Since the advent of the TFT screen car navigation system in the 1990s, after 20 years of development, it has become a digital electronic machine that can be seen everywhere in life. More than 70% of new cars in Japan are equipped with navigation devices. This article refers to the address: http:// According to the survey, most Japanese people hope to see TV in the car, especially the hard disk navigator that supports terrestrial digital TV, digital music and other functions, has become the main factor driving the purchase of navigation devices. Less than 10% of cars equipped with car navigation systems in Europe are different from Japanese cars with various entertainment features in the navigator. The European-made car uses the Human Machine InteRFace/Man Machine Interface (HMI/MMI). As a driving support interface, there are many models equipped with LCD monitors centered on premium cars. The situation in the United States is different. Because the road planning in the United States is very systematic, as long as the destination can be reached according to the street name and number, the demand for car navigation systems is not familiar, but the whole parent is away from the trip. In the back seat, the use of liquid crystal displays to watch DVDs and TV entertainment is very popular for instant entertainment. Vehicle LCD monitors with path navigation, driving support, and game entertainment development are undergoing major application changes along with the popularization of car navigation systems under the harsh environment of automobiles. Recently, even through car navigation systems, they have become cars. Meter warning and driving aid display. The reliability and quality requirements of automobile manufacturers are severe. It is not comparable to the consumer industries such as general household appliances, computers, and digital products. It involves the development of high-reliability liquid crystal displays, quality management systems, and daily production activities. Operating system. Required characteristics Environmental resistance The most basic required characteristic of automotive liquid crystal displays is environmental resistance. Table 1 is the reliability test specification for automotive liquid crystal displays. Because of the different auto manufacturers, it requires more stringent environmental resistance tests, such as high temperature +95 ° C, low temperature -40 ° C, high temperature and high humidity 65 ° C, humidity 90%, test time 2000 hours, etc. Randomly sampled samples were tested to confirm the characteristics that are practically in full compliance with environmental testing requirements. The above is a test item on reliability. In fact, liquid crystal displays are also used in such a temperature range. Therefore, various electrical, mechanical, and optical characteristics are required to operate normally in such a temperature range, but all characteristics are in such a temperature range. The results of the balance are not easy to be obtained, including the optical characteristics at low temperatures, the self-heating at high temperatures, and the limit of reliability. The current performance cannot fully meet the requirements of automobile manufacturers. Table 1 Reliability test specifications for automotive liquid crystal displays The characteristics of the LCD monitors that are completely different from other uses are the first to emphasize the brightness of the screen. The main reason is that the LCD monitor for vehicles uses strong sunlight in the outdoor environment and requires high visibility of the image. Generally, the mobile phone can be indoors or outdoors. Under the use, the mobile phone can change direction or use the hands and body to cover the sunlight. However, the liquid crystal display fixed in the car cannot change direction arbitrarily, so the brightness of the screen must be exceeded. A touch panel similar to a car navigation device is pasted on the screen, and the touch panel causes a decrease in the transmittance. In addition, the surface of the touch panel reflects external light, resulting in a decrease in visibility of the liquid crystal display. Although Sharp Corporation of Japan has made touch sensors around thin film transistors, it is trying to improve the light transmittance and reflection of touch panels, but this will make the production process and cost more complicated and expensive. The brightness of automotive LCD monitors is usually very high. Some LCD monitors have built-in (In-panel) penetrating acrylic panels with a penetration rate of less than 50%. Advanced models also have an overall design. When the engine is not activated, the LCD monitor screen It is completely black, and in this case, a high-brightness liquid crystal display is particularly required. Generally, the liquid crystal display has a brightness of 450 to 500 cd/m2 as a standard value, and in some cases, a specification of 450 to 500 cd/m2 or more, or even more than 1000 cd/m2 or more, the main reason is that the transmittance of the liquid crystal display has a certain limit. Therefore, it is necessary to greatly increase the brightness of the backlight module. Another difference between automotive LCD monitors and mobile phones, NB and PC is the angularity of the brightness, because the light distribution characteristics of automotive LCDs are very special. Mobile phones, NBs, PCs, and other personal electronic products mostly use the display as a front-end. As long as the front brightness is maintained as a product, there is no problem. However, in the case of a car, the liquid crystal display is mostly fixed on the side of the instrument panel, from the driver and the driver. The assistant's seat is viewed at an angle of about 30 degrees, so the light