LCD backlight display principle The biggest difference between LCD and plasma is that the LCD must rely on passive light sources, and plasma TVs are active light-emitting display devices. Currently, mainstream LCD backlight technologies on the market include LED (light emitting diode) and CCFL (cold cathode fluorescent lamp).
Cold Cathode Fluorescent Lamp (CCFL)
Traditional LCD monitors use CCFL (Cold Cathode Fluorescent Tube) backlights. There are two kinds of CCFL backlight design: “side-in†and “straight-fallâ€, but the side-entry type makes the light breakage rate higher due to the light guide design, which in turn limits the brightness of the backlight. The brightness increases when the panel size increases. The lower it is, it is only suitable for 8-inch to 15-inch TFT LCD panels, which are used by individuals such as Laptops and Desktops. However, when viewing large LCD TVs at home, the brightness of the side-entry type will be difficult to meet. Straight fall.
However, the larger the size of the LCD, the higher the proportion of the cost of the backlight module, which is referred to is the straight-type CCFL backlight module, according to statistics, is also the use of straight-type CCFL backlight module, in 15 The backlight module only accounts for 23% of the overall cost in inches, but it increases to 37% by 30 inches, and when the 57-inch resolution is estimated, the cost of the backlight module will reach 50%. Therefore, the straight-down CCFL backlight is only suitable for medium-size LCD TVs with a size of about 30 inches, and is not suitable for use in larger area designs. At the same time, the CCFL uses mercury gas discharge to generate lighting. Although the current EU RoHS regulations are acceptable as long as the “mercury†dose is below the standard, no one can guarantee that the standard may be raised to zero in the future (completely inaccurate). Use), CCFL will not be available at that time, or it must be diverted to non-mercury CCFL.
Even if the mercury-free CCFL is technically feasible, the CCFL is still a closed-tube gas-discharge type electronic lighting. The resistance of the light pipe to external forces is limited, and a large collision will cause the light pipe to break and cause lighting failure. Other solid-state electronic lighting (such as LEDs) do not have this concern. In addition, because it does not need to use light guide plate, but also less light loss problem, so does not need brightness enhancement film, especially brightness enhancement film is a minority of patented technology, expensive, straight-type can be omitted Light plates and brightness enhancement films help reduce costs.
However, the straight-down type CCFL also has its disadvantages. In order to enhance the brightness of the screen, the number of light pipes must be increased. However, the result of close arrangement of the light pipes will be unfavorable for heat dissipation. Since the distance between the left and right spaces is reduced, the heat dissipation has to be increased from the thickness level. Space, however, the increase in thickness also equals some of the advantages of LCDTV: Thinness. Incidentally, the use of CCFL tubes on large-inch LCD TVs, the length of the light tube must also increase in response to the increase in the number of inches. However, in the case of longer CCFL tubes, the intermediate positions and ends of the light tubes will be The problem of luminance MURA and color MURA is prone to occur, which in turn affects the light uniformity of the backlight. In order to maintain the light uniformity continuously, the diffusion film is used to enhance the light uniformity, but the diffusion film also brings about a loss of light transmittance. To reduce the brightness, the result of the decrease in brightness has to be reinforced by increasing the number of light pipes, but as mentioned before: adding a light pipe will make it more difficult to design heat dissipation, increase the thickness of the backlight module, or even increase the power consumption, according to Understand that the power consumption of CCFL backlight modules has accounted for 90% of the total power consumption of LCD TVs. Therefore, changing the backlight technology is currently one of the directions for changing the LCD image quality.
Light Emitting Diodes (LEDs)
Since the CCFL backlight has many side-effect concerns, the industry has also sought various new backlight implementation technologies, and LED is one of the feasible solutions, such as Sony's Qualia series television, which is the high-end large size (40 inches, 46 inches) LCDTV, its backlight part is composed of WLED, called WLED backlight technology. The development of LCD monitor for LED backlight technology has also reached a substantive stage. We can already see the relevant product display at the 2007 CES exhibition.
