The main technologies of projectors include CRT (Crystal Ray Tube: Cathode Ray Tube), LCD (Liquid Crystal Display: Liquid Crystal Display) and DLP (Digital Light Processor: Digital Light Processor). CRT and LCD projectors use transmissive projection, while DLP uses reflective projection. CRT and LCD projectors have mature technology, long application time, and stable performance. The DLP projector has been in use for a short time and the technology needs to be further improved. However, this projector uses micro-mirror reflection projection technology, which significantly improves the brightness and contrast, significantly reduces the size and weight, and has strong vitality and long-term market potential.
Original: CRT scanning projector
CRT projector can be said to be the originator of projectors. A CRT projector is also called a three-gun projector. Its working principle is no different from that of a CRT monitor. Its light source and imaging are both CRT. Although the working characteristics of CRT projectors are essentially different from those of LCD, DLP and other projectors, and CRT projectors and LCD projectors are both transmission projectors, CRT projectors emit light themselves, which are scanned and shot by cathode ray electron beams. On the imaging surface, the phosphor on the imaging surface is made to emit light to form an image, which is then transmitted to the projection surface. Therefore, CRT projectors have all the advantages and disadvantages of imaging in CRT technology. That is to say, CRT projectors have high resolution, good contrast, good color saturation, strong signal compatibility, and the technology is very mature. In particular, the brightness of CRT projectors has been greatly improved after adopting the new CRT shadow mask with current advanced technology. But CRT projectors, after all, use phosphors on the imaging surface to emit light and then project it onto the screen. When the number of effective scanning electrons increases to the saturation state, the amount of phosphor light emitting will not increase much if the number of effective electrons is increased. Therefore, in terms of brightness, CRT projectors are much lower compared to other types of projectors, which has always been the main factor that has plagued CRT projectors. However, CRT projectors have high resolution, good contrast, good color saturation, strong signal compatibility, and very mature technology. In addition, CRT projectors have scanning imaging characteristics and have excellent performance in resolution, brightness, contrast, saturation, and linearity. , pincushion, trapezoid, etc. have adjustment functions. CRT projectors play a role that cannot be replaced by other projectors in the aerospace and remote control monitoring industries, so they are used in relatively high-end professional fields
Mainstream: LCD LCD projector
LCD projector is a product of the combination of liquid crystal display technology and projection technology. It uses the electro-optical effect of liquid crystal to control the transmittance and reflectivity of the liquid crystal unit through circuits, thereby producing different gray Beautiful images with gradations and up to 1670 million colors. The main imaging device of an LCD projector is a liquid crystal panel. The size of the LCD projector depends on the size of the liquid crystal panel. The smaller the LCD panel, the smaller the size of the projector.
Based on the electro-optical effect, liquid crystal materials can be divided into active liquid crystals and inactive liquid crystals. Active liquid crystals have high light transmittance and controllability. The LCD panel uses active liquid crystal, and people can control the brightness and color of the LCD panel through relevant control systems. Like LCD monitors, LCD projectors use twisted nematic liquid crystals. The light source of LCD projectors is a special high-power bulb, and the luminous energy is much higher than that of CRT projectors that use fluorescent light, so the brightness and color saturation of LCD projectors are higher than that of CRT projectors. The pixels of LCD projectors are liquid crystal units on the LCD panel. Once the LCD panel is selected, the resolution is basically determined, so the resolution adjustment function of LCD projectors is worse than that of CRT projectors.
LCD projectors can be divided into single-chip and three-chip types according to the number of internal LCD panels. Most modern LCD projectors use 3-chip LCD panels (Figure 1). Three-chip LCD projectors use three liquid crystal panels of red, green and blue as the control layers of red, green and blue light respectively. The white light emitted by the light source passes through the lens group and converges to the dichroic mirror group. The red light is first separated and projected onto the red LCD panel. The image information represented by transparency "recorded" by the LCD panel is projected into the image. red light information.
The green light is projected onto the green LCD panel to form the green light information in the image. Similarly, the blue light passes through the blue LCD panel to generate the blue light information in the image. The three colors of light converge in the prism and are projected onto the screen by the projection lens. A full color image is formed on the projection screen. Three-chip LCD projectors have higher image quality and higher brightness than single-chip LCD projectors. LCD projectors are smaller in size, lighter in weight, have simpler manufacturing processes, higher brightness and contrast, and moderate resolution. The market share of LCD projectors now accounts for more than 70% of the overall market share, which is the largest share in the market today. The tallest and most widely used projector.
