Foreword
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Liquid Crystal on Silicon (LCoS) is a relatively new and unfamiliar display technology that is now entering the HDTV market. What's really striking, however, is that the starting point for this technology is very high, not starting in the traditional way, using performance similar to the prior art, and then slowly taking the picture quality to a higher level. Among all display technologies, LCoS' resolution and contrast (for non-CRT displays) are the highest and images are the most natural. Some users are sensitive to image flicker, eyes are prone to fatigue, and LCoS has the highest refresh rate (120Hz), providing the smoothest and flicker-free picture. This article will delve into five LCoS HDTVs, all of which are prototypes, and hope to help you understand this evolving technology.
Of course, LCoS is not a new thing. It has been developed for more than a decade. JVC actually used this technology to produce high-end professional-grade projectors since 1998, but today the market is still relatively small. At the same time, this is also a very difficult technology to improve, many companies have to give up or have gone bankrupt. Thomson (using the RCA brand) produced the first commercial LCoS HDTV in 2001, Toshiba (using Hitachi LCoS chips) and Philips followed closely, but these companies stopped in October 2004. . Intel’s announcement in January 2004 that it began manufacturing LCoS chips shocked the industry, but it was discontinued in October 2004 and no results were achieved. Therefore, the prospect of LCoS has been questioned by many analysts. In fact, the technology is only integrating for the real entry into the HDTV market.
JVC launched its first rear-projection 1280×720 high-definition TV in July 2004, which kicked off the second-generation LCoS. Sony immediately launched the high-end 1920×1080 Qualia TV in January 2005, after which Brillian also Since the middle of 2005, it has provided 1280×720 TVs to the market. When I finished this article in early September, only a few LCoS HDTVs were available worldwide, but JVC and Sony just announced their second-generation HDTV, and LG also launched the first (using the TapoLight LCoS chip). Another major supplier, Hitachi, plans to launch LCoS HDTV at the end of 2005. Therefore, in this article we are fortunate to test and evaluate some pre-release prototypes. Here are some of the results we got.
Introduction to evaluation
Even if you are an expert, it is difficult to find a place to evaluate the image and quality of HDTV. In the exhibition or manufacturer showroom, the programs you see are most likely to be carefully selected, and may be fine-tuned to make each model perform better than normal. In the store showroom, viewing conditions, ambient light, video signal quality, and video source quality are often varied, and the results are not as good as they are, and HDTV itself is not optimal (sometimes because the previous customers adjusted the settings) So you usually see cartoons, because the more saturated colors and artificial drawings can give viewers a good illusion of TV.
The best way to evaluate the image and quality of any display technology is to put multiple TVs together, carefully control the various conditions, and test them one at a time, so that all TVs display exactly the same high-quality images. You need an ideal viewing environment, D6500 backlighting, superior video source, and a state-of-the-art video signal distribution system. Then, let the manufacturers send the best engineers and carefully adjust their TVs to achieve the best image and quality results. We did this for a whole month in July 2005. It was a time-consuming job, but the results were very interesting and definitely worth the resources.
This process is called "evaluation", it is not to be determined, but it is a great challenge for every display. Since each machine is very good when viewed alone, when it displays the same high-quality picture with other excellent models, many places are inferior, and even small differences can be very obvious. In the evaluation, we first tested these TVs with hundreds of DisplayMate's 1280×720 and 1920×1080 HDTV resolution test images. We used two advanced spectrum analyzers to carefully measure the luminosity of each TV. Chroma. During the test, we invited 34 reviewers to watch more than one hour of high-quality video programming, then compare and visually evaluate. Figure 1 shows the evaluation settings when the lights are on. These TVs line up along a 35-foot wall near my home theater.
Introduction to this article
The first part of this article first introduces the HDTVs that participated in the evaluation, and then introduces the overall situation of LCoS technology. The second part of this paper, Issue 103, December 2005, will continue to discuss how to conduct tests and then examine the luminosity and chromaticity of these TVs in detail. The third part, the 104th issue in January 2006, will first analyze the test image, then introduce the jury test, followed by the individual evaluation results of each machine, the LCoS technology evaluation results, and comparison with other display technologies. .
Please note that this article is the latest in a series of display technology reviews published by Widescreen Review from September to December 2004, in the 88th to 91st editions. The series covers CRT, liquid crystal television (LCD), plasma and DLP display technologies. The topics of the series are: first, basic parameters; second, gray field and color accuracy; third, display artifacts and image quality; fourth, display technology evaluation.
Participate in HDTV
There were only two LCoS HDTVs on the market when we planned to start the evaluation, so I decided to expand the sample size and persuade several manufacturers to lend me their valuable lab prototype for this article, in order to bring each LCoS The manufacturer's products (except for the color wheel) are included, and currently there are only five manufacturers: JVC, Sony, Brillian, eLCOS and SpatiaLight. There are other brands of LCoS HDTVs on the market, but they all use the devices offered by the above. We include two standard HDTV resolutions: 1280×720, approximately 1 megapixel, and 1920×1080, approximately 2 megapixels, which are referred to herein as 720 or 1080, respectively. (There is no need to follow the p that represents progressive scan, because all models are progressive scan, see below.)
