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Inside HDBaseT Technology: A Better HDMI Extender

HDBaseT delivers 4K x 2K video, audio, control, Ethernet and up to 100 watts of power over a single Cat 5 cable up to 100 meters ... without degrading the signal. How'd they do that?


HDBaseT: One Cat 5 cable for 100 meters of uncompressed video, audio, control, Ethernet, power, HDMI pass-through
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If it is implemented on a large scale, HDBaseT could be an exciting development in whole-house multimedia distribution—enabling video resolutions (4k x 2K), distances (100+ meters) and extra features (100 watts of power) that we’ve never seen over a single Cat 5 cable.

The technology originally was developed by Valens Semiconductor and marketed under the 5Play brand. Now the official HDBaseT 1.0 spec has been ratified  by the six-month-old HDBaseT Alliance formed by Valens, LG Electronics, Samsung Electronics and Sony Pictures Entertainment.

Contrary to overzealous reports, HDBaseT is not a replacement for HDMI—and will not be a replacement anytime soon.

In fact, the technology is simply an enhancement to HDMI. It still requires an HDMI chipset at both the transmitting (source) and receiving (display) ends – just like any other HDMI-over-Cat 5 solution.

In any case, “We’re not trying to be an HDMI extender,” says Micha Risling, VP of sales and marketing for Valens Semiconductor and spokesperson for the HDBaseT Alliance. “It’s only one segment that we’re after simply because we can. But we’re trying to introduce much, much more than that.”

In the HDBaseT universe, video, audio and related data signals are processed by the HDMI chip as usual, and HDBaseT takes it from there.

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FIGURE A: The Valens VS100 System Functional Diagram

Building a Better HDMI Extender

Most of today’s better HDMI extenders utilize two runs of Cat 5 or Cat 6 twisted-pair cables.

Typically, one cable is reserved for TMDS, transmitting video, audio and associated timing clock signals. The other carries the handshaking signals (with customized electronics for maintaining signal integrity) and low-current power for driving the HDMI electronics at the receiver.

HDBaseT: The Whole Picture
I. HDBaseT Cat 5 Technology is Useful, but No ‘HDMI Killer’
II. Inside HDBaseT Technology: A Better HDMI Extender
III. Is HDBaseT a Game Changer? (coming soon)

More vendors now are going the one-wire route, using proprietary schemes to push the audio, video, control and power over the cable without compromising performance … much.

In both cases, the cables are susceptible to the same electromagnetic interference that plagues any transmission of high-frequency signals over long wire runs.

To mitigate EMI, HDBaseT transmits lower-frequency modulated signals across the cable using Pulse Amplitude Modulation (PAM) – the same technology used for coding Ethernet signals onto twisted pair cabling.

With this method, digital data is represented as a coding scheme using different levels of DC voltage at fairly high rates (in the order of 125 mega pulses per second or more for Ethernet).  While 100BaseT Ethernet uses 5 Level PAM (PAM-5), HDBaseT uses a proprietary version that is slightly different.  Some of the newer high-speed Ethernet coding schemes, like 802.an (10GBaseT), use 16 Level PAM.

In the case of HDBaseT, PAM is used to “modulate” all of the HDMI and control signals onto each set of twisted pair wires. The magic is in the proprietary coding scheme used to get all of that data onto the wire bundle, allowing content to be sent across a single Cat cable without being degraded by the electrical characteristics of the wire.

It is important thing to note that, while HDBaseT uses the same coding technology as Ethernet and does have an Ethernet channel, it is not Ethernet based. It does not use Internet Protocols (IP) either. It just happens to use the same type of twisted pair cable that most associate with Ethernet.

Translating HDMI to HDBaseT

To really understand what HDBaseT is all about, it is useful to take a look at the chipsets themselves.

Valens currently is the only provider of HDBaseT chips – the VS100TX transmitter and the VS100RX receiver.

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FIGURE B: Valens VS100TX Transmitter High-Level Block Diagram

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FIGURE C: Valens VS100RX Receiver High-Level Block Diagram

The pins of interest initially are the TMDS lines that interconnect directly with the TMDS lines on the associated HDMI transmitter or receiver chip.

Although we’ll refer to the designators from the transmitter (VS100TX in Fig. B) for this example, the concepts are the same for the receiver as well.



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