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What is SDI ?
Pertenecer a la categoría: Noticias de la compañía
Fecha de lanzamiento: 2023-06-01
Tarifa de clics: 560
El editor: yuxun
In this section, we will explain everything from an overview of the SDI standard to points to note when designing boards for those who are new to SDI interfaces.

In this section, we will explain everything from an overview of the SDI standard to points to note when designing boards for those who are new to SDI interfaces. At the end of the article, we have listed the recommended products of Yuxun company, so we hope that it will be useful for your design.

What's SDI ?

When asked about an interface that can transmit video signals, we think of HDMI, which is widely used in digital home appliances. Some PCs use DisplayPort, and recently there are more and more cases where video signals are transmitted via USB Type-C. The distance that can be transmitted in HDMI and DisplayPort is limited to about 5m. Uncompressed video can be transmitted over long distances using fiber optic cables or using SDI. SDI is a technology with a long history in the world of broadcasting stations and TV relays, and it realizes signal transmission over tens to hundreds of meters.

SDI is an abbreviation for Serial Digital Interface , and is an interface mainly used in the broadcasting and video industries . To explain it in a little more detail, it is a standard defined by SMPTE (Society of Motion Picture and Television Engineers: American Society of Motion Picture and Television Engineers) and is an interface that can transmit uncompressed digital video signals over a single coaxial cable. As an advantage for the user, in addition to being able to connect with a single cable, the use of a BNC connector with a locking mechanism that does not require the use of screws means that there is a locking mechanism that prevents the cable from accidentally falling out. (If the cable is pulled out during the TV relay, it will be a broadcast accident). Compared to HDMI, HDMI does not have a locking mechanism in the connector, and requires a total of 8 cables, 3 differential pairs of data lines and 1 pair of clock lines. The biggest difference is the transmission distance, which is several meters with HDMI, but can be several tens to hundreds of meters with SDI. In order to connect the studio in the broadcasting station to the remote editing room, about 100m is necessary. Optical fiber cable exceeds SDI in terms of transmission distance, but SDI is superior in terms of usability, power consumption, and cost.

About the SDI standard

With SDI, however, new standards have been established in line with recent advances in image quality and resolution, and the data rate of SDI has also become faster. The following shows the relationship between SDI standard model name, image quality/resolution and data rate.

SD-SDI, SDTV quality (e.g. NTSC/PAL), 270Mbps

HD-SDI, HDTV quality (e.g. 1080i59.94, 720p59.94), 1.485Gbps / 1.4835Gbps

3G-SDI, Progressive HD (e.g. 1080p59.94), 2.97Gbps / 2.967Gbps

6G-SDI, 4K resolution (e.g. 4K 29.97p), 5.94Gbps / 5.934Gbps

12G-SDI, 4K resolution (e.g. 4K 59.94p), 11.88Gbps / 11.868Gbps


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Since SDI achieves long-distance transmission, coaxial cables with an outer diameter of about 1 cm are generally used. Depending on the cable type, this allows transmission over SD: 500m, HD: 200m, 3G: 100m, 12G: 70m or more. Figures 1 and 2 are SDI cables manufactured by Zhuhai Yuxun Company . Transmission characteristics are 1.5 times better than conventional 5C-FB cables, and 100m transmission is possible with 12G-SDI.

I explained that SDI uses coaxial cables like the one above, but they use coaxial cables with a characteristic impedance of 75Ω, similar to those used in broadcast antennas. The use of 75Ω coaxial cable has a historical background. At the beginning of coaxial cable development, "air" was used as the insulator of the cable, and as a result of optimizing the performance with the structure, it became a characteristic impedance of "75Ω". Currently, the insulation material has changed from air to polyethylene, etc., and the characteristic impedance of cables is generally 50Ω.

However, SDI inherited the above history as it is, and even today, the world of transmission lines is 75Ω. On the other hand, differential 100Ω interfaces such as LVDS, CML, and LVPECL are common for input/output of high-speed ICs. In order to bridge the differential 100Ω world and the 75Ω single-ended world, SDI uses a dedicated IC called a "Cable Driver" on the transmitting side and an "Adaptive Cable Equalizer" on the receiving side. In recent years, SDI over IP (IP transmission) using optical interfaces based on SMPTE ST-2022 (AIMS/ASPEN/NMI, etc.) and SMPTE ST-2110 standards is increasing. However, broadcasting stations are expected to continue to adopt SDI because of the need to completely refurbish the facilities in their buildings and the cost of fully introducing SDI.

Summary

As mentioned in this article,SDI is expected to continue to be used as a video transmission cable, although its specifications are changing. Next time, I would like to tell you about the SDI standard and layout design .

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