LED backlighting has several advantages. The first is solid-state electronic lighting. It has higher resistance to collision than CCFL, and there are no concerns about the environmental regulations of mercury gas. There is no concern about UV-UV leakage, and at the same time it exceeds the saturation of color and lifespan. CCFL, the other LED can be driven as long as the forward voltage, unlike CCFL need to exchange the positive and negative voltage, even if only the positive drive voltage, LED's demand level is also lower than the CCFL. In addition, the brightness of the LED can be adjusted only by Pulse Width Modulation (PWM), and the same method can be used to suppress the afterimage problem on the TFT LCD display. However, the brightness adjustment of the CCFL is more complicated and cannot be performed. Inhibition of afterimages must be suppressed in a different way.
Although LED backlighting has many advantages, it also has its disadvantages. The first is the luminous efficiency. In terms of the same power consumption, LEDs are not CCFLs, so the heat dissipation problem is more serious than that of CCFLs. In addition, LED is a point light source, and the CCFL line type. Compared with light sources, it is more difficult to control the light uniformity. In order to achieve the best possible light uniformity, the resulting LEDs must be carefully selected for their characteristics, and a large number of consistent (wavelength, brightness) LEDs should be used for the same backlight. Among them, this selection cost is also quite high. Fortunately, the LED's luminous efficiency is still rising, and now it has been able to reach more than 100ml/W, so that the color saturation can be better, and the backlight WLED arrangement is more relaxed, so that electricity and heat problems are relieved. After the continuous improvement of the manufacturing yield rate, the cost of selecting the LED with the same bright characteristics will also decrease.
Just changing the backlight technology may not be enough to trigger the LCD revolution, so let's go look at other LCD technology development. OLED (Organic Light Emitting Diode) is an organic light-emitting diode. OLED display technology differs from traditional LCD display methods in that it does not require a backlight, uses a very thin coating of organic material and a glass substrate, and these organic materials emit light when current passes through them. Moreover, the OLED display screen can be made lighter and thinner, have a larger viewing angle, and can significantly save power. However, its current life and price limit its bottleneck in LCD development.
OLED is another high-profile panel application technology, and the implementation of small-size panels is an early stage. According to the customer's plan, there will be more models available from 2008 to 2009, but it will still be dominated by sub-panels, and even if there is a significant increase in aircraft types and shipments, the market share will not exceed. 10%. Because OLEDs are inherently thin, the conditions of comparison, viewing angles, and power saving are superior to those of TFT-LCDs, and they have always been valued by the industry. They believe that OLEDs will replace TFT-LCDs and have invested heavily in R&D for several years. However, on the one hand, the OLED technology encounters bottlenecks, and the lifetime problem needs to be overcome. On the other hand, the TFT-LCD technology continues to advance, and now it can also provide excellent contrast and perspective, resulting in OLED demand can not be greatly improved, and the market is small and oversupply , limited to price competition; originally invested in the industry can not escape the fate of dissolution and downsizing. In the past, Taiwan Shenghua Technology invested in the establishment of Shengyuan into OLED research and development. Seeing that OLED and TFT-LCD cannot compete with each other, especially the cost difference, TFT-LCD in the specifications can easily reach a viewing angle of 170 degrees, a contrast ratio of 500:1, and brightness. Increase, you can also do thin, although the reaction rate is inferior, but it can reach the range acceptable to the human eye. Therefore, the Shengyuan Garden has also been closed down, leaving only a few R&D personnel to return to Shenghua to develop materials. In the future, if OLED lifetimes and prices can be greatly improved, there are still opportunities; at this stage, products with particular characteristics and emphasizing innovations are required; the large amount of time has not yet been seen.
