Moving Digital Broadcast Into the 21st Century
By Vasilis Papanikolaou, Manager, Gennum Corporation
It’s not your mom and dad’s TV anymore…or is it? Just as TV has evolved from The Brady Bunch to The Cosby Show and finally into Wife Swap, digital broadcast formats are also evolving.
Vasilis Papanikolaou, Manager, Gennum Corporation
By Vasilis Papanikolaou, Manager, Gennum Corporation
It’s not your mom and dad’s TV anymore…or is it? Just as TV has evolved from The Brady Bunch to The Cosby Show and finally into Wife Swap, digital broadcast formats are also evolving.
Seventy years ago video signals were analog based, distributed on 75 Ω coaxial cables and terminated with BNC connectors. Gradually, in the 80s, the industry transitioned to serial digital interfaces (SDI) (SMPTE 259M), but retained the 75 Ω coaxial infrastructure.
The future has arrived, but only in its desire to retain our old friend coaxial, while pushing toward high-speed interfaces supporting 2.97 Gbit/second serial digital transfer. If there’s one thing our parents and grandparents taught us, it’s “Where there’s a will, there’s a way.” In order for the broadcast industry to satisfy the bandwidth requirements of multiple HDTV formats (720p/50 and 1080i/50) and video formats for digital cinema, they will need higher-speed SDI interfaces, without the expense of rewiring through building walls and conduits.
New standards for a 2.97-Gbit/sec SDI interface using 75 Ω coax cable and BNC connectors have now been adopted by both SMPTE (SMPTE 424M and 425M) and the ITU (ITU-R-BT.1120-3-2005). Semiconductor devices are commercially available to enable a 2.97-Gbit/sec SDI interface using the existing cable infrastructure. But are they technically and economically feasible? Absolutely.
Gennum Corporation, a pioneer in authoring SMPTE 424M and SMPTE425M, as well as delivering a 3Gb/s SDI-compliant products, has solved some of the key issues in moving from HD-SDI to 3 Gb/s-SDI – a move that doubles the data rate. Click here for more information. 3G video.
Implementing three chips, the solution solves the problems that can occur when sending this high-speed signal across copper cable.
One of the limiting factors for sending high-speed signal over copper cables is the skin effect, which causes increased attenuation as the frequency of the signal increases. The skin effect causes insertion loss which increases as the square root of the frequency of the signal it carries. To solve this problem, solutions implement an equalizer which acts as a filter with a frequency response that is the complement of the response of a cable.
But probably the biggest challenge is reducing jitter. In fact, the absolute jitter (in ps) needs to be cut in half in order to keep the same amount of Unit Interval (UI) jitter. Gennum implements a data-reclocking circuit to reduce jitter in 3 Gb/s SDI designs.
So as TV gets more real with ever-evolving high-definition standards, know that we have made the most of the foundation built by those who went before us. We will continue to move forward, without leaving our copper friend behind.
About the author:
Vasilis Papanikolaou is currently the manager of video transport product marketing. He has been with Gennum since 1999 working as an IC designer and an IC design manager for Gennum’s Transport & Timing products, where he created a number of patent related to high speed serial interfaces. He holds bachelor’s and master’s degrees in electrical engineering from the University of Toronto and is a senior member of the IEEE. Vasilis also acts as the Chair of the IEEE SSCS for the Toronto Section.
Click here for details on the Gennum product family: www.gennum.com
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