This article refers to the address: http:// With the continuous improvement of image display quality requirements, the traditional technology of transmitting and displaying multimedia signals in analog mode can no longer meet people's requirements. The implementation of digital conversion and digital TV in the broadcasting and television industry, digitalization, networking, Fiber optics is a trend in the IT industry. The application of consumer digital video equipment represented by high-definition digital TV is becoming more and more popular. The traditional analog video interface standard cannot adapt to the development needs of new products in terms of bandwidth, content protection, audio support, etc., making HDMI, UDI and DisplayPort The new standard seems to be more adaptable to the needs of the market. This article starts with the traditional analog video interface, briefly introduces several digital video interface technologies and standards, and focuses on two digital video interfaces, HDMI and DisplayPort. Development of analog video interfaces DVI, HDMI and UDI standards and applications Figure 1 Single-link TMDS connection diagram Figure 2 Schematic diagram of the basic structure transmission of the DVI/HDMI/UDI transmitting and receiving system (TMDS) Figure 3 Transport layer architecture of the DisplayPort interface to sum up Custom Keyboard Cables,Custom PC Cables,Custom Automotive Harness,Custom Industrial Cable Dong guan Sum Wai Electronic Co,. Ltd. , https://www.sw-cables.com
In China, the simplest, most primitive and most widely used video interface is the composite video signal (CVBS, A/V) interface, which is commonly referred to as the RCA interface, along with S-VHS camcorders, VCD and other laser disc products. An S-terminal (Y/C, S-Video) interface that separates the luminance signal Y from the chrominance signal C has appeared, along with an analog component video signal (Y, U, V, or with a DVD, satellite digital television set-top box (IRD). Y, RY, BY) interface; in the field of PC communication, the general interface D-SUB (9-core) port, also known as the VGA terminal, has appeared.
1 DVI standard
DVI is called Digital Visual Interface. It is a non-compressed real-time video interface standard for the connection between PC and VGA monitors, which was launched by the Digital Display Working Group (DDWG) in April 1999. It transmits digital signals based on TMDS (Minimized Transmission Differential Signaling) technology, as shown in Figure 1.
The TMDS consists of three RGB data and one clock, a total of four channels (called a TMDS connection or a single-link) transmission loop. TMDS converts 8-bit RGB video data into 10-bit conversion minimized, DC balanced data, and then serializes the data; the receiving device de-serializes the serial data into parallel data, and then converts it into 8 bits. Video signal. Therefore, transferring digital RGB data requires three conversions to minimize the differential sampling signal to form a TMDS connection. Each channel provides 165MHz bandwidth, a 10-bit TMDS transmission channel rate of 1.65Gb/s, and 3 TMDS channel rates of 4.95Gb/s. If dual-1ink connection is used, its bandwidth can reach 330MHz, the transmission rate can reach 9.9Gb/s, support 1600×1200@85Hz UXGA or 2048×1536@75Hz QXGA image and 720p, 1080i, 1080p HDTV video signal. Uncompressed real-time transmission.
Due to the large size of the connector, DVI is not compatible with audio signals, and the transmission distance is only 5~7m. It is replaced by HDMI interface. DVI 1.0 and later versions are basically no longer developed.
2 HDMI standard
In April 2002, the HDMI (High Definition Multimedia Interface) working group developed the HDMI (High Definition Multimedia Interface) standard, which improved the shortcomings of the DVI standard. Figure 2 shows the HDMI schematic.
HDMI is an upgraded and enhanced version of the DVI standard that supports audio signals and can be easily understood as: DVI+Audio=HDMI. The HDMI interface is compact (comparable to USB), the cable length is 15m, HDMI is backward compatible with DVI; HDMI supports HDCP (High-bandwidth Digital Content Protection) organized by VESA to avoid illegal copying of content, and also supports EDIA of the VESA organization. Display identification data), DDC (display data channel for reading EDID) and DMT (monitor synchronization protocol).