The AMOLED (Active Matrix/ Organic Light Emitting Diode) active matrix organic light-emitting diode panel (AMOLED) is called the next-generation display technology. Samsung Electronics, Samsung SDI, and LG Philips all attach great importance to this new display technology. At present, Samsung Electronics Co., Ltd. and LG.Philips Philips Electronics are the main directions for developing large-size AMOLED products. Judging from the product performance of current finished products, if the cost of AMOLED can be effectively controlled, the traditional LCD panel technology will be greatly challenged.
One of AMOLED's advantages: No need for backlight AMOLED One of the advantages: More color saturation AMOLED One of the advantages: It can achieve 180 degree viewing angle of IPS or VA panel. One of the advantages of AMOLED: Effectively solve the problem of LCD panel dynamic blurring in the above Of the four OLED advantages, we are particularly concerned about the fourth product feature, because in the current market all desktop LCD monitors, can not solve the LCD screen dynamic blur problem. The blurred motion picture of the LCD screen usually refers to the phenomenon that the contour of the edge is blurred in the process of picture conversion. There are two reasons for the occurrence of the dynamic picture blur phenomenon. One is the response time of the liquid crystal and the afterglow of the phosphor, and the other is One is a TFT driver, just like the Hold mode image control.
Hold is the main cause of blurry images caused by dynamic <br> <br> so-called "Hold mode" display mode, the display is a Frame image within a certain period of time, while in the TV picture, this Hold time is equivalent to a vertical period (16.7 Milliseconds) In general, everyone is quite clear that the response time of liquid crystals is very important for dynamic picture display, because in the case of LCD TVs, the transition time of a picture is about 16.7ms, so the response time of LCD TVs can be Cannot be shorter than 16.7ms, it is very important for the picture performance of dynamic picture. However, there is also a case where the blur does not disappear even if the response time of the liquid crystal is 0 ms (this is unlikely and difficult). This is because the LCD screen uses the "Hold mode" method to display images. According to some experiment reports, we can see that the animation displayed on the screen using the “Hold†method will shake right and left on the retina. When this kind of shaking accumulates over time, it feels that the dynamic picture is blurred. Just like improving the response time of LCDs, it is necessary to develop a display method that shortens the “Hold†time. According to the above situation, the dynamic picture appearing on the liquid crystal screen is ambiguous and cannot be represented by the long-term measurement used, that is, the response time of the liquid crystal from white to black and black to white.
Improved Blur of Motion Picture Due to Hold Time <br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> If the ideal control type LCD panel with a response time of 0ms (Hold time 100%), MPRT is 16.7ms (frequency is 60Hz). When the Hold time is 50%, the MPRT is about 8.3ms; when the Hold time is 25%, the MPRT is 4.2ms. For a typical LCD, its MPRT is below 8ms; if it is a LCD with a high-quality image for commercial products, its MPRT can be estimated to be less than 4ms. As described above, the MPRT contains two major elements: the response time of the liquid crystal and the hold time. Therefore, if the image display quality is to be satisfied, the response time of the liquid crystal is desirably smaller than the above value. In the method of improving the response time of the liquid crystal, there are high-speed dynamic modes such as OCB, IPS, and VA, and also Over-drive drives and the like. Now, LCD TVs that focus on quality have put these methods into production. There are two ways to improve the blurring of the motion picture caused by the Hold time. One is to use the screen frequency to light off the backlight source, and the other is to use the motion compensation technology of the double speed display method. A first specific method to achieve this is to use backlight flicker and black signal insertion. Among the two technologies, the most interesting one is the dynamic compensation technology. Intermittent display methods such as backlighting and black signal insertion can improve the blurring of dynamic images and are relatively simple to implement. However, in the case of a large screen and a high brightness, the screen is liable to flicker. In contrast, the dynamic compensation double-speed display method can improve the dynamic picture blur without increasing the screen flicker, but it is still not easy to implement because of the large-scale signal processing circuit.
Japanese companies publish to improve image quality by shortening Hold time <br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> For example, there are 32-inch WXGA LCD TVs produced by Japanese companies using dynamic compensation high-speed display technology. The method is to use dynamic compensation technology to increase the picture signal and the driving picture frequency from the general 60Hz to 90Hz, shorten the Hold time to about 70%, and shorten the scanning time to 70% using the scanning backlight, and shorten the total. 50%. On the premise that the screen flicker is not increased, the dynamic picture blurring problem is improved. Because the backlight is turned off at 90 Hz, flickering of the screen is not easily perceived by human eyes. In addition, there are other companies who also use motion compensation technology to increase the picture frequency to 120Hz to improve dynamic picture quality.
Currently, mainstream LCD backlights use CCFLs (Cold Cathode Fluorescent Lamps) that have a short lifetime, which is a flaw in LCDs. Fortunately, people have now found its successor, the LED. The defects of the traditional CCFL backlight In order to understand the LED backlight technology, we need to understand the current backlight technology problems. We know that liquid crystal is a substance that is between the liquid and the crystal. The wonderful thing about liquid crystals is that they can change the state of their molecular arrangement through current, and applying different voltages to the liquid crystal can control the amount of light passing through, thus displaying a wide variety of images. However, the LCD itself does not emit light, so all LCDs require backlighting. Currently, LCD backlights are almost all CCFLs (Cold Cathode Fluorescent Lamps).
Because the cold cathode fluorescent lamp is not a planar light source, in order to achieve a uniform luminance output of the backlight, the backlight module of the LCD must be matched with a plurality of auxiliary devices such as a diffusion sheet, a light guide plate, and a reflection plate. Even so, it is still very difficult to get a uniform luminance output like a CRT. When most LCDs display full white or dark screens, the difference between the screen's edge and the center brightness is very obvious.
In addition to the complex structure and poor brightness output uniformity, the use of CCFL as an LCD backlight source has a problem that has a short life span. Most CCFL backlights have a very noticeable drop in brightness after 2 to 3 years of use (lifetimes range from 15,000 hours to 25,000 hours). Many LCDs (especially laptops) display screens yellow after a few years of use. The dark phenomenon, which is caused by the shorter decay period of the CCFL.
At the same time, since the CCFL backlight must include complicated optics such as diffusers and reflectors, the volume of the LCD cannot be further reduced. In terms of power consumption, LCDs using CCFLs as their backlights are also unsatisfactory, and CCFL backlights for 14-inch LCDs often consume 20 W or more. For laptops and portable devices, their endurance will be a major test.
In order to solve these CCFL flaws, almost all LCD manufacturers have begun to look for better LCD backlights. Because LED has ultra-low power consumption, extremely long working life and simple structure, it quickly gained the favor of LCD manufacturers. So what is LED? What's so wonderful about it?
In fact, LED (Light Emitting Diode, light emitting diode) is not a cutting-edge technology product. It can be seen everywhere in our daily life: colorful billboards on roadsides, different colors of household appliances, and backlighting of mobile phone buttons. Car headlights, etc., have adopted LED as a light source.
After the LED was born in the 1960s, it was recognized as the terminator of lighting equipment such as fluorescent tubes and light bulbs. Some people even thought that LED will create a new era of lighting and eventually appear in all occasions where lighting is needed. The working principle of the LED is completely different from our common incandescent and fluorescent lamps. The LED is essentially a semiconductor device.
The core of the LED is a wafer consisting of a P-type semiconductor and an N-type semiconductor. At the interface between the P-type semiconductor and the N-type semiconductor, a thin layer with special conductive properties appears, which is commonly known as PN Junction Transistors. ). The PN junction can generate resistance to the diffusion motion of majority carriers in P-type semiconductors and N-type semiconductors. When a forward voltage is applied to the PN junction, current flows from the anode of the LED to the cathode, and the minority carriers in the PN junction. Most carriers are recombined, and excess energy is converted into light and released. LED is based on this principle to achieve the conversion of electricity and light. According to the different physical properties of semiconductor materials, LED can emit light from different wavelength bands and different colors from ultraviolet to infrared.
Cold Cathode Fluorescent Lamp (CCFL)
Traditional LCD monitors use CCFL (Cold Cathode Fluorescent Tube) backlights. There are two kinds of CCFL backlight design: “side-in†and “straight-fallâ€, but the side-entry type makes the light breakage rate higher due to the light guide design, which in turn limits the brightness of the backlight. The brightness increases when the panel size increases. The lower it is, it is only suitable for 8-inch to 15-inch TFT LCD panels, which are used by individuals such as Laptops and Desktops. However, when viewing large LCD TVs at home, the brightness of the side-entry type will be difficult to meet. Straight fall.
However, the larger the size of the LCD, the higher the proportion of the cost of the backlight module, which is referred to is the straight-type CCFL backlight module, according to statistics, is also the use of straight-type CCFL backlight module, in 15 The backlight module only accounts for 23% of the overall cost in inches, but it increases to 37% by 30 inches, and when the 57-inch resolution is estimated, the cost of the backlight module will reach 50%. Therefore, the straight-down CCFL backlight is only suitable for medium-size LCD TVs with a size of about 30 inches, and is not suitable for use in larger area designs. At the same time, the CCFL uses mercury gas discharge to generate lighting. Although the current EU RoHS regulations are acceptable as long as the “mercury†dose is below the standard, no one can guarantee that the standard may be raised to zero in the future (completely inaccurate). Use), CCFL will not be available at that time, or it must be diverted to non-mercury CCFL.
Even if the mercury-free CCFL is technically feasible, the CCFL is still a closed-tube gas-discharge type electronic lighting. The resistance of the light pipe to external forces is limited, and a large collision will cause the light pipe to break and cause lighting failure. Other solid-state electronic lighting (such as LEDs) do not have this concern. In addition, because it does not need to use light guide plate, but also less light loss problem, so does not need brightness enhancement film, especially brightness enhancement film is a minority of patented technology, expensive, straight-type can be omitted Light plates and brightness enhancement films help reduce costs.
However, the straight-down type CCFL also has its disadvantages. In order to enhance the brightness of the screen, the number of light pipes must be increased. However, the result of close arrangement of the light pipes will be unfavorable for heat dissipation. Since the distance between the left and right spaces is reduced, the heat dissipation has to be increased from the thickness level. Space, however, the increase in thickness also equals some of the advantages of LCDTV: Thinness. Incidentally, the use of CCFL tubes on large-inch LCD TVs, the length of the light tube must also increase in response to the increase in the number of inches. However, in the case of longer CCFL tubes, the intermediate positions and ends of the light tubes will be The problem of luminance MURA and color MURA is prone to occur, which in turn affects the light uniformity of the backlight. In order to maintain the light uniformity continuously, the diffusion film is used to enhance the light uniformity, but the diffusion film also brings about a loss of light transmittance. To reduce the brightness, the result of the decrease in brightness has to be reinforced by increasing the number of light pipes, but as mentioned before: adding a light pipe will make it more difficult to design heat dissipation, increase the thickness of the backlight module, or even increase the power consumption, according to Understand that the power consumption of CCFL backlight modules has accounted for 90% of the total power consumption of LCD TVs. Therefore, changing the backlight technology is currently one of the directions for changing the LCD image quality.
Light Emitting Diodes (LEDs)
Since the CCFL backlight has many side-effect concerns, the industry has also sought various new backlight implementation technologies, and LED is one of the feasible solutions, such as Sony's Qualia series television, which is the high-end large size (40 inches, 46 inches) LCDTV, its backlight part is composed of WLED, called WLED backlight technology. The development of LCD monitor for LED backlight technology has also reached a substantive stage. We can already see the relevant product display at the 2007 CES exhibition.
LED backlighting has several advantages. The first is solid-state electronic lighting. It has higher resistance to collision than CCFL, and there are no concerns about the environmental regulations of mercury gas. There is no concern about UV-UV leakage, and at the same time it exceeds the saturation of color and lifespan. CCFL, the other LED can be driven as long as the forward voltage, unlike CCFL need to exchange the positive and negative voltage, even if only the positive drive voltage, LED's demand level is also lower than the CCFL. In addition, the brightness of the LED can be adjusted only by Pulse Width Modulation (PWM), and the same method can be used to suppress the afterimage problem on the TFT LCD display. However, the brightness adjustment of the CCFL is more complicated and cannot be performed. Inhibition of afterimages must be suppressed in a different way.
Although LED backlighting has many advantages, it also has its disadvantages. The first is the luminous efficiency. In terms of the same power consumption, LEDs are not CCFLs, so the heat dissipation problem is more serious than that of CCFLs. In addition, LED is a point light source, and the CCFL line type. Compared with light sources, it is more difficult to control the light uniformity. In order to achieve the best possible light uniformity, the resulting LEDs must be carefully selected for their characteristics, and a large number of consistent (wavelength, brightness) LEDs should be used for the same backlight. Among them, this selection cost is also quite high. Fortunately, the LED's luminous efficiency is still rising, and now it has been able to reach more than 100ml/W, so that the color saturation can be better, and the backlight WLED arrangement is more relaxed, so that electricity and heat problems are relieved. After the continuous improvement of the manufacturing yield rate, the cost of selecting the LED with the same bright characteristics will also decrease.
Just changing the backlight technology may not be enough to trigger the LCD revolution, so let's go look at other LCD technology development. OLED (Organic Light Emitting Diode) is an organic light-emitting diode. OLED display technology differs from traditional LCD display methods in that it does not require a backlight, uses a very thin coating of organic material and a glass substrate, and these organic materials emit light when current passes through them. Moreover, the OLED display screen can be made lighter and thinner, have a larger viewing angle, and can significantly save power. However, its current life and price limit its bottleneck in LCD development.
OLED is another high-profile panel application technology, and the implementation of small-size panels is an early stage. According to the customer's plan, there will be more models available from 2008 to 2009, but it will still be dominated by sub-panels, and even if there is a significant increase in aircraft types and shipments, the market share will not exceed. 10%. Because OLEDs are inherently thin, the conditions of comparison, viewing angles, and power saving are superior to those of TFT-LCDs, and they have always been valued by the industry. They believe that OLEDs will replace TFT-LCDs and have invested heavily in R&D for several years. However, on the one hand, the OLED technology encounters bottlenecks, and the lifetime problem needs to be overcome. On the other hand, the TFT-LCD technology continues to advance, and now it can also provide excellent contrast and perspective, resulting in OLED demand can not be greatly improved, and the market is small and oversupply , limited to price competition; originally invested in the industry can not escape the fate of dissolution and downsizing. In the past, Taiwan Shenghua Technology invested in the establishment of Shengyuan into OLED research and development. Seeing that OLED and TFT-LCD cannot compete with each other, especially the cost difference, TFT-LCD in the specifications can easily reach a viewing angle of 170 degrees, a contrast ratio of 500:1, and brightness. Increase, you can also do thin, although the reaction rate is inferior, but it can reach the range acceptable to the human eye. Therefore, the Shengyuan Garden has also been closed down, leaving only a few R&D personnel to return to Shenghua to develop materials. In the future, if OLED lifetimes and prices can be greatly improved, there are still opportunities; at this stage, products with particular characteristics and emphasizing innovations are required; the large amount of time has not yet been seen.
The AMOLED (Active Matrix/ Organic Light Emitting Diode) active matrix organic light-emitting diode panel (AMOLED) is called the next-generation display technology. Samsung Electronics, Samsung SDI, and LG Philips all attach great importance to this new display technology. At present, Samsung Electronics Co., Ltd. and LG.Philips Philips Electronics are the main directions for developing large-size AMOLED products. Judging from the product performance of current finished products, if the cost of AMOLED can be effectively controlled, the traditional LCD panel technology will be greatly challenged.
