HDTV Cabling Options Continue to Evolve
The moving image is with us more often than ever, thanks in part to continuous connector innovations.
By Bob Hult, Bishop & Associates Inc.

Connectors that bring content signals to a television have experienced a continuous stream of upgrades as display technology evolved from black and white small-screen CRTs to wide-screen DLP, plasma, and LCD technologies. As screens became larger and high-definition digital signaling become standard, the home theater and the quest for higher fidelity sound and images took off.





Not so long ago, the only connector on the back of a television was a simple two-screw terminal strip that was used to terminate 300 ohm transmission line coming from the antenna.

As users shifted from antenna to cable for the source of programming, the industry adopted the very low cost 75 ohm F type coaxial connector, which offered increased bandwidth and image sharpness.




The TV continued to expand as a display for an increasing number of external devices, including VHS cassette videotapes, DVDs, Blu-ray players, video games, and connections to computers. One approach to higher quality was to split off the analog video signal into three separate cables. Component Video cables using RCA plugs offered better picture resolution.



Composite Video cables carry all the information needed to deliver video-only signals using a single RCA plug.




S-Video cable assemblies are another analog interface that use a four- pin mini-Din connector to deliver video information.

As connections to the TV improved picture quality, demand for higher performance video connectors between a computer and a display device also began to grow.





The 15-pin high-density D-sub video graphics display (VGA) connector was established as the defacto standard for nearly all CRT to desktop computer applications.

The introduction of the 24-plus 4-pin Digital Video Interface (DVI) in 1999 by the Digital Display Working Group was a departure from prior video connectors in that it was designed for transmission of digital signaling, and was developed specifically for personal computer to display applications.



In 2006, the Video Electronics Standards Association (VESA) introduced DisplayPort, the first of a new generation of video interface standards that transmits packetized digital information. Display Port replaced DVI and VGA in high resolution display applications. It combines the ability to transmit both audio and video information in the same cable assembly at up to 5.4 Gb/s per lane. The most current 1.2 specification increased the bandwidth to over 17 Gb/s/ DisplayPort 20 position connectors and cables offer increased image resolution, faster refresh rates, improved color and support for emerging 3D content. The connector and cable are much thinner and lighter than its predecessors, greatly simplifying cable management issues.

The reduced size of a DisplayPort connector is a major advantage at the back of a crowded laptop computer.

The version 1.2 specification approved in 2009 also includes a Mini DisplayPort connector originally developed by Apple Computer that offers even greater density in an 8.3mm wide by 5.4mm high interface.

The DisplayPort standard defines passive cables that deliver full bandwidth at up to 3 meters in length. The use of active cables that feature integrated signal conditioning devices can extend this length to 33 meters.

DisplayPort has been widely implemented in desktop and laptop computers between the video graphics card and the monitor, but is also seen as a contender in the consumer HDTV market.

The majority of HDTVs today include multiple ports of the High Definition Multimedia Interface (HDMI), which have become the most common interface on consumer video equipment.

Introduced by HDMI Founders, an industry consortium in 2003, the 19-pin type A connector has a bandwidth of 10.2 Gb/s and can deliver 3D video, and Ethernet channels, in addition to HD video and audio.

Over the years HDMI specifications have evolved to include five connector types.

Type A is commonly seen on consumer audio and video equipment.

Type B connectors have 29 pins and double the bandwidth of Type A. Type B connectors will likely be implemented in future generations of video displays.

Type C mini connectors as defined in the HDMI 1.3 specification retain the 19 contacts in a reduced profile interface, and target portable devices.

The most current 1.4 specification defines a Type D 19 pin Micro connector that is similar in size to the micro-USB. Typical applications include hand-held smart phones, video cameras, and navigation devices. This specification also includes a Type E connector that features positive latches and is specifically designed for automotive applications.

Unlike the DisplayPort specification, HDMI standards do not define a maximum cable length. The signal integrity of the link is determined by quality of the cable materials and construction. A series of qualification test parameters are defined in HDMI 1.3 and include interpair skew, far end crosstalk, attenuation, and differential impedance. Standard cables support version 1.0 and 1.2, while High-Speed cables are certified to versions 1.3 and 1.4. Commercially available HDMI cables today range in length from 3 to 15 meters.

The newest kid on the block is Thunderbolt, a 10 Gb/s bidirectional interface jointly developed by Intel and Apple Computer.  The Apple iMac and MacBook Pro series were the first products to sport this new high-speed interface, while other computer makers have yet to add a Thunderbolt port. Initial criticism centered on the lack of peripherals that can take advantage of 10 Gb/s transfer rates, but new RAID storage devices that utilize a Thunderbolt port have been introduced.

Most initial reviews compared Thunderbolt to USB 3.0, which operates at up to 5 Gb/s. A unique aspect of Thunderbolt technology is its ability to support PCI Express as well as DisplayPort over a single cable. Since the connector is a slightly modified Mini DisplayPort interface, a standard Mini DisplayPort connector can plug directly into a Thunderbolt receptacle. Multiple high-speed peripherals such as external storage, video capture, and video display devices can be daisy-chained with no loss of throughput while reducing cable clutter.

In order to move data at these high speeds over copper, the specification defines the use of active cables that add cost. These assemblies are currently available from a very limited number of sources.

At this point, it is unclear how widely Thunderbolt technology will be accepted, or what its impact will be on connections to the TV. Home theater applications would not see much advantage to 10 Gb/s speed, and the current limitations on Thunderbolt cable length would pose a serious restriction. On the other hand, one should never discount the influence of two major technology leaders on any market they would chose to enter.

Bishop & Associates Inc. Comments: 

• DisplayPort, HDMI, and Thunderbolt each offer high-speed, consumer-friendly interfaces that are being positioned to address emerging computing and HDTV applications. All offer significant improvements in packaging density, a critical factor in I/O panel real estate decisions. 

• HDMI is the current leader in HDTV and high-performance audio applications, while DisplayPort dominates computer to display applications.  

• Thunderbolt initially targeted computer to storage peripherals, but has the capacity to support high definition video displays. The Thunderbolt roadmap may include a future optic option that could bump the bandwidth to 100 Gb/s. 

• FireWire (IEEE 1394) continues to evolve with proposed higher speed and mini connector upgrades. New applications for FireWire include industrial vision systems and camera-related products. 

• The latest version of DisplayPort offers higher bandwidth and longer cable lengths than HDMI, but these advantages bring little value to the average HDTV consumer. 

• All signs indicate that DisplayPort and HDMI will continue to coexist and serve their original target markets. Thunderbolt may be a wild card depending on development of applications that can take advantage of its expanded bandwidth headroom and flexibility. The long anticipated convergence of home entertainment and personal computer (media center) may ultimately change the balance between these interfaces.

Robert Hult Director of Product Technology, Bishop & Associates Inc. Robert Hult has been in the connector industry for more than 36 years. Hult began his career as a sales engineer for Amphenol. He joined AMP in 1972 and served in several management positions through 1996. In 1997, Hult joined Foxconn as group marketing manager for Intel in Chandler, Arizona, U.S. Prior to joining Bishop & Associates, Hult was the regional application engineering manager for Tyco Electronics. Hult graduated in 1968 from Bradley University with a bachelor of science degree in electronics technology and a minor in business.