distribution characteristics of the car and the mobile phone are quite different, but these characteristics can be obtained by the optical film combination of the components of the backlight module. Fig. 1 is a light distribution characteristic of a liquid crystal display for a mobile phone and a mobile phone. (1) and (2) are examples of light distribution characteristics of a crystal display for a vehicle, and (4) are light distribution characteristics of a liquid crystal display for a mobile phone. Example. The liquid crystal display of a mobile phone itself has a very low brightness, but it uses an optical diaphragm to converge light in the front direction, even if the front side of the same light source can change very brightly. (3) A light source structure of a vehicle liquid crystal display constructed by using the same optical film as a mobile phone. It can be seen that when the optical film structure is the same as that of the mobile phone, even if the light source is the same as that of the general vehicle, the front brightness is about 1.4 times, but the brightness of the 30 degree angle is reduced by 40%. In summary of the above phenomenon, if the liquid crystal display for a vehicle is compared with a mobile phone, even if the same screen area, the brightness required by the light source needs to be: The ratio of front luminance is approximately 2 times × the ratio of light distribution characteristics is approximately 1.4 times = 2.8 times Here, for example, a liquid crystal display for a 7-inch vehicle and a liquid crystal display for a 2.75-inch mobile phone, the above-mentioned 2.8 times need to multiply the area ratio of the display range of the two screens by about 8.6 times, and then simply calculate the light source of the liquid crystal display for the vehicle. It takes about 24 times. In other words, the power consumption, heat and cost of the backlight module for the car are much larger than those of the portable product. The light distribution characteristics described above are characteristics at normal temperature and in a stable state. The light source of the backlight module of the vehicle liquid crystal display mainly uses a cold cathode lamp (CCFL). When the temperature is low, especially after lighting, the brightness is increased by a few minutes to a few degrees. For example, the brightness at the beginning of the -20 °C lighting is 10~ of the normal temperature. About 20%, as shown in Figure 2, the liquid crystal display of the cold cathode lamp type, low brightness has been regarded as a major issue. Figure 2 Comparison of luminance-angle characteristics of CCFL and LED backlight modules Up to now, LCD panel manufacturers have made various countermeasures for backlight modules, such as reducing the gas pressure of cold cathode lamps, current regulators (Boost), etc., but it is generally believed that the fundamental solution is LED lighting of backlight modules. In fact, the light source of the backlight module of the mobile phone uses LED from the beginning, but the backlight module of the car has not used the LED light source for a long time. The main reasons are as follows: ·According to the combination of brightness, light distribution characteristics and picture size, the energy required for automotive liquid crystal displays is very large. In addition, the luminous efficiency of LEDs is very low, so the power consumption of LEDs is always higher than that of cold cathode lamps. ·In order to ensure reliability under the temperature conditions of the vehicle, the maximum allowable current and temperature of each LED must be greatly reduced, that is, the maximum current value applied at high temperature must be 60% to 71% of the normal temperature, and the portion with reduced brightness Then increase the number of LEDs used to maintain brightness; • As a result of the deterioration cycle, the cost of the LED backlight module is increasing. In recent years, the luminous efficiency of LEDs has been greatly improved. In 2005, the power consumption of LEDs finally reached the same level as that of cold cathode lamps, and it was used as a light source for backlighting modules for vehicles. In the LED lighting of the backlight module, the problem of brightness characteristics at low temperatures is first removed, and mercury, which is an environmentally-friendly material, is completely eliminated. In particular, major automobile companies around the world have always regarded the integration and participation of environmental protection as an important issue. Based on the cost limitation of LED backlight module, car navigation and low-cost models have not been popularized yet. However, with the improvement of LED luminous efficiency and high reliability, the backlight module will be fully LEDized in the future. reaction speed Recently, the response speed of large-scale LCD TVs has often become the focus of the topic. The main reason is that large LCD TVs are prone to image quality for fast-moving images such as sports, but this problem is simply a phenomenon at room temperature. The liquid crystal display for vehicles is arguing for a reaction speed of -20 ° C and -30 ° C. As shown in FIG. 3 , the viscosity of the liquid crystal increases at a low temperature, and the reaction speed is drastically lowered. In addition, the LCD screen of the car is smaller than the LCD TV, and does not require high-quality LCD TVs, so it cannot be the object of discussion at room temperature. Figure 3 reflects the temperature dependence of speed When the reaction speed at low temperature is less than 150ms, for example, when the car suddenly runs over the bicycle in the movie, the scene cannot be clearly recognized. In some cases, the driving information such as the pointer displayed on