JVC and Sony don't need to introduce again, but the other three are quite strange to most consumers. Brillian is a small startup company based in Tempe, Arizona, the only HDTV manufacturer in the United States. They provided a prototype of the 65å‹720 (currently available) and tried to provide one more 1080 before the evaluation. eLCOS is also a small start-up that partnered with light engine manufacturer JDS Uniphase, screen maker DNP, and video processor manufacturer Silicon Optix to provide a 56-inch 1080 lab demo. Please note that the model offered by the company cannot be called a prototype because it is not designed for mass production. SpatiaLight is also a small start-up that offers LCoS chips and driver circuitry, and was used in LG's new 71-inch 1080 HDTV in September 2005. SpatiaLight agreed to participate in the assessment but failed to provide the prototype in time.
JVC offers two: the Consumer Products Division sent their 61å‹720 HDTVs to market, with less than $4,000 in popularity, while the Professional Products Division sent them 48 for TV and film post-production.å‹ 1080 benchmark display prototype, its price positioning for the high-end professional market, designed to compete with Sony's high-end professional-grade CRT (we will compare it in the third part). Note that the LCoS technology used in the two models of the JVC is different. The normal type has a digital backplane that uses pulse width modulation to control each pixel (see Part III and below), while the professional stage uses analog voltage to control each pixel (see Below). Sony has launched 70å‹1080 Qualia 006 in January 2005, so we invited Sony, but the company refused to participate in the evaluation.
For details of the manufacturers involved in the evaluation, please refer to the HDTV manufacturer's introduction. Table 1 shows the basic information of each model. Note that the models in the table are arranged in alphabetical order by resolution. There are two sources of JVC Consumer prices listed on the list, one is the manufacturer's suggested retail price, the other is the lowest actual selling price I can find on the market, and the others will be available in the market at the prices listed in the table. .
LCoS technology
LCoS is the latest display technology for controlling the brightness of image pixels with liquid crystal. The most widely used form of liquid crystal technology is large amorphous silicon LCD chip, which is used for direct viewing of computer monitors, TVs and HDTVs. Typical sizes range from 5å‹ to 82å‹. The next application, August 31, 2005, will be a smaller, high-temperature polycrystalline chip for video and data projectors. These applications are only about one inch in size, and all will be used for large-screen LCD rear-projection TVs. HDTV. The light sources used in both technologies are behind the chip, and the light must pass through the chip to the front, including all the circuits and components that control the pixels within the chip, but these blocks block a lot of light and form a channel between the pixels. Therefore, the higher the resolution, the more problems there are. The second major problem is that the liquid crystals need to be relatively thick in order to get a higher contrast, which slows down the response time and thus creates smear when the graphics move or changes.
The basic principle of LCoS is to use a mirror behind the liquid crystal layer. The light enters the liquid crystal layer from the front and passes through the mirror to pass through the liquid crystal layer to hit the screen. This requires a slightly more complicated optical component, but it is very useful. It has several straightforward advantages, such as all electronic components behind the mirror, completely outside the light path. There is a lot of space behind it, which can lead to incredible high resolution, and LCoS has the highest resolution in all display technologies. In addition, because the light passes through the liquid crystal twice, it can achieve high contrast but is still very thin, which greatly improves the response time and reduces the smear. We will discuss the advantages and disadvantages of LCoS in the third part.
So how does it work? The liquid crystal can deflect the polarization of the light, and the amount of deflection can be controlled by the electric field. The silicon wafer behind the lens produces an electric field that controls each pixel. In fact, the lens is the top layer of the silicon wafer, and the liquid crystal is directly mounted on the lens, which is why it is called "silicon-based liquid crystal". Most chips are three-quarters of an inch in size, and Figure 2a shows a photo of an LCoS chip. When an image is generated, the polarized light is focused on the chip, and its brightness is controlled by transforming the electric field behind each pixel. The electric field deflects the light and then blocks the deflecting portion with a polarizing filter. The silicon-generated electric field actually works like a computer memory chip, organized in rows and columns of pixels, each pixel has an address, just like the memory location, Figure 2b shows a cross-section of an LCoS.
As with other display technologies, each manufacturer has their own implementation method and will take a special name, as shown in Tables 1 and 2. All manufacturers have indicated that they use vertically distributed liquid crystals with inorganic alignment layers that are vertically aligned to increase contrast and give the screen a natural black color when the drive signal is zero. The inorganic alignment layer avoids the problem of aging of the early organic alignment layer, so all of these LCoS technologies have a long life.
Table 1: HDTV models participating in the assessment.
