SDI Development History

In 1982, the former International Radio Advisory Committee (CCIR), based on the agency proposals of the European Broadcasting Union (EBU) and the American Society of Motion Picture and Television Engineers (SMPTE), issued CCIR Recommendation 601, which unifies the digitization parameters of two television scanning systems, 525/60 and 625/50, using a sampling frequency of 13.5 MHz, 8-bit quantization, and 4:2:2 chromaticity subsampling. In 1986, CCIR released the CCIR 656 proposal based on the EBU Tech.3246 and SMPTE 125 standards, proposing a parallel interface that can transmit CCIR 601 specification signals, using 11 pairs of twisted pairs and 25 pin D-type connectors. Some early digital devices used this interface, but due to short transmission distances and complex connections, it is not suitable for large-scale use. In fact, CCIR 656 also includes the EBU Tech.3247 serial digital interface standard proposed by EBU in 1983, which uses 8/9 block coding and a bit rate of 243 Mb/s. However, it only supports 8-bit quantization, and it is not easy to design stable and inexpensive interface chips.
In 1983, CCIR became the International Telecommunication Union's Department of Radio Communications (ITU-R). In 1994, ITU-R released the BT.656-2 Recommendation, incorporating the new serial digital interface defined in EBU Tech.3267 and SMPTE 259M, which uses 10 bit transmission and non return to zero reverse (NRZI) coding. When transmitting ITU-R BT.601 (Part A) 4:2:2 level signals, its clock return rate is 270 Mb/s, which is now known as SDI. The use of 75 ohm coaxial cables and 75 ohm BNC connectors (IEC 60169-8) enabled the reuse of a large number of previously laid cables within television stations in digital systems. Later, SDI gradually became the standard configuration for digital equipment, and on this basis, the digitization of the studio, master control, and broadcast control systems was finally achieved. China has also formulated the corresponding national standard BG/T 17953 with reference to the above standards. In order to meet the requirements of high-quality program production for ITU-R BT.601 (Part A) 4:4:4:4 level images and color keys, EBU Tech.3268, SMPTE RP145, and ITU-R BT. 799 have proposed the concept of dual links, that is, transmitting R'G'B '/4:4:4 images and another broadband signal through two SDI channels simultaneously. The corresponding industry standard formulated by the State Administration of Radio, Film and Television of China with reference to ITU-R BT.799-3 is GY/T 159-2000. In addition, the SMPTE 344M also defines a serial digital interface with a clock frequency of 540 Mb/s.
In 1990, the ITU-R BT.709 proposal was issued, and the development of high-definition television technology accelerated. The adoption of serial digital interfaces to transmit high-definition signals has reached consensus in the industry. Therefore, SMPTE defined a clock frequency of up to 1. 5% in the 292M standard The serial digital interface at the 5 Gb/s level corresponds to the international standard ITU-R BT. 1120. GY/T 157-2000 is an industry standard formulated by China according to the ITU Recommendation, which is known as HD-SDI. In addition to increasing the clock frequency to 5.5 times 270 Mb/s, or 1.485 Gb/s, there are also some differences between HD-SDI and SDI. For example, HD-SDI places brightness and color difference signals in two streams, multiplexes them, scrambles them, and transmits them. The encoded line number and check code are attached to the end of active video (EAV). Due to the use of 75 ohm cables and connectors, as well as the successful experience of SDI, HD-SDI quickly replaced the parallel interface previously used. Similar to SDI, SMPTE has standardized dual link HD-SDI in the 372M standard to meet the transmission of content in the 1080p50/59.94 format in studios. Advances in high-speed interface chip technology have made the 3 Gb/s level serial interface possible.
In 2005, ITU-R provided specifications for a 2.97 Gb/s serial interface in the BT.1120-6 proposal. The physical media still uses 75 ohm coaxial cables and IEC 60169-8 standard connectors. In addition, SMPTE 424M also provides a similar definition of a 3 Gb/s level interface. The emergence of a 3 Gb/s serial interface has solved previous situations where dual link HD-SDI was required, such as 4:4:4/12bit or 1080p50/59.94 format program production. Manufacturers have announced the launch of 3 Gb/s serial interface chip products. In some situations where long-distance transmission is required, such as connecting two distant studios, copper cable becomes somewhat inadequate, and optical cable naturally becomes a substitute for copper cable. ITU-R BT.1367, SMPTE 297M, and GY/T 164-2000 in China are all standards that use optical cables to transmit serial digital signals. Taking ITU-R BT.1367 as an example, when transmitting high-definition signals, only single mode optical fibers and corresponding optical connectors are allowed, and the optical electrical and electrical optical conversion is completed by corresponding optical receivers and transmitters. Emerging digital movies have higher definition images, higher resolution, and richer colors (e.g. SMPTE 428-1K PGYQR 4096 × 2160 4：4：4/X’Y’Z’/ 12-bit@24P ）"The amount of data that needs to be transmitted between digital movie devices (such as digital projectors and servers) is greater. Therefore, SMPTE N26 Technical Committee is developing the 435M series standard - a serial data interface with a clock frequency of 10.692 Gb/s, and its physical medium is an optical cable that conforms to the IEC 60793-2 standard and an optical connector that conforms to the IEC 61754-20 standard.". This 10 Gb/s level interface can multiplex up to eight HD-SDI data streams together, or map existing 1.5 Gb/s and 3 Gb/s data structures onto a 10 Gb/s interface.