the liquid crystal display may be blurred, and the dangerous situation may not be recognized. In order to solve the above problems, it is required that the temperature characteristic range of the liquid crystal material is very wide, and the liquid crystal material for a vehicle uses a material having a solidification temperature of -40 ° C or lower. However, when the liquid crystal approaches the solidification temperature, the viscosity sharply increases, so that the liquid crystal material must have a low viscosity, and at the same time The gap between the two glass substrates next to the liquid crystal material is narrowed, because the narrow liquid crystal gap greatly contributes to the reaction speed of the liquid crystal, but the production of the liquid crystal display by the narrow liquid crystal gap control method has a certain influence on the yield. The reaction speed of liquid crystal displays varies greatly with the liquid crystal display mode. In the past, liquid crystal displays for vehicles used TN liquid crystals as the mainstream. The low-temperature reaction speed of TN liquid crystals was very good, and it was easy to achieve low cost. The quality of ASV (Advanced Super View) liquid crystal, the reaction speed between black and white is comparable to that of TN liquid crystal, but the reaction speed of intermediate color gradation such as black and gray is very slow, and the countermeasures such as adding an overshoot drive circuit can overcome The difference between the color levels is shown in Figure 4. Figure 4 The principle of the action of the Overshoot driver IPS (In Plane Switching) liquid crystal used in other high-definition panels of liquid crystal display manufacturers, there is no intermediate color gradation delay similar to ASV liquid crystal, and there is no significant difference in any color gradation, but the liquid crystal is not high-speed reaction at low temperature. It is generally believed that the IPS liquid crystal is bound to adopt the ASV liquid crystal plus overdrive technology to effectively improve the reaction speed of the liquid crystal display. Development trend of automotive LCD High image quality Car navigation has become popular and has gradually become a daily commodity. In addition to maintaining the original characteristics, the popular model has become the highest order. The advanced models continue to develop in high image quality. The main reason is that the home LCD TVs continue to evolve with high image quality, resulting in high-end car owners also hoping to pursue high-quality car displays. The second is high-quality. The fundamental method is to improve the contrast of the image to make the black picture blacker. Even if the black picture is displayed at night, the light of the backlight module will not leak light, and it can be fully integrated into the surrounding environment and design, as shown in Figure 5. The so-called contrast characteristic is calculated as a percentage of "white brightness" / "black brightness". In other words, the value of the infinite system comparison becomes larger, so that the image displayed in black can be made infinitely close to black. In the past, LCD monitors in the world published 2500:1 of the world's highest contrast LCD LCD monitors. In addition to using ASV liquid crystals, the company also significantly suppressed light leakage in color filter diaphragms and polarizing diaphragms. The reason for the light scattering phenomenon is to achieve such a high image contrast value. These high-quality images are usually related to the panel transmittance. For example, high image quality will reduce the transmittance of the panel. If the brightness of the same panel is maintained, it is necessary to increase the brightness of the backlight module. It will cause a series of problems such as increased heat generation, increased system thickness and edge width, and increased cost. The cold cathode lamp backlight module has its limit for achieving high brightness in the same shape. In comparison, there is still a lot of room for improvement of the luminous efficiency of the LED backlight module. Therefore, LCD manufacturers generally believe that the future development of the LED backlight module is very good. It is worth looking forward to. Large-scale trend Most of the contents mentioned above are concentrated on the liquid crystal display of car navigation. In recent years, car manufacturers have proposed to replace the traditional mechanical driving information pointer instrument with liquid crystal display. In the past, some models used LCD, vacuum fluorescent tubes and other components as digital driving information display. The main features of these displays are fixed regardless of color and display content, and they are all single functions. At present, the car manufacturer's proposal is to replace it with full color. The high-definition liquid crystal display can be used to switch display contents at any time according to actual needs, and provide various information necessary for the driver. The specific method described above is to embed an 8-inch TFT liquid crystal display in the instrument panel to display the same image as a conventional mechanical finger meter. If you switch to an infrared camera at night, you can also identify animals and pedestrians in dark places. It can be switched to night image mode, LCD panel with multi-function in-panel (In-Panel), which has been adopted by some auto manufacturers in 2005. The display screen of various embedded LCD panels will appear in the future, as shown in Figure 6. The display includes engine speed, speed, water/oil and other driving information and navigators, various warning displays, vehicle status, or electronic rear-view mirrors using