The Shape of Things to Come?
By Dr. Eric Bogatin
www.BeTheSignal.com
July 2007
“200 million flat screen TVs are expected to be sold in the next few years,” Fred Martin, Director of R&D for the Flatwire Technologies Division of Southwire says. “The new paradigm is that the flat screen TV is on the wall and the audio, video, and game box equipment is in another corner of the room.” Who wants unsightly, bulky cables routing around your living room or family room connecting all the electronic boxes that proliferate in the home?
One solution has been wireless connectivity. But not all boxes are wireless enabled and even with information flowing wirelessly, power must still be routed. A new alternative cabling technology may enable a shift in the home entertainment equipment use model.
AC power, audio, video, and even high bandwidth data can be routed anywhere throughout a room using a cable so thin and flat that it can be painted over and disappear. “Surprisingly, builders do not pre-wire a home for the speakers and surround sound,” Martin said. “Flatwire can be concealed with paint or dry wall compound, the basic elements a painter would have. And, of course, there is always the option of under the carpet or under the wallpaper routing.” This means the possibility of invisible wiring, anywhere throughout a house, that can be installed as easily as painting or laying carpet.
Implementing AC power can be straightforward, because mechanical, installation, and safety issues dominate the features of the wire design. However, for video, data, and even high-performance speaker wire, electrical performance dominates and the design of the copper conductor patterns is critical to achieve the target performance.
“We use patterns to not only shape the signal wire but also the shielding that can be on one or both sides of the signal wires,” Martin says. For AC power, the pattern is simply two coparallel strips.
For high-performance stereo wire, an alternative is two wide strips on top of each other. This geometry offers a series inductance per length orders of magnitude below round speaker wire and a resistance not affected by skin depth until above 100 KHz, unlike round wire. Whether this electrical performance affects sound quality is a hotly debated topic among audiophiles, with just as many proponents on each side of the debate.
Video and data wire, capable of more than 100 Mbits/sec data rates is more of a challenge. Six constraints drive the pattern design:
- Manufacturability
- Thin enough for installation
- Target impedance
- Robust to radiated emissions and susceptibility
- Bandwidth
- Connector integration
The interface between the custom flatwire cable and the standard electronic box is a connector box placed adjacent to the electronics. Inside is a small circuit board that does the mechanical transformation between the planar geometry of the flat cable and the typically round connector. An insulation displacement connection makes contact to the flatwire while a standard coaxial or RJ45 connector attaches to the circuit board.
For example, Figure 1 shows the two metal layer pattern for an Ethernet-equivalent cable and the interface box with an RJ45 jack.
Figure 1. Ethernet-Equivalent Cable and Interface Box
This cable is two metal layers with a “fishlips” pattern. Weaving back and forth between the layers mimics the minimal far field radiation pattern of twisted pair. The precise line width and spacing and dielectric thickness is designed to achieve the target 100 Ohms differential impedance. For this specific design, Southwire measured the attenuation as less than 0.6 dB/foot at 1 GHz, compared with 0.5 dB/foot measured for CAT6 cables.
Martin believes the ultimate performance of flatwire cables can be as good as or better than traditional round wire in CAT5 and CAT6 cables because of its flexibility in pattern design. The combination of enhanced electrical performance, low manufacturing cost, low impact installation, and invisible footprint offers a unique combination of features for residential applications.
This and other signal integrity topics are covered in Eric’s public classes and online lectures, available from his website, www.BeTheSignal.com. Send your signal integrity technical questions to DoctorIsIn@BeTheSignal.com.
Bio: Eric is president of Bogatin Enterprises, whose mission is to set the standard for signal integrity training. He is the author of Signal Integrity - Simplified, published by Prentice Hall. Check out his public signal integrity classes posted on www.BeTheSignal.com. He can be reached at eric@BeTheSignal.com.
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