With the large screen projection display technology development, especially digital LCD, DLP and PDP plasma and other digital products and the extensive application of digital signal standard uniform, the traditional VGA analog signals can no longer satisfy the needs of the development, a growing number of DVI ( Digital Visual Interface) signals HDCP (High-bandwidth Digital Content Protection High-bandwidth digital content protection) signals and HDMI (High Definition Multimedia Interface) digital signal, and so widely used. This paper features on the digital signal itself, the current application status, the current technical difficulties and development prospects to do a brief introduction.
A. Digital signal itself Features
DVI signals, HDCP signal and HDMI signal for VGA signal, if eliminating all kinds of agreement, essentially the same signal channel, all DVI signal. So first introduced DVI signal characteristics.
The simulation shows that way, the figures will be displayed RGB signal (8 bit parallel signals) cards in the D/A converted into analog signals, transmission and entered monitors, treated drive RGB electron gun, displayed on the screen, the entire the process is simulated. The figures show that different ways, analog RGB signal after reaching the display device (LCD or DLP, PDP, etc.) After A/D processing, conversion to digital signals, then controlled by the digital signal transmission or reflective LCD panels or DMD chip reflection of light Luminescence light or plasma, to show results. In this process by clearly there is a digital simulation ★ ★ digital conversion process, signal loss larger (one A/D, D/A process will be a loss 6 dB frequency bandwidth reserved for the largest pixel clock 1/2 ), and there will be such as smearing and blurring, ghosting, and other transmission problems. Current digital interface with the computer graphics has been very common, and even notebook computers are equipped with a DVI interface, display equipment is also an increasing number of equipment with digital signal interface, digital ★ digital system, the environment is ripe .
DVI principle is to be displayed on the RGB signal and digital signal combinations HV coding, each pixel by 10-bit digital signal by the smallest non-RZ coding manner and ★ string conversion to RGB digital encoding the serial code , was equivalent to 0.7 GHZ. General DVI1.0 the bitstream at 0.24 GHz to 1.65 GHz between.
DVI interface defined as follows Banner:
DVI has DVI1.0 and DVI2.0 two standards, which DVI1.0 took only one of a group of signal transmission channel, the maximum transmission image pixel clock is 165 M (1600X1200X60, UXGA), the maximum signal transmission channel code Flow of 1.65 GHz. DVI2.0 then spent all of the two groups of signal transmission channel, the maximum transmission image pixel clock for 330 M each of the maximum signal transmission channel bit stream for the 1.65 GHz. In the large-screen display devices, has not DVI2.0 the application of this paper are discussed DVI means DVI1.0 standards.
DVI definition of a DVI-I (Integrated), and DVI-D (Digital) interface, interface definitions, we can see that the DVI-I is in fact DVI-D on the basis of an increase of analog interfaces. We are introduced DVI-D interface.
HDCP signal from the interface forms, pin definitions, data formats, and so the same with DVI is considered confidential reasons, the data are encrypted to comply with the requirements of the agreement HDCP. This is just taking into account different levels of agreement, we can consider this equate the two.
HDMI's English name is "High Definition Multimedia Interface," which not only high-definition multimedia interface. HDMI interface can provide up to 5 Gbps data transmission bandwidth can be transmitted uncompressed digital audio signal and high-resolution video signal. HDMI and DVI in pin-compatible, but use a different package, can be considered the strengthening and extension of DVI, the two can be compatible. Compared with DVI, HDMI can transfer digital audio signal, and to increase the support for HDCP. A 1080p video and an 8-channel audio signal demand is less than 4 GB/s, so there is a great cushion HDMI. In addition HDMI support EDID (extended display identification data - Extended display identification Data), DDC (Display Data Channel - Data display channel to read out EDID), HDMI equipment with "plug-and-play" features, signal source and the display device will automatically between a "consultation", automatically selecting the most suitable video/audio formats. HDMI support RGB signals, 4:4:4 sampling YCbCr signal and 4:2:2 sampling YCbCr. Maximum transmission rate of 24/pixel. HDMI audio data formats: DVD-based audio standard, non-HDMI support 1-8 Group compressed audio transmission, audio support 48,96 or 192 kHz sampling rate, and other. According video formats, HDMI can be different number of transmission in the 192 kHz sampling rate for compressed audio.
HDMI interface characteristics:
A transmission cable to meet the needs of video and audio signals, all the HD signal and audio signal with a cable in the transmission, including five video and multi-channel audio components.
HDMI interface also supports the transmission of information such as the aspect ratio and intelligent signal formats, such as control information for the intelligent control equipment may be provided.
Support HDTV 1080P and higher definition signal transmission and display, adapt HDTV applications. Support DVI1.0 standards, to UXGA resolution. It that the HDCP compatible HDMI and DVI.
DVI: Digital VGA signal only
HDCP: DVI signal than increased confidentiality agreement
HDMI: VGA, DVI compatible, HDCP, to UXGA resolution. Video, and the next support 1080 P compatible. Audio support all the different types of digital audio.
In 2005, already have more than 250 vendors and 470 different types of products using the HDMI interface. DVD Copy Control Association (CCA), the United States of FCC (Federal Communications Commission), on behalf of the European information and communications technology and consumer electronics industry organizations such as the Organization EICTA provide all the high-definition digital television equipment (HD-STBs) must have HDMI -- HDCP or DVI-HDCP output terminals, computer graphics will also HDMI as standard interfaces. All these provisions are strengthened more HDMI position in the market. HDMI has become the de facto digital TV and consumer electronics products interface standards.
