hdmi-cables

Technological obsolescence is a real threat for both the developers of the technology as well as its consumers. And, companies continue to invest in innovation in order to exploit the ephemeral nature of technology leading to a conundrum. However, what takes time to establish and lasts longer is the application of the new technology. Thus we have HDMI-enabled devices that have been around for a while but only started gathering momentum lately. And the resurgence is so robust that by the end of 2012, over 750 million pieces of HDMI-enabled devices would have hit the retail shelves dominating the consumer electronics space.

High-Definition Multimedia Interface (HDMI) has been around for over five years now. The recent developments in the convergence of consumer electronic goods have catapulted HDMI to the forefront of technological advancements. Its ease-of-use and the promise of an uncluttered interface while being able to carry uncompressed digital audio/video streams over the same interconnect give consumers and OEMs enough reasons to pile on HDMI. Today, HDMI is the interface of choice for Blu-ray players, flat-panel HD televisions, video-game consoles, PCs, HDTV camcorders, and digital still cameras.

On a single HDMI cable, multiple TV or PC video formats – standard, enhanced, and high-definition video – NTSC, and PAL are supported along with up to 8 channels of 24-bit uncompressed digital audio at 192 kHz. If that sounds like a stretch, then this spec has enough bandwidth left for accommodating future enhancements. Let us find out how the cable supports the digital audio/video transfer without causing degradation of the signal through compression/decompression processes.

The HDMI cables are made of pairs of twