Comparison of the advantages and disadvantages of four new high-definition display technologies

Emerging display technologies represented by LCD, PDP, DLP, and LCoS represent the direction of television technology development in the digital television era and are destined to become the terminator of cathode ray tube televisions. Digital television, especially high-definition television, is also destined to become the trend of world television development. With the development of my country's economic level, especially in response to the opportunity of the 2008 Beijing Olympic Games, the time when HDTV programs appear around us is not far away. The following will introduce the advantages, disadvantages and prospects of the four emerging display technologies of LCD, PDP, DLP, and LCoS.

LCD - Liquid Crystal Television

Compared with traditional tube TVs, LCD TVs have many advantages: 1. High display quality, no flicker; 2. No electromagnetic radiation; 3. Good picture effect, no deformation, a true flat display; 4. Good scalability of screen size. Currently, the largest LCD display can be as large as 65 inches, while the smaller ones can be used on digital cameras and mobile phones. Its size and weight are much smaller than CRT. 5. High clarity, can truly achieve the effect of HDTV; 6. Digital working mode, more perfect performance of digital image signals; 7. Low power consumption, only 1/10~1/7 of CRT TVs of the same area.

Compared with PDP TV, which is also a member of flat-panel TV, LCD TV has some advantages that PDP TV does not have:

Longer service life: The nominal service life of PDP displays is mostly 25,000 to 30,000 hours, and it is irreversible, which is much inferior to the 50,000 to 75,000 hours of LCD displays (which can be restored by replacing the backlight tube);

It consumes less power than PDP color TV and is more energy-saving;

As an important product in the integration of 3C industries, LCD TVs have attracted the participation of many IT manufacturers and home appliance manufacturers, which will help reduce the cost of LCD TVs and expand the market.

PDP - Plasma Television

In the family of flat-panel TVs, besides LCD, there is PDP. PDP, or plasma display, is one of the latest display technologies after LCD. PDP is a "self-luminous" flat-panel display technology. The core principle is similar to the principle of fluorescent light emission. Inert gas is injected into the vacuum glass (i.e., the discharge space), and then voltage is applied to make the gas in the tube discharge. The ion effect releases ultraviolet light, which irradiates the phosphor coated on the wall of the glass tube. The phosphor will be excited to emit visible light, and different phosphors will be excited to emit visible light of different colors.

As a self-luminous display technology, PDP does not require a background light source, so it does not have the viewing angle and brightness uniformity problems of LCD displays, but achieves higher brightness and contrast. The design of the three primary colors sharing the same plasma tube also avoids the convergence problem, allowing for very clear images.

From the current technological development, PDP has a huge advantage in screen size. In January 2004, Samsung announced that it had successfully manufactured an 80-inch PDP panel. The thickness of this 80-inch (1766mm×1128mm) PDP is only 89mm, and the standard resolution is 1920×1080, which fully reaches the resolution level of high-definition television. It has a brightness of 1000nits and a contrast ratio of 2000:1, which has changed the previous problem that the brightness and contrast of large-size PDPs cannot be in the best state at the same time.

In addition to the advantages of brightness, contrast and viewing angle, PDP technology also avoids the response time problem in LCD technology, and these characteristics are crucial factors in dynamic video display. Therefore, from the current technical level, the advantages of PDP display technology in the field of dynamic video display are more obvious, and it is more suitable for use as a TV or home theater display terminal. PDP also has the advantages of ultra-thin, light weight, wide viewing angle (greater than 1700), etc., and PDP also adopts a completely digital drive method, which is a real "digital" TV.

Unlike several other emerging display media, PDP can only be used as a direct-view TV, and cannot be used as an image source for projection TVs to provide a larger picture like LCD, DLP, and LCoS. Since PDP is composed of millions of light-emitting tubes, it consumes a lot of power. A 42-inch model often consumes more than 300W of power. Heat dissipation is one of the biggest problems. Its service life is also the shortest among several emerging display technologies, and once damaged, it cannot be repaired. Since the glass on the plasma display is extremely thin, its surface is fragile and cannot withstand too much atmospheric pressure changes, let alone unexpected heavy pressure.

South Korea has an advantage in the production of large-size PDP panels in the world's PDP industry. Although Japan's PDP industry lags slightly behind in the development of the largest display panels, it has the most complete specifications for 37-50 inch PDP products and is at the upstream of PDP manufacturing-related industries.

DLP – Digital Light Processor

DLP technology is a fully digital display solution developed exclusively by Texas Instruments (TI) of the United States. It is one of the most advanced and mature display technologies in the field of digital television. The market share of DLP technology in the entire projection display field has exceeded 30%.

At the heart of DLP technology is the digital micromirror device (DMD), a semiconductor device the size of a thumbnail. The DMD consists of 1.2 million (for standard definition TV) or 2 million (for high definition TV) or even more (for digital movie projectors) microscopic mirrors that act as optical switches. Each mirror can flip back and forth (open or close) up to 5,000 times per second. The input image or graphic signal is converted into digital codes, that is, binary data consisting of 0s and 1s. These codes are then used to drive the DMD mirrors.

When the DMD base plate works with the projection lamp, color wheel and projection lens, these flipping mirrors can reflect a seamless digital image onto the TV screen. A DMD is composed of many tiny square reflective lenses (micromirrors for short) arranged closely together in rows and columns, and then attached to the electronic nodes of a silicon chip. Each micromirror corresponds to a pixel in the generated image. The number of micromirrors determines the physical resolution of a DLP projector.

The micromirror is controlled by the corresponding memory to switch and rotate between two positions of +100 angle and -100 angle. When the micromirror is at +100 angle, it is in the open position, and the light projected by the light source is reflected by the micromirror and projected onto the projection screen through the projection lens, generating bright pixels in the image; when the micromirror is at -100 angle, it is in the closed position, and the light cannot be reflected onto the projection screen, generating dark pixels in the image. At present, DLP projectors are divided into single-chip DLP projection systems and three-chip DLP projection systems according to the number of DMD devices in them.

In a DLP projection system, full color in the projected image is produced by a color filter wheel that rotates at a high speed of 60 rpm. The color filter wheel is composed of three color blocks: red, green, and blue (RGB). After the white light emitted by the light source passes through the rotating RGB color filter wheel, the red, green, and blue lights in the white light will alternately illuminate the DMD surface in sequence.

When one of the three colors of red, green and blue is irradiated onto the DMD surface, all the micromirrors on the DMD surface will switch between the on and off positions at high speed according to the presence or absence of this color of light in the corresponding pixel, and the number of times each micromirror switches to the on position is determined by the number of this color in the corresponding pixel. After being reflected by the micromirror, the light of this color is projected onto the projection screen through the projection lens. Similarly, when the light of the other two colors reaches the DMD surface, all the micromirrors will repeat the above actions. Since all actions are completed in a very short time, a full-color image is formed in the human visual system.

In a three-chip DLP projection system, three DMDs are used, each of which reflects one of the three primary colors of red, green and blue (RGB), and a color filter wheel is no longer used.

DLP has many technical advantages:

DLP is a truly digital display device due to its inherent digital nature.

The digital nature of DLP can achieve image quality with accurate grayscale and color reproduction. Compared with transmissive LCD, because it is based on reflective DMD, it does not require polarized light and is more efficient;

As a reflective device, it has over 60% optical efficiency, making DMD systems more efficient than LCD projection displays. This efficiency is the result of reflectivity, fill factor, diffraction efficiency and the actual lens "on" time;

Since each micromirror can flip more than 5,000 times per second, there is no response lag problem that exists in LCD, so it is more suitable for television and movies;

Seamless image advantage: the micromirror area on the DMD is 131μm2 or even smaller, and each interval is only 1μm. Unlike LCD and PDP, there is no large pixel structure, so the reproduced image is more perfect;

High reliability, the DLP system structure is solid and reliable, and its service life far exceeds that of various TVs such as cathode ray tubes, LCDs, and PDPs. The service life of DMD can reach 20 years.

