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Applying advanced analog and digital techniques to long video-cable equalization

October 19, 2010 | Dave Ritter and Tamara Schmitz | 222901204
Applying advanced analog and digital techniques to long video-cable equalization Dave Ritter and Tamara Schmitz of Intersil Corp., focus on the challenge in transmitting video over distances and examine the advanced analog and digital techniques required to achieve long video-cable equalization.
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(Editors note: We also have an on-going series of dialogues between these authors; there are links to them at end of this piece, immediately above the About the Authors section. There are also two "Desert Island Design" articles, by one of the authors.)

The challenge in transmitting video over distances is to get more information down longer cables faster. The longer distance video images must travel, the longer the cable must be. As cables lengthen, resolution is lost. These losses affect any type of transmission, but they are definitely most complicated at the higher data rates required by video.

Techniques like equalization can help, but distance remains a challenge once information needs to move more than about 300 meters, or about 1,000 feet. For example, Ethernet in all its forms is only specified to go 300 feet. HDMI on an entertainment center is usually limited to a few meters unless a special cable is added. USB peripherals need to be within five meters a desktop PC to avoid losses. Security cameras, an increasingly popular and necessary application today for video, need to be within 300 meters of the console or the picture will suffer.

These distances are not long enough for larger commercial buildings, security system applications, and other innovative uses for distributing video around locations such as airports, malls and stadiums. . Video feeds in these kinds of facilities need distances much greater than in the past. Its critical to break the 300-meter barrier.

Applying advanced analog and digital techniques to the challenge of long cable equalization involves automatic sensing of video signal parameters and implementing appropriate correction and equalization.

Equalization

The circuitry used to compensate for losses in a system, called equalizers, ensures that a signal coming out of the cable is exactly the same as the signal going in. The equalizer reverses losses and makes the output signal equal to the input signal. But cable length challenges remain. The 300-meter distance is simply not long enough for the applications required today. For example, commercial buildings are larger now than ever, and video displays in airports need to reach longer distances.

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