Rising star: DLP digital projector
DLP projector is an optical digital reflective projection device. The key imaging device of DLP projectors, DMD (Digital Micromirror Device), is a semiconductor element independently developed by Texas Instruments that can be controlled by two-bit pulses (Figure 2). The component features fast reflective digital switching capabilities for precise control of light sources. The basic principle is that after the light beam passes through a high-speed rotating three-color lens, it is projected on the DMD component, and then projected on the large screen through the optical lens to complete image projection. DLP projector is actually a fully digital reflective projection device based on DMD technology. A DMD is made up of many tiny square reflective lenses (referred to as micromirrors) that are closely arranged in rows and attached to the electronic nodes of a silicon wafer. Each micromirror corresponds to a pixel of the generated image. (Figure 3) Therefore, the number of micromirrors on the DMD device determines the physical resolution of a DLP projector. Usually when we say that the resolution of a projector is 600×800 SVGA mode, we refer to the micromirrors on the DMD device. The number is 600×800=480,000, which is quite complex and sophisticated. Each micromirror in the DMD device corresponds to a memory, which can control the micromirror to switch and rotate at an angle of ±10 degrees. Currently, DLP projectors are divided into one-piece DLP projection systems, two-piece DLP projection systems (Figure 5) and three-piece DLP projection systems according to the number of DMD devices in them.
DLP projectors use micromirror filter technology, using a chip composed of thousands of microlenses on the surface to switch light pixels at high speed to produce a projected image. The light beam forming the DLP image is not filtered, the energy is not reduced, and the projected image information is not lost. In addition, the DMD component has the advantages of reflectivity and tightness, and the utilization rate of light energy is much higher than that of traditional optical systems. With advanced optical architecture and high-quality optical lens design, DLP projectors can produce images with high definition, uniform picture, and good color reproduction. The brightness is higher than LCD images, and stripes and ghosting are less likely to occur than LCD projectors. few. DLP projection technology abandons convergence in the traditional sense. It can zoom at will and is very convenient to adjust. Moreover, its optical path is quite simple and smaller in size. Therefore, this technology is mainly used in ultra-portable systems. It is the lightest DLP ultra-portable projector in modern times. The weight can be less than 1.5kg. Of course, reducing the size also brings about defects in video display, which makes the video display effect of DLP projectors somewhat distorted. The optical and mechanical characteristics of DLP projectors also determine that their mobile anti-vibration performance is worse than that of LCD projectors. Like LCD projectors, DLP's pixels are also solidified, so its resolution adjustment function is poor.
Although the market share of DLP projectors is far lower than that of LCD projectors, as a new product, DLP projectors have inherent advantages in terms of size, weight and brightness, making them more suitable for modern e-commerce. In line with the needs of home theaters, especially its ultra-portable performance, it completely surpasses LCD projectors. DLP projectors have become the third category of products after CRT projectors and LCD projectors, with immeasurable application fields and market prospects.
Future Star: DLV Projector
The first three types of projectors work on completely different principles and complement each other in performance. In order to give full play to the advantages of various types of projectors, people thought of combining the advantages of CRT with the advantages of LCD and DLP, so projectors with DLV technology appeared.
DLV (Digital Light Valve: Digital Light Vacuum Tube, referred to as digital light valve) is a new technology that combines CRT transmissive projection technology and DLP reflective projection technology. The core of this technology is to use a small-diameter CRT as the imaging surface of the projector, and use a xenon lamp as the light source to shoot the image on the imaging surface to the projection surface (Figure 7). Therefore, while making full use of the high resolution and adjustability of CRT projectors, DLV projectors also take advantage of the high brightness and good color reproduction of xenon light sources. DLV projectors are not only a high resolution, contrast, color saturation A very bright projector. Its resolution generally reaches 1250×1024, and the highest can reach 2500×2000. The contrast ratio is generally above 250:1, the number of colors is generally 16.7 million 24-bit, and the projection brightness is generally 2000 to 12000 ANSI lumens, which can be used in large venues. used in.
Figure 7 DLA LCD panel
The LCD light valve projector uses a CRT tube and a liquid crystal light valve as the imaging device. It is a new type of combination of a CRT projector and a liquid crystal light valve. projector. In order to take full advantage of the high image resolution of traditional CRT projectors and overcome the shortcomings of poor brightness, its brightness can reach 6000 ANSI lumens and its resolution can reach 2500×2000. This type of projector is very suitable for use in situations with strong light and large audiences, such as very large command centers, conference centers and large entertainment venues. Of course, this type of projector is more expensive and larger, and the light valve is difficult to repair, so sales are limited