In the United States, DLP accounts for about 15% to 20% of the entire rear projection market, and there are reports that it has exceeded 30%. The xHD3 DLP rear projection prototype with 1080p resolution and 5000:1 contrast ratio has appeared on the CES 2004 booth and will be mass-produced at the end of 2004. In the United States, the current DLP market is basically dominated by Korean manufacturers.

LCoS – Liquid Crystal on Silicon

LCoS, short for Liquid Crystal on Silicon, is a new digital imaging technology. Its imaging method is similar to that of three-chip LCD technology. However, the light of projectors using LCoS technology is not transmitted through the LCD panel, but reflected to form a color image.

It uses a CMOS integrated circuit chip coated with liquid crystal silicon as the substrate of the reflective LCD, which is polished with advanced technology and then plated with aluminum as a reflector to form a CMOS substrate. The CMOS substrate is then bonded to a glass substrate containing a transparent electrode, and then injected with liquid crystal for packaging. LCoS places the control circuit behind the display device, which can improve the light transmittance, thereby achieving greater light output and higher resolution.

From a technical perspective, among the emerging display media, PDP has the bleakest prospects and the most limitations, while DLP and LCoS are the most promising. In terms of current technological development, LCoS is not as mature as DLP.

First of all, LCoS display technology involves multiple high-tech frontier fields, mainly VLSI design and process-related technologies, liquid crystal-related technologies, optical engine technologies, new optical disc technologies, image processing-related technologies, etc. Therefore, no company can master all the key technologies. However, DLP technology is mature and has occupied a large number of ordinary civilian video equipment fields. The price of DLP products with a resolution of 1024×768 is already very low, and DLP with a resolution of 2048×1024 can also be supplied to the market. Although it is currently mainly used in digital cinema projection due to price factors, with the application of 4000×2000 level DLP in digital movie projection, 2048×1024 level high-definition TV projectors will also be available. Secondly, the high-definition picture quality of the large screen brought by LCoS high resolution cannot be shown, which is indeed far from the mature technology of DLP. In the LCoS projection system, any defects in the optical engine, mechanical structure, system circuit and LCoS chip itself will affect the image display effect. Third, there is no unified standard for the development and production of LCoS microdisplays, the industrial chain has not yet been fully formed, and the industrialization of new technologies, joint processing, changes in technical solutions, etc., have made the low-cost advantages of LCoS systems not yet reflected. Although in theory, the cost of a three-chip LCoS projection system can be lower than that of a single-chip DLP projection system when the resolution, brightness and other functions are matched, there is still a long way to go to achieve this goal.

In the emerging display technology, it can be clearly divided into two camps. PDP and LCD are one technical direction, focusing on the development of the display device itself. DLP and LCoS represent another direction. They jump out of the framework of developing display media based on display devices and are based on microchip manufacturing technology. They are obviously not on the same level as the former in terms of technology and cost. Therefore, when PDP and LCD were divided into three parts by South Korea, Japan and Taiwan, it was not surprising that DLP was exclusively owned by TI in the United States. After all, the United States still dominates the field of chip manufacturers. At present, there are dozens of companies in the world actively developing LCoS microdisplay technology, but only Sony, JVC, Philips and Hitachi have launched a small number of related products.

Like DLP, LCoS has unlimited potential in the large-screen high-definition TV market. At the same time, due to the small size, low power consumption and low-temperature reinforcement of LCoS microdisplays, it can completely replace the early micro CRT in various military helmet displays. In the field of near-eye displays, it has unique advantages. Near-eye displays are a special application direction and market, and the target products include helmet displays HMD, mobile phone displays, wireless network terminals, wearable computer displays, etc. In the fields of military, medical, entertainment, etc., the potential technical connotation of LCoS microdisplays will form the core of various portable high-definition display technologies.

Outlook for other emerging display technologies

OLED, or organic light-emitting diode, is also called OEL by many manufacturers and organic EL by Sony. OLED is known as the next generation of flat panel display technology. Currently, finished products of about 2 inches have begun to be used in products such as digital cameras and mobile phones, but there is still a long way to go to launch mature consumer products in the field of televisions.

