Designing a next-generation video interface with thunderbolt technology

Tam Do, Pericom
EDN (August 6, 2013)

With today’s high definition (HD) video and the upcoming 4K ultra-high definition standard, more bandwidth is needed to transport video data between sources (i.e., cameras, storage) and sinks (displays, storage) in video production environments. The traditional method for bringing those data out consists of a USB interface for data and either DisplayPort or HDMI for video output. With the introduction of the Thunderbolt interface, a system interface can be simplified with one connector for both data and video.

The amount and speed rate of data are ever increasing as video resolution moves from high definition to ultra high definition. For example, a 4K video with 4096 x 2160 pixel resolution, color mode of RGB 444, and 12-bit color has a raw, uncompressed bit rate of 19.11Gbps or 2.39GBps. This is just for one frame of video. Storing 30 seconds of such video requires 71.66GB of disk space.

USB 3.0 is one connectivity option for video interfacing. However, this would introduce significant latency when a user is editing in real-time using video stored on a hard disk. The main reason for this is that even with its data rate of 5 Gbps, USB’s unique command set was not designed for handling real-time video transport. In addition, the latency gets worse when more USB devices are daisy-chained together.

The Thunderbolt interface, with its 10Gbps data rate, allows architectural designs to achieve the speed, minimal time latency, and storage capabilities required for real-time video studio production. Professional studio and broadcast video equipment can make use of this technology in video capture cards, storage devices, adaptors, and video displays. Furthermore, devices can be daisy-chained up to a maximum of 6 devices using Thunderbolt cables without significant data overhead reduction compared to other serial protocols.

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