front and rear cameras, or wireless networks. Information such as information, TV, DVD, online games, movies, etc., so some manufacturers use full-color high-definition LCD monitors with a screen size of more than 12 inches. However, car manufacturers privately believe that the information provided is so complicated, especially that some information requires the driver to make an instant judgment while driving. However, as the display method is different, the driver will be more confused, so the car manufacturer thinks that the display method is necessary. Full consideration and planning. In addition, there are many regulations on freedom of regulations, so automakers have almost fallen into the dilemma of having to review more carefully, but overall, the dashboard of the future car will definitely develop toward high-definition full-color LCD monitors. Figure 7 Cross-sectional structure of a semi-transmissive liquid crystal display Liquid crystal display for vehicle liquid crystal display Semi-transparent high-definition full-color LCD display As mentioned above, the brightness of the liquid crystal display for the vehicle must exceed the ambient light, but the pixels of the semi-transparent high-definition full-color liquid crystal display have high penetration electrodes and reflective electrodes, as shown in Figure 7, the reflective electrode parts. The cell gap (Cell Gap) is only half of the penetrating electrode. The penetrating and reflecting electrodes form a multi-gap structure. By using this special structure to combine the optical characteristics of penetration and reflection, the brightness of the display can be improved. Troubled. The light transmittance of the reflective electrode portion of the semi-transparent high-definition full-color liquid crystal display is lowered, and as a result, the brightness of the backlight module is lowered, but once the external light is brightened, the external light is incident, and the electrode portion is reflected. The brightness will increase, so the semi-transmissive liquid crystal display can maintain certain picture recognition in any external light environment. Figure 8 is a comparison result of the visibility of a semi-transparent high-definition full-color liquid crystal display and a conventional transmissive liquid crystal display under the same external light, and the picture shows the brightness of the conventional transmissive liquid crystal display when the illumination becomes stronger. The slightest improvement is mainly due to the extra reflected light such as the surface of the polarizing plate, which actually helps the image. In contrast, the transflective high-definition full-color liquid crystal display has no external light, and the brightness of the screen is only a transmissive liquid crystal display. In half, under the external light of 60,000 illuminance (lx), the brightness of the picture exceeds 2500 cd/m2. Double display The driver needs to navigate the picture data, and the passengers of the assistant seat want to watch the TV more and more, and can meet the demand at the same time is the so-called dual view (Dual View) high-definition full-color liquid crystal display. Basically, such a liquid crystal display is to set a parallax barrier in a panel pixel, and then separately input different image images, and the viewer can only read the image of the liquid crystal display from the left and right single side angles, so that Meet the needs of passengers and assistants to watch LCD screens. This article describes the development skills and future developments of automotive LCDs. The car carries out an unprecedented electronic innovation campaign that instantly provides drivers with all the necessary driving information and wireless LCD transmission technology to provide passengers with TV, DVD, online games, movies and other services. Its importance and necessity are receiving more and more attention. It is generally believed that the future automotive LCD monitors will completely replace the traditional mechanical pointer instrument panel, and the combination of the liquid crystal display and other electronic sensors and cameras can provide a safe and comfortable driving environment for the driver. At the same time, automotive liquid crystal displays are bound to pursue higher visibility, which means that the development of quality and reliability enhancement technologies will become a problem that LCD display system manufacturers must overcome.
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Standing characteristics of CCFL and LED brightness 
High-definition factors other than high contrast, the widening of the range of color is also very important, especially for automotive LCD monitors, most of which are placed in the center console between the driver and the assistant's seat, viewing the screen from about 30 degrees left and right. . In addition, considering the movement of the front and rear of the seat, the design is mostly designed to lock the picture quality (or contrast) at 45 degrees left and right. Therefore, the high contrast and the expansion of the visual range are also important factors for high image quality. one.
The expansion of the color reproduction range is also very important. The home LCD TV is constantly pursuing the NTSC ratio and the color reproduction range in pursuit of high-definition and vivid image images. In fact, the liquid crystal display for vehicles also has the same development trend, such as the automotive liquid crystal used in advanced cars. The display has evolved from the NTSC ratio of about 50% in the past to 65% and 75%. It is generally believed that the NTSC ratio will continue to increase in the future. 
Conclusion
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