OLED TVs do not require the light source required by LCD TVs, and have the high definition of plasma TVs, and the screen is thinner, and can even be made into a 1mm thick roll. The raw materials of this type of TV are relatively cheap, and plastic, polyester film or film can be used as the substrate. It does not require a light source, and its price will definitely be lower than plasma TVs and LCD TVs in the future.

Currently, Sanyo has produced mobile phones using OLED screens; Sony has also been developing OLED TVs, claiming that it will launch samples of about 13 inches in 2005. In 2003, IETECH in Taiwan successfully developed a 20-inch OLED display, allowing people to see the potential of OLED in the field of large-screen displays.

FED, or field emission display technology, is also a future large-screen display technology favored by many manufacturers. It is a display technology with a long history but relatively slow progress. The theory of field emission electrodes was proposed as early as 1928, but it was not until 1968 that research on the application of field emission electrodes in displays began. In 1991, the first FED display product was exhibited by a French company.

The display principle of this technology is similar to that of CRT, where the cathode emits electrons and hits the fluorescent screen to emit light. However, the cathode ray tube in FED is replaced by a field emission array flat cathode, so the display consists of two parts: a flat cathode and a fluorescent display screen, achieving flat display. FED has achieved the thin and light structure of a flat panel display while inheriting the high performance of CRT, achieving high brightness, high response speed, true color, and wide viewing angle, while avoiding the electromagnetic radiation and X-ray radiation of CRT.

In 2002, Samsung had developed a 32-inch FED panel. In the same year, ISE Electronics exhibited a 40-inch FED panel. In 2003, Motorola successfully developed a FED panel using carbon nanotubes. In addition to the 15-inch samples that have been released, it will also step up the trial production of 30-inch products. When producing large-size panel modules over 30 inches, the cost can be reduced by about 30% compared to LCD panels. FED has also begun its large-screen application process.

The GLV display system, or "grating light valve" imaging system, is a new type of high-precision photoelectric modulator. It was developed by CLM in the United States and transferred to Sony in 2000 due to financial difficulties. The GLV grating light valve is a device that relies on electrostatically driven micro-mechanical components to control the intensity and reflection direction of the incident light, and belongs to the "microcomputer electronic system". GLV is a linear array silicon chip device that can only produce a vertical linear array of pixels. To turn it into a flat image, it still relies on optical scanning methods. The number of vertical pixels in a TV image is determined by the number of pixels of the GLV linear array device. The GLV developed by Sony is a one-dimensional screen device with 1080 pixels arranged in vertical columns. The laser band reflected by 1080 groups of GLV gratings is then projected onto the screen with an optical prism for horizontal rotation, forming a 1920×1080 high-definition TV image.

The number of horizontal pixels is determined by the row pixels of the TV signal added to the grating. Each GLV chip is 20μm long and 5μm wide. The GLV grating modulator has a relatively simple structure. By using different projection light paths, it can be used to form a rear projection TV with a thickness similar to that of a plasma TV, or a front projection device. However, this technology is still in the experimental stage.

The disappearing terms in emerging television

In the emerging display media, many concepts will even disappear without a trace. The terms that were constantly hyped by some businesses and talked about by some enthusiasts in the promotion of cathode ray tube TVs will no longer exist.

Progressive scan: This term is exclusive to cathode ray tube televisions. For emerging display media such as LCD, PDP, DLP or LCoS, the image transmission and display are all complete images, without so-called line structure.

Magnetization: This is also a concept exclusive to CRT TVs. For LCD, PDP, DLP or LCoS, there is no need to worry about magnetization.

Geomagnetic correction: For large-screen CRT TVs, due to the influence of geomagnetism, it is required to consider the direction when placing them, otherwise the image will have some problems, affecting normal viewing. Better TVs are equipped with geomagnetic correction

Physically flat: For CRT TVs, in the so-called flat state, almost all TVs have problems with pincushion distortion and inaccurate convergence. However, new TVs such as LCD, PDP, DLP and LCoS are all flat and do not have the above defects.