One of AMOLED's advantages: No need for backlight AMOLED One of the advantages: More color saturation AMOLED One of the advantages: It can achieve 180 degree viewing angle of IPS or VA panel. One of the advantages of AMOLED: Effectively solve the problem of LCD panel dynamic blurring in the above Of the four OLED advantages, we are particularly concerned about the fourth product feature, because in the current market all desktop LCD monitors, can not solve the LCD screen dynamic blur problem. The blurred motion picture of the LCD screen usually refers to the phenomenon that the contour of the edge is blurred in the process of picture conversion. There are two reasons for the occurrence of the dynamic picture blur phenomenon. One is the response time of the liquid crystal and the afterglow of the phosphor, and the other is One is a TFT driver, just like the Hold mode image control.
Hold is the main cause of blurry images caused by dynamic <br> <br> so-called "Hold mode" display mode, the display is a Frame image within a certain period of time, while in the TV picture, this Hold time is equivalent to a vertical period (16.7 Milliseconds) In general, everyone is quite clear that the response time of liquid crystals is very important for dynamic picture display, because in the case of LCD TVs, the transition time of a picture is about 16.7ms, so the response time of LCD TVs can be Cannot be shorter than 16.7ms, it is very important for the picture performance of dynamic picture. However, there is also a case where the blur does not disappear even if the response time of the liquid crystal is 0 ms (this is unlikely and difficult). This is because the LCD screen uses the "Hold mode" method to display images. According to some experiment reports, we can see that the animation displayed on the screen using the “Hold†method will shake right and left on the retina. When this kind of shaking accumulates over time, it feels that the dynamic picture is blurred. Just like improving the response time of LCDs, it is necessary to develop a display method that shortens the “Hold†time. According to the above situation, the dynamic picture appearing on the liquid crystal screen is ambiguous and cannot be represented by the long-term measurement used, that is, the response time of the liquid crystal from white to black and black to white.
Improved Blur of Motion Picture Due to Hold Time <br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> If the ideal control type LCD panel with a response time of 0ms (Hold time 100%), MPRT is 16.7ms (frequency is 60Hz). When the Hold time is 50%, the MPRT is about 8.3ms; when the Hold time is 25%, the MPRT is 4.2ms. For a typical LCD, its MPRT is below 8ms; if it is a LCD with a high-quality image for commercial products, its MPRT can be estimated to be less than 4ms. As described above, the MPRT contains two major elements: the response time of the liquid crystal and the hold time. Therefore, if the image display quality is to be satisfied, the response time of the liquid crystal is desirably smaller than the above value. In the method of improving the response time of the liquid crystal, there are high-speed dynamic modes such as OCB, IPS, and VA, and also Over-drive drives and the like. Now, LCD TVs that focus on quality have put these methods into production. There are two ways to improve the blurring of the motion picture caused by the Hold time. One is to use the screen frequency to light off the backlight source, and the other is to use the motion compensation technology of the double speed display method. A first specific method to achieve this is to use backlight flicker and black signal insertion. Among the two technologies, the most interesting one is the dynamic compensation technology. Intermittent display methods such as backlighting and black signal insertion can improve the blurring of dynamic images and are relatively simple to implement. However, in the case of a large screen and a high brightness, the screen is liable to flicker. In contrast, the dynamic compensation double-speed display method can improve the dynamic picture blur without increasing the screen flicker, but it is still not easy to implement because of the large-scale signal processing circuit.
Japanese companies publish to improve image quality by shortening Hold time <br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> For example, there are 32-inch WXGA LCD TVs produced by Japanese companies using dynamic compensation high-speed display technology. The method is to use dynamic compensation technology to increase the picture signal and the driving picture frequency from the general 60Hz to 90Hz, shorten the Hold time to about 70%, and shorten the scanning time to 70% using the scanning backlight, and shorten the total. 50%. On the premise that the screen flicker is not increased, the dynamic picture blurring problem is improved. Because the backlight is turned off at 90 Hz, flickering of the screen is not easily perceived by human eyes. In addition, there are other companies who also use motion compensation technology to increase the picture frequency to 120Hz to improve dynamic picture quality.