HDMI also uses TMDS encoding. TMDS has RGB or YPbPr color data and clock, a total of 4 channels (called 1 connection) series transmission loop, 1 channel bandwidth 165MHz (4.95 Gb / s). The display data channel (DDC) is a signal line for reading extended display identification data (EDID) indicating display capability such as reception side resolution. The DDC line is also used to authenticate the cryptographic keys between the transmitting and receiving devices equipped with HDCP. This is an encryption system using a hardware ID, and the transmitting side and the receiving side mutually confirm each other for transmission at a certain interval. HDMI is equipped with powerful content protection technology that immediately interrupts the transmission of image and audio signals when authentication is not established or is not established midway.
As can be seen from FIG. 2, the transmitter separately converts and synthesizes the video and audio signals into a signal format that the receiver can receive. Then, HDCP encryption processing and TMDS encoding are performed, and parallel data lines such as video and audio are serialized to be transmitted in a form of minimizing differential signals. The processing performed on the receiving side is reverse to the order of the transmitting side.
The previous version of HDMI 1.3 has a single-connect channel bandwidth of 165MHz (4.95Gb/s), which is the same as DVI, but can transmit 1 to 8 sets of uncompressed audio, and supports multiple sampling audio frequencies such as 48/96/192kHz. In order to adapt to the development of technology and market demand, the latest version of the HDMI1.3 standard was released in June 2006, which has high transmission bandwidth (10.2 Gb/s), "Deep Color" and "xvYCC" colors. With powerful features, as video resolution evolves from standard definition to high definition, the increasing video bandwidth will be the trend, and more electronic products with HDMI 1.3 interface will appear. There is no doubt that HDMI 1.3 will usher in the peak of its application in 2007. HDMI 1.3 has the following new features.
â— Broader bandwidth (higher speed): HDMI 1.3 increases its single bandwidth from 165MHz (4.95Gb/s) to 340MHz (10.2Gb/s), fully supporting the needs of high-definition display devices.
â— Dark: Supports 30-bit, 36-bit, and 48-bit (RGB or YCbCr) color depths. The color depth of the HDMI specification version before 1.3 is up to 24 bits.
â— wider color space: HDMI 1.3 completely removes all the limitations of color selection: the next-generation "xvYCC" color space is 1.8 times that of existing HDTV signals; making HDTV display colors more accurate; making the display's colors more natural and realistic.
â— New mini interface: HDMI 1.3 offers new and smaller form factor interface options as small portable devices such as HD camcorders and digital cameras require seamless HDTV connectivity.
â— Lip Synchronization: HDMI 1.3 adds automatic audio and video synchronization, enabling the device to automatically and accurately synchronize the lip sound.
â— New lossless audio format: In addition to HDMI's support for high-bandwidth uncompressed digital audio and the existing performance of all existing compression formats, HDMI 1.3 also adds new lossless compressed digital audio formats to Dolby True HD and DTS-HD Master. Audio support.
3 UDI standard
UDI (Unified Display Interface), a unified display interface, is a digital display interface standard for PCs compatible with high-definition television signals. UDI Revision 1.0a, which was developed by the SIG (Special Interest Group) in July 2006, was officially announced. . The TMDS encoding technology and content protection mechanism adopted by UDI are the same as DVI and HDMI, and are compatible with DVI and HDMI interfaces. Currently, the interface standard using TMDS technology has reached a three-pronged trend. One data channel can transmit up to 2.7Gb/s, three channels have 8.1Gb/s transmission rate, and the RGB format can be up to 12-bit 36-bit color full HD (1920×1080 pixels, 60 frames) / sec) Video signal transmission. UDI, like DVI, does not support audio signal data transmission. UDI does not require a royalty fee, but the initial license fee is payable.
