Analysis of three types of LCD wide viewing angle technology

After experiencing rapid development in 2005, LCD technology has entered a new field. Response time, contrast, brightness, viewing angle... have all reached a new level, but there is also an obvious problem in front of us, that is, in the face of many high-parameter LCD products, how can we judge the performance of LCD monitors?

　　Undoubtedly, "wide viewing angle technology" is the most direct judgment method, because wide viewing angle technology is one of the new generation technologies promoted by major LCD manufacturers. It is not only related to the viewing angle of the LCD display, but also directly affects the response time, brightness and other performance parameters of the LCD display. At present, there are four main types of wide viewing angle technologies used by major LCD brands: TN + Film (TN + viewing angle expansion film) wide viewing angle technology, Fujitsu's MVA technology, Hitachi's IPS technology, Samsung's PVA technology, etc. Although these technologies are mainly based on improving the viewing angle, shortening the response time, color performance, and improving contrast are also included in these technologies.

　　Before we learn about these wide-viewing angle technologies in detail, we must first understand the definition of viewing angle for LCDs. LCDs are different from CRTs. Due to their inherent physical properties, when users look at them from different angles, the displayed images will be distorted. We call the critical angle at which the image quality changes to an unacceptable level its viewing angle. Image distortion mainly includes contrast, color difference, and grayscale inversion (low grayscale is brighter than high grayscale).

　　TN＋Film (viewing angle expansion film) wide viewing angle technology

　　TN+Film wide viewing angle technology is the most widely used technology in the low-end LCD market. It is based on the traditional TN mode LCD, but adds a film process to the original LCD panel. Since there are not many technological updates, the original production line is still used, which will not lead to a decrease in the yield rate of LCD products, and the cost is also controlled, so the price is lower, which is also an important reason why it can sell well in the low-end market.

　　So why can this technology only be applied to low-end LCDs? First of all, the problem of bright spots has not been improved in this technology. In addition, the long response time, few color elements, and low aperture ratio of TN mode LCDs have not been improved in this technology. Therefore, this technology only improves the viewing angle, and it is obvious that it cannot be adopted by the high-end LCD market. Its low cost and less than ideal performance determine that it can only be in the low-end market.

　　Although TN+Film (viewing angle expansion film) wide viewing angle technology has many shortcomings, it is not a very backward technology. Due to its mature technology, it only needs to adopt more precise driving and optimization technologies to overcome some of its inherent shortcomings. For example, the response time and maximum color reproduction number are superior to other new wide viewing angle technologies. Of course, the cost of optimized TN+Film LCD monitors is also relatively increased, so the selling price must be slightly higher.

　　At present, most LCD manufacturers have TN mode LCD products, which can obtain a wider viewing angle by simply attaching a viewing angle expansion film. However, it is worth noting that although low-end TN mode LCD products have extremely wide viewing angles, they are prone to bright spots. The way to determine whether it is TN mode is to stand on the side of the monitor and observe the color changes of the LCD. If the bright areas of the picture look darker from the side, and the dark areas become brighter, it means that it is a TN panel.

IPS wide viewing angle technology

　　IPS wide viewing angle technology is also called plane control mode wide viewing angle technology. As the name implies, this technology mainly improves the viewing angle by switching the plane of liquid crystal molecules. It makes full use of the changes in spatial thickness, friction intensity, and lateral electric field drive to make the liquid crystal molecules rotate at a large angle. This technology allows users to only see the short axis of the liquid crystal molecules under any circumstances, so that the screen can be viewed from all angles with less impact on the visible range of the picture. IPS wide viewing angle technology is more perfect than the previous two technologies. The viewing angle of LCD monitors using IPS technology can reach 170 degrees, which can be said to achieve a truly ultra-wide viewing angle.

　　However, this technology also has some disadvantages. Because the liquid crystal molecules must switch horizontally, the electrodes must be made into a comb shape and then placed on the glass substrate below. The direct consequence of this is a reduction in contrast. Therefore, this technology has little effect on improving contrast and brightness. At present, IPS technology has developed three generations. The first generation of IPS technology achieves a good viewing angle. The second generation S-IPS technology introduces a dual-domain mode, which is a great improvement over the first generation. The third generation AS-IPS technology increases the aperture ratio, which improves the inherent low brightness defect and significantly improves the brightness.

　　Because IPS technology is not like other modes that only perform well in four angles, it has very good viewing angles in all directions. Because of its excellent performance, IPS technology is currently supported by high-end LCDs from first-tier manufacturers such as LG and Philips. This technology is a relatively perfect wide-viewing angle solution, and basically the picture will not be distorted with the viewing angle. Although its ability to restore black is slightly inferior to MVA technology, it can use optical film to make up for this deficiency.

　　The method of judging IPS mode is also very simple. Since the long axis of the liquid crystal molecules is parallel to the screen, it is not greatly affected by external forces. If you gently press the screen with your fingers, other modes of LCD monitors will have obvious distortion ripples, while IPS mode LCD monitors will have much less distortion.

　　PVA wide viewing angle technology

　　PVA is a wide-viewing angle technology promoted by Samsung that is very similar to MVA. It can also be said to be a variation of MVA. The only difference is that PVA uses a transparent ITO layer to replace the protrusions in MVA. This manufacturing process can use transparent electrodes to obtain a better aperture ratio, minimize the waste of backlight, and thus improve image quality. PVA is also a normally dark mode liquid crystal. When the TFT is damaged and cannot receive electricity, the pixel is dark. This greatly reduces the possibility of bright spots appearing on the LCD panel.

　　Since this technology directly changes the structure of the liquid crystal unit, the performance is greatly improved. The viewing angle reaches 170 degrees, the response time is controlled within 25 milliseconds, and it has an ultra-high contrast ratio of 500:1 and a primary color display capability of up to 70%.

　　In addition to the above wide-viewing angle technologies, there is also the CPA wide-viewing angle technology launched by Sharp, the OCB wide-viewing angle technology launched by Panasonic with wide viewing angle and high response speed, the ExtraView technology used by NEC for its own LCD, and the FFS technology promoted by BOE-Hydis. What deserves attention is the FFS technology, which has almost improved all the defects of IPS technology. Currently, almost all LCD products on the market use FFS technology as long as the viewing angle is marked as 180 degrees or 178 degrees. Therefore, in the next few years, in addition to the above-mentioned mainstream wide-viewing angle technologies, FFS technology is very likely to become the mainstream technology of LCD.