From the composition of projector products, it includes three main parts: core projection imaging module, optical engine, electrical control and interface. Among them, the core projection imaging component is the core of the projector product, which occupies a very important part in the cost composition of the whole projector product, and its position is quite similar to that of the processor in the computer.
Up to now, the development of projectors has mainly gone through three stages, which are realized by three typical display technologies, namely CRT projection technology, LCD projection technology and DLP projection technology developed in recent years.
1, CRT (cathode ray tube) three-gun projector
As an imaging device, CRT is the earliest and most widely used display technology. CRT projector can be said to be the originator of projectors.
CRT projector is also called three-gun projector, and its working principle is no different from CRT display. Its light source and imaging are CRT. The working characteristics of CRT projectors are essentially different from those of LCD and DLP projectors. It decomposes the input signal source into the fluorescent screens of R (red), G (green) and B (blue) CRT tubes, and the phosphor emits light, amplifies and converges under the action of high voltage, and displays color images on the big screen.
CRT projector has high resolution, good contrast, good color saturation, strong signal compatibility and very mature technology. In terms of brightness, CRT projectors are much lower. So far, its brightness value has been hovering below 300 lumens. At the same time, the operation of CRT projector is complicated, especially the convergence adjustment is cumbersome, and the body volume is large. It is only suitable for installation in a relatively fixed place with weak ambient light, and is not suitable for moving. Therefore, although the projector market once flourished in the early stage of development, CRT projectors are rarely used at present and basically quit the projector market.
2.LCD projector
Liquid crystal display technology is one of the leading technologies in the projector market at present. Liquid crystals include active liquid crystals and inactive liquid crystals. Inactive liquid crystals reflect light and are generally used in notebook computers and movie projectors. Active liquid crystal has light transmittance, and it is made into LCD panel for projector.
LCD projectors are divided into LCD panels and LCD light valves. Most of our common projectors are LCD flat panel projectors.
First, the LCD projector
The liquid crystal projector uses the electro-optical effect of the liquid crystal to control the transmittance and reflectivity of the liquid crystal unit through the circuit, thus producing beautiful images with different gray levels and as many as16.7 million colors. The light source of LCD projector is a special high-power bulb, and its luminous energy is much higher than that of CRT projector using fluorescence, so the brightness and color saturation of LCD projector are higher than that of CRT projector.
The size of LCD panel determines the structure and total volume of projector. The smaller the area of the LCD panel, the smaller the optical system of the projector, thus making the projector smaller.
At present, the panel sizes of LCD projectors on the market are mostly 1.32 inch (1 inch =2.54cm), 0.9 inch and 0.7 inch, which can support the physical resolution of SVGA and XGA. New LCD panels, such as 0.79-inch and 0.99-inch panels with high aperture ratio, have also begun to appear.
At present, there are only two suppliers of high-temperature LCD projection LCD panels in Japan: Epson and Sony.
The advantage of LCD projector is excellent color performance and high brightness, but the disadvantage is that the light efficiency is affected to some extent because of the projection mode, and there is pixel phenomenon in the projected image.
LCD flat panel projectors can be divided into single-chip projectors and three-chip projectors. Modern LCD panel projectors mostly use three-piece LCD panels (Figure 1). The three-piece LCD projector uses three LCD panels: red, green and blue, which are used as the control layers of red, green and blue light respectively.
The three-piece LCD projector has higher image quality and brightness than the single-piece LCD projector. The LCD projector has the advantages of small size, light weight, simple manufacturing process, high brightness and contrast, and moderate resolution. It is the most widely used projector in the market at present.
Figure 1 Working principle of three-piece LCD projector
B. liquid crystal light valve projector
The liquid crystal light valve projector uses CRT and liquid crystal light valve as imaging devices, which is the product of the combination of CRT projector and liquid crystal light valve. It is the projector with the highest brightness and resolution so far, with brightness of 6000ANSI lumens and resolution of 2500×2000. It is suitable for occasions with light intensity and large audience, such as super-large command center, conference center and large entertainment places, but the light valve is expensive, bulky and difficult to maintain. The main brands are: Hughes -JVC, Ampro and so on.
3.DLP (Digital Light Output of Digital Light Processor) digital projector
DLP technology is a patented technology of TI (Texas Instruments). The projector based on DLP display technology first appeared in 1996. Its imaging device is DMD (digital micromirror device). DMD chip contains thousands of micromirrors, each mirror represents a pixel, and the on or off state represents the brightness of the pixel in the image. The light beam is projected onto the DMD through the high-speed rotating color wheel (color separation device), and then onto the big screen through the optical lens. At present, DLP technology is patented by TI, and TI is also the only supplier of DMD chips.
First, the technical advantages of DLP projectors
The first is digital advantage: the adoption of digital technology makes the contrast, gray scale (256- 1024), color (2563- 10243), signal-to-noise ratio and stable image quality of the image excellent.
Secondly, the advantage of reflection: due to the application of reflective DMD devices, the distance between micromirrors that constitute DLP image pixels is very small, which makes the light transmission efficiency of imaging devices reach more than 85%. The generated image is very bright and has high definition.
B, DLP projector can be divided into:
Single-chip microcomputer: The advantages of single-chip DLP projector are high light efficiency, high contrast and clear image, especially in black and white graphics and text. At the same time, the single-chip DLP projector can be small and light, but the disadvantage is that the color performance is not realistic and natural.
Three-chip machine: DLP projector made of three DMD chips has higher brightness and richer colors, and the brightness can be as high as 10000ANSI lumens, which is mostly used in special occasions such as digital cinemas.
At present, projectors on the market mainly include LCD technology and DLP technology. Most Japanese manufacturers adopt LCD technology, while European and American manufacturers can adopt LCD and DLP technology. The competition between LCD and DLP is fierce. There is no clear answer about whose product and technology are better, but it can be said for sure that the projector using DLP has higher picture contrast and more compact optical system, so it has advantages in volume and weight. And LCD is very strong in brightness uniformity, color and detail. The two technologies have their own characteristics and are inseparable. They will exist for a long time to come. Unless one party makes a breakthrough in technology or market strategy, it is expected to break this balance and occupy a dominant position.