Table 2 lists the specifications of each manufacturer's 1080 LCoS chip. In order to make the information more complete, we include Sony and SpatiaLight products that did not participate in the evaluation. There are two sources of Sony information, one is the first generation of chips in Qualia 004 and 006, and the other is the second generation of chips in the XBR product launched in August 2005.
Table 2: Performance Indicators for 1920 x 1080 LCoS Chips
Chip contrast may be the most important value in the table, because the HDTV screen contrast is always smaller than the chip's value. The pixel pitch is the distance between the center and the center of the pixel on the chip, and the pixel gap is the invalid space between them. The aperture ratio is the percentage of the effective pixel area. Since it is close to 100%, the gap between pixels on the screen is usually not noticed. The aperture ratio of LCoS is a few percent higher than that of DLP, and the high-temperature polysilicon liquid crystal projector chip usually has a small value of only 50 to 70 percent, so its pixel structure can usually be seen. Life expectancy includes a variety of factors, but can only be estimated through laboratory test inference, all manufacturers provide more than 100,000 hours of value, that is, if you open 24 hours a day for more than 11 years. The main concern is the loss of brightness and contrast over time, also known as aging, which leads to the so-called image burn-in, but all manufacturers have stated that aging and burn-in are not produced in the inorganic alignment layer.
The signal level refers to the number of data bits in the chip line control LCoS chip. The higher the number of bits, the smoother the gray field, and the less likely the chromatic aberration line appears.
Response time is a standard in the industry that represents the time from pixel black (to rise time or Ton) plus the total time from white to black (fall time or Toff). The response time is to measure the image transformation speed and provide a moving image. The visibility of moving smear is usually as small as possible, but moving smear involves multiple factors. Unfortunately, some manufacturers provide response times that are average rise and fall times, not their sum, making the display value twice as fast as the actual one. So pay great attention to the response time indicator, make sure you know which method is used by the manufacturer. (For example, Sony's Qualia SXRD chip uses a total response time of 5ms, but the latest XBR SXRD chip uses an average time of 2.5ms as the response time, so the value is twice as fast, but it is not.) The rise and fall times are listed in the table to show the actual situation.
The physical process of controlling the brightness of each pixel, whether it is LCoS or all other liquid crystal technology, is actually an analog technology, which is an advantage, because human vision is also an analog process that avoids image jitter in all digital display technologies such as DLP and plasma. (See series three, four and the third part of this article). However, it is actually possible to design the silicon backplane of the chip to be driven by analog voltage or digital signal pulse width modulation PWM. Their end result is still a liquid crystal simulation display, but this is done in two completely different ways, each with different strengths and weaknesses, which we will discuss later. (Digital methods similarly to lamp dimmers use electronic pulse control to simulate tungsten lamps.) The device control techniques in Tables 1 and 2 list the methods used for each type of application. Digital backplanes typically produce higher yields and are cheaper to manufacture ( But not all manufacturers agree with this view, and the drive circuit is cheaper. But it is still difficult to get a smooth ash field with digital technology (especially in the dark field), so this is why many models use analog backplanes.
Optical and electrical components
In addition to the chip, the LCoS HDTV has other key components, such as a lamp engine that includes all the optics from the bulb to the projection lens. It first prepares the beam, illuminates the tiny LCoS chip, and then magnifies the image with a linear scale factor of about 80 to 1, with an area magnification of about 6,400 to 1 (for example, a 60-inch screen). The technology involved here is not equal to the LCoS chip itself, it is equally important for the quality of the image seen on the screen, it is usually the most expensive component of the projection HDTV. Figure 2c shows a projection optical engine. Note that all of our HDTVs here use three LCoS chips, which correspond to the three primary colors of red, green and blue. The filter first divides the light into three basic colors for the LCoS chip, and then uses a set of prisms to recombine the basic colors into a beam of light in front of the projection lens. The screen is another important component of the optical system, which also has a large impact on the quality of the image. A good screen is quite expensive. There are also two very important optical components, one is the black internal space that absorbs stray light between the projection lens and the screen, and the second is the front surface flat mirror at the rear of the chassis, which can change the direction of the light path of the projection lens. To the screen.
Figure 2 (a) LCoS D-ILA chip, provided by JVC.
Figure 2 (b) A cross-sectional view of the LCoS D-ILA chip, courtesy of JVC Professional Products.
Figure 2 (c) Projection optics engine, supplied by Brillian.
There are also two circuit components we often mention, one is the chip line control part, responsible for the underlying direct control of all LCoS chips, the other is the front-end board, with all HDTV input interfaces, it will all other different input signals (composite video Signals, S-video, composite video signals, RGB, DVI, and HDMI are converted to the digital format required for chip lines. It also manages on-screen menus for user and service adjustments and controls. Chip circuitry is usually only factory controlled, including the low-level gamma meters needed to control the LCoS chip.
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