT-LCD, but Zhongguancun Online has done a test and concluded that by testing two different materials, AMOLED and IPS, although the calculation methods for the subdivided items are not quite the same, we can clearly see that AMOLED is the most power-saving when displaying black, followed by green, and the most power-consuming color is white. On the other hand, the long-term display of the three colors of the models using IPS screens has no substantial impact on power consumption. From this, it is not difficult to see that using a dark background or desktop can save the phone a little bit for AMOLED screens, and the effect is indeed obvious, but for IPS screens, due to the display structure and method (using backlight), using a dark background is more power-saving. It is not true. When it comes to dimming the brightness, the yellowing of AMOLED is also a problem. However, in recent years, the evolution of AMOLED technology has slightly improved this problem. As for the AMOLED market, since AMOLED is thinner, many mobile phone manufacturers still want to use AMOLED, although the price of AMOLED is relatively expensive. It's just that in the past two years, Samsung's Galaxy series has sold so well that it has reduced the supply of domestic brand mobile phone manufacturers, which has led to domestic manufacturers not daring to use it. However, in recent years, Samsung's own mobile phone growth has been slow, and its AMOLED production capacity has increased. Since last year, the price of AMOLED has been reduced, making more and more brand mobile phones using AMOLED. In addition to Samsung, LG, and Sony, domestic manufacturers have gradually begun to make AMOLED. Shanghai Hehui, Kunshan Guoxian, BOE, and Tianma have all begun to make AMOLED, which has gradually reduced the price of AMOLED. Of course, the future of AMOLED is bright, which is also the main reason why various suppliers have started to make AMOLED. AMOLED has three directions to focus on in the future: 1. Flexible display This is a major advantage of AMOLED compared to TFT-LCD. After all, it is self-luminous, unlike TFT-LCD, which has a backlight layer, so TFT-LCD cannot be made flexible. 2. Printing production Printing can make AMOLED thinner and easier to make curved screens. However, printing technology is not mature at present, and only TCL is researching this technology in China. 3. VR As virtual reality gradually rises, the number of domestic manufacturers engaged in virtual reality has also increased. However, I often hear experiencers tell me that when he puts on VR headsets from foreign manufacturers such as Oculus, Sony and Valve, the experience is very good, but when he puts on domestic VR headsets, it is okay when he is not moving, but it will make people extremely dizzy when he moves. Why is this? According to general opinion, VR headsets are nothing more than monitors worn on the head. What is motion sickness? Let me demonstrate with a few schematic diagrams. We can see that the picture on the left is what the eyes see when an object moves from left to right in the real world: as time goes by, the trajectory of the object is a line; and the picture on the right is what is displayed by any kind of display: the image of the object jumps to the next point after being displayed at each point for a period of time; it is not a continuous movement. But once the head moves, the human eye will also move relative to the displayed object, and the trajectory of the object in the human eye will change: When the head turns left in the right picture, the trajectory of the originally stationary object becomes like the right picture, no longer a point, but jumps back to where it "should" be at the end of each frame. However, the visual persistence of the human eye will retain the image of the previous frame and this frame, so the image will cause smearing, which will cause dizziness. At this time, there are two ways to avoid dizziness: 1. If we still assume a refresh rate of 60hz and a head rotation speed of 120 degrees/second, then the head rotation within a frame is 2 degrees. With the resolution of DK2, the delay within a frame is 19 pixels. At this time, the image displayed by the head display will be quite blurry. The higher the resolution, the more serious this problem is. Calculated based on the theoretical limit resolution of the human eye, the delay within a frame will reach 600 pixels. From 60 to 90, to 120, to 200... maybe finally to 1000hz, then our visual system will completely be unable to distinguish between real and virtual. But obviously we can't increase the refresh rate to 1000hz now. Currently, Oculus Rift CV1 and HTC Vive use 90hz refresh rate, while Sony Project Morpheus uses 120hz refresh rate. 2. Reduce persistence. Persistence is a concept in the CRT display era. CRT displays use electron beams to excite the phosphors on the screen to emit light, so in fact, the pixels in each frame of the CRT display are only illuminated for a short period of time, and the pixels are dark for the rest of the time. The schematic diagram is as follows: You can see that the pixels in the LCD display are always emitting light in each frame, so the LCD display is called "full persistence" display. The middle picture shows that the pixels are only illuminated for half of the time; and the picture on the right shows that the screen is illuminated for only a very short time under ideal conditions, that is, "zero persistence". Due to the visual persistence effect of the human eye, if the refresh rate is high enough, you will not notice that the screen is only illuminated for a short time in each frame. However, in order to make up for the lack of brightness, the intensity of pixel light emission in each frame must be greatly improved. The significance of low afterglow display for VR headsets is that the trajectory of objects when the head moves is closer to the real trajectory of the physical world: At this time, the ghosting caused by head movement will be greatly reduced. Assuming that the head rotates at 120 degrees/second, the refresh rate of the headset is 60hz, and the screen is illuminated for 2ms in one frame, based on the DK2 resolution and viewing angle, the visual delay observed by the human eye within 2ms of head rotation is only 2 pixels, and the dizziness will go away. But we all know the basic display principle of LCD: selectively transmit light by flipping the liquid crystal. This means that it is difficult to use low afterglow display for LCD. (Basic display principle of TN-LCD) The fastest response time of liquid crystal flipping is 2-4ms, and the backlight principle also makes LCD unable to achieve full black. In contrast, traditional CRT displays are naturally low afterglow displays. To solve this problem, VR headsets must use actively luminous displays, such as OLED. Since each pixel is actively luminous, OLED screens can achieve low afterglow. Therefore, AMOLED still has a lot of development prospects. I hope that domestic AMOLED suppliers can mass-produce it soon. As a winner of Toutiao's Qingyun Plan and Baijiahao's Bai+ Plan, the 2019 Baidu Digital Author of the Year, the Baijiahao's Most Popular Author in the Technology Field, the 2019 Sogou Technology and Culture Author, and the 2021 Baijiahao Quarterly Influential Creator, he has won many awards, including the 2013 Sohu Best Industry Media Person, the 2015 China New Media Entrepreneurship Competition Beijing Third Place, the 2015 Guangmang Experience Award, the 2015 China New Media Entrepreneurship Competition Finals Third Place, and the 2018 Baidu Dynamic Annual Powerful Celebrity. |
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