4 DVI, HDMI, UDI simple comparison and application prospects
UDI and DVI do not support audio transmission. UDI has a slightly higher bandwidth than DVI. It is regarded by the PC industry as a follow-up standard for DVI, and is mainly applied to the video display interface of PC. HDMI supports audio signals and luminance color difference signals (YPbPr), which can be applied not only to video display interfaces, but also to high-speed multimedia interfaces for Consumer Electronics, such as high-definition DVD players, digital TV set-top boxes, LCD, DLP, PDP, HD CRT. Connect to large-screen high-definition display devices to build next-generation home theaters with high-definition TV images and multi-channel audio.
DisplayPort standard and application prospects
In May 2006, VESA (Video Electronics Standards Association) approved the DisplayPort 1.0 display interface standard for PCs, monitors, televisions, and projectors. DisplayPort (referred to as DP) is mainly composed of main link, auxiliary channel and hot plug signal detection (HPD), as shown in Figure 3. The primary link is a high-bandwidth, low-latency one-way transmission link for transmitting uncompressed video and audio streams. The auxiliary channel is a 1Mb/s bandwidth, low-latency bidirectional channel for transmitting status information and control. Commands, etc., and provide primary link management and device control; hot-plug signals implement Sink Device interrupt requests.
The main link consists of 4 lines (Lane), each supporting 2.7Gb/s or 1.62Gb/s transmission rate, 4 can achieve 10.8Gb/s, and DisplayPort is 2.2 times faster than DVI under the same number of lines. . Therefore, DisplayPort can meet the needs of various multimedia, especially video applications. Any color depth (Phase Depth), resolution and picture refresh rate (Rate) can be freely converted. DisplayPort does not have a separate clock channel. The main link uses ANXI 8B/10B encoding, and the clock signal is extracted from the data stream. This difference from DVI and HDMI features greatly reduces the difficulty of EMI design for DisplayPort products. The auxiliary channel is a two-way, half-duplex channel consisting of a pair of AC-coupled differential lines. All communication must be initiated by the source device, and the terminal device can also initiate a communication request by hot-plugging the signal. The auxiliary channel provides a transmission rate of 1 Mb/s over a transmission distance of 15 m, which requires strict transmission delay and communication must be completed within 500 μs. Because of the hot plug signal detection, it supports the plug-and-play and hot-swap functions of the device.
In addition to the high bandwidth advantage, DisplayPort has the following advantages.
â— Micro-Packet Architecture architecture transmission: On the primary link, all video and audio data streams are packed into micro-packets (composed of 64 codes). At the same time, the micro-packet architecture can transmit multiple sets of video in the same line, while the switched transmissions used by DVI, HDMI, and UDI limit a link to transmit only one set of video. In addition, this architecture makes it easy to add new protocol content to existing transports, such as content copy-protection agreements.
â— DPCP, DP content anti-copy protection: micro-packet architecture can flexibly add transmission protocol, DPCP adopts improved new anti-copy protection mechanism, utilizes AES-type high-speed 128-bit content encryption, and does not use 40-bit secret used in HDCP specification. key.
â— DisplayPort is an open digital display interface standard that can reduce the cost of equipment without patent fees.
Based on the DisplayPort main link, it can transmit uncompressed video streams with audio. Its scalability supports multiple video or audio streams. It also provides 1Mb/s, low latency and bidirectional auxiliary channels, suitable for interactive, dialogue and other applications. Support plug-and-play, can support HDTV, video and other protected content, not only can replace DVI / HDMI, but also replace LVDS, the application prospect is very broad.
DisplayPort's transmission rate, security, openness, and scalability are obvious advantages over other video interfaces. It is an ideal digital multimedia interface that meets the requirements of digital multimedia interfaces in the PC and consumer electronics fields. However, DisplayPort is not compatible with DVI, HDMI, and UDI. The application prospect of DP needs to be tested by the market. HDMI is based on DVI and can transmit digital audio signals. It is also an excellent interface for consumer electronics. HDMI is developing rapidly and is gradually replacing DVI. UDI and DisplayPort have the same goal in PC applications because they do not require a patent fee: external replacement VGA, internal replacement LVDS. The comparison between them is shown in Table 1.