B. Application of Digital Signal advantage
With remarkable control signal display device works in the development of the projector's increasingly high-resolution and brightness of the signal higher and higher demands, and traditional analog transmission and application of the signal system in large losses, resulting in high-quality the projection equipment not display high-quality images, a display quality bottleneck. Digital transmission systems and simulation and application of the technology systems have a distinct advantage compared to:
1. Reduction of analog/digital (A/D), D/(D/A) conversion process. VGA signal in the course of the show, the notebook is the highest quality image, the CPU will be displayed to the data card, a card to be processed and displayed graphics signal (8 bit parallel digital signal) directly drive LCD screen, forming the notebooks show that this is the most "original" signal processing and without any loss. Will graphics signal (digital) through D/A converter, a RGBHV (VGA) signals, the signals at this time, after D/A conversion, causing as bandwidth, such as the loss of SNR. Transmission equipment also showed that arrived after A/D process, re-generation digital signal, driving LCD equipment has also caused A/D process losses. Will graphics signal (digital) process and/string transformations, DVI signal, without loss through DVI transmission equipment arrived, and only then revealed that the string/and conversion, can directly drive LCD and other equipment, the process did not After A/D, D/A process, and no report of loss of signal.
2. Reduction of signal transmission loss in the process. Previously, article analysis, analog signal transmission, because the amplitude-frequency transmission system holders and holders of group delay, high low frequency interference, power ground wire interference and reflection effects, signal serious damage in resolving and dealing with the works above it is very difficult issues, some even insurmountable. But digital signals would not have this problem, the biggest advantage of digital transmission interference capability and the reconstruction could be renewable, briefly, is guaranteed as long as the transmission process, "0", "1" no wrong, or the signal is - correct and nondestructive, analog transmission in many difficult problems in the transmission of digital process does not exist in this "concept" is a fundamental solution, can guarantee that the signal reached projection equipment and notebook screen as a signal can full play the advantages of the display device, the whole system has markedly enhanced the quality of the display.
Because no need to send signals before the D/A or A/D and can ensure the highest quality audio and video signal transmission.
3. Conducive to the unity of the signal system. HDMI technology is digital video (Video) signals, audio (Audio) VGA signal and the three combined for the same signal interface to the same standard coverage to address the original different signals and different interface, caused by different standards Application inconvenience. In the past, engineering design, there is a video, audio, and VGA signal, and sometimes also DVI signals, signals are not unified, transmission channels are not unified, not unified interface, choose equipment not unified, works in a great trouble. Application of the three signals to the respective design and consider, from the selection of equipment, cable choices, there might be a different type of interference, attenuation, the word, we should consider three issues. But after the application of digital methods can be combined for the three issues a problem, it may only a uniform equipment to resolve all the problems. Just think, the future of a day, in engineering applications do not have to consider the number of video road, how much of the selection matrix, no need to consider a few road audio, how to use audio equipment, the number of VGA signal transmission to how far what will be the interference, attenuation, and so on. Just consider the number of single road HDMI signal (its transmission distance is the standard available), just consider how far from the election with network or cable transmission line cost-effective, or using fiber better. Equipment will be displayed as long as the received signal equipment HDMI interface on OK. Home applications to achieve this step easier, television (particularly flat-screen TVs) has a HDMI interface, only "fool" on a trip then. But not so fast engineering application, or to gradually move toward digital applications.
C. The current level of technology and equipment and the main problem
1. Digital Matrix smaller scale. Beijing Liguo companies in the world were the first to launch 8x8, 16x16 digital matrix, the current international level will be the case. 18 x18 matrix reports. Expected this year, Beijing Liguo companies will come in 32 x32 digital matrix. Speaking from the actual project needs, the digital matrix scale is still small, large-scale systems application problems.
2. Transmission to basically solve the problems. In addition to transmission cables, network transmission and optical transmission line equipment had matured, and in the large-scale application of practical engineering. Major domestic or more ways to use cable, fiber optic equipment also have application, but we have a large number of products export network, the network is expected to domestic digital transmission lines will be followed.
3. Conversion. After the emergence of new media, in addition to its own application, there also exists with the traditional media conversion. Currently, between DVI and VGA signal conversion equipment has been very mature to meet the application requirements. Video, HDMI similar to the SDI conversion can be completed, but because the HDMI issue of security, would not allow the HDMI signal solutions into codes, HDMI signal to other types of technical barriers, limits the application.
4. Currently, the high cost of entry HDMI technology, the only entry for the annual fee on US $ 15000, HDCP annual fee for US $ 15,000, and sales of products still need to pay each US $ 0.0 5 to US $ 0.15 in royalties, HDMI compatibility testing fees from US $ 11,000 starting to US $ 50,000, US $ 80,000 also normal, and time is very long. Really so-called "black is the most standards," Will a future DVD-style patent dispute is not known. Current PC manufacturers a little HDMI graphics, and related estimates.
Current digital, high-definition digital status should be:
1. Technologically advanced, easy-to-use, broad application prospects
2. The current costs are relatively high, but declining very rapidly, and even cheaper than analog mode.
3. Projects, the DVI approach may be applied more quickly, but HDMI will be more flexible than DVI.
4. Technical level, the domestic unlike foreign worse than some foreign development faster, at least at the same starting line.
5. A certain degree of technical difficulty and technical barriers, entry costs are relatively high.
In 2007 Beijing INFOCOMM Exhibition, in addition to Beijing Liguo companies display traditional audio and video, VGA equipment, but also displayed a new digital DVI, HDCP, the full range of HDMI products, including: switching, distribution, conversion, transmission category equipment, their equipment has been leading the world's advanced level.