Currently, mainstream LCD backlights use CCFLs (Cold Cathode Fluorescent Lamps) that have a short lifetime, which is a flaw in LCDs. Fortunately, people have now found its successor, the LED. The defects of the traditional CCFL backlight In order to understand the LED backlight technology, we need to understand the current backlight technology problems. We know that liquid crystal is a substance that is between the liquid and the crystal. The wonderful thing about liquid crystals is that they can change the state of their molecular arrangement through current, and applying different voltages to the liquid crystal can control the amount of light passing through, thus displaying a wide variety of images. However, the LCD itself does not emit light, so all LCDs require backlighting. Currently, LCD backlights are almost all CCFLs (Cold Cathode Fluorescent Lamps).
Because the cold cathode fluorescent lamp is not a planar light source, in order to achieve a uniform luminance output of the backlight, the backlight module of the LCD must be matched with a plurality of auxiliary devices such as a diffusion sheet, a light guide plate, and a reflection plate. Even so, it is still very difficult to get a uniform luminance output like a CRT. When most LCDs display full white or dark screens, the difference between the screen's edge and the center brightness is very obvious.
In addition to the complex structure and poor brightness output uniformity, the use of CCFL as an LCD backlight source has a problem that has a short life span. Most CCFL backlights have a very noticeable drop in brightness after 2 to 3 years of use (lifetimes range from 15,000 hours to 25,000 hours). Many LCDs (especially laptops) display screens yellow after a few years of use. The dark phenomenon, which is caused by the shorter decay period of the CCFL.
At the same time, since the CCFL backlight must include complicated optics such as diffusers and reflectors, the volume of the LCD cannot be further reduced. In terms of power consumption, LCDs using CCFLs as their backlights are also unsatisfactory, and CCFL backlights for 14-inch LCDs often consume 20 W or more. For laptops and portable devices, their endurance will be a major test.
In order to solve these CCFL flaws, almost all LCD manufacturers have begun to look for better LCD backlights. Because LED has ultra-low power consumption, extremely long working life and simple structure, it quickly gained the favor of LCD manufacturers. So what is LED? What's so wonderful about it?
In fact, LED (Light Emitting Diode, light emitting diode) is not a cutting-edge technology product. It can be seen everywhere in our daily life: colorful billboards on roadsides, different colors of household appliances, and backlighting of mobile phone buttons. Car headlights, etc., have adopted LED as a light source.
After the LED was born in the 1960s, it was recognized as the terminator of lighting equipment such as fluorescent tubes and light bulbs. Some people even thought that LED will create a new era of lighting and eventually appear in all occasions where lighting is needed. The working principle of the LED is completely different from our common incandescent and fluorescent lamps. The LED is essentially a semiconductor device.
The core of the LED is a wafer consisting of a P-type semiconductor and an N-type semiconductor. At the interface between the P-type semiconductor and the N-type semiconductor, a thin layer with special conductive properties appears, which is commonly known as PN Junction Transistors. ). The PN junction can generate resistance to the diffusion motion of majority carriers in P-type semiconductors and N-type semiconductors. When a forward voltage is applied to the PN junction, current flows from the anode of the LED to the cathode, and the minority carriers in the PN junction. Most carriers are recombined, and excess energy is converted into light and released. LED is based on this principle to achieve the conversion of electricity and light. According to the different physical properties of semiconductor materials, LED can emit light from different wavelength bands and different colors from ultraviolet to infrared.
Cross Recessed Countersunk Head Bolts
Cross Recessed Countersunk Head Bolts,Cross Recessed Countersunk Screw,Cross Countersunk Self Tapping Screw,Cross Recessed Countersunk Head Tapping Screw
Jiangsu Jiajie Special Screw Co., Ltd , https://www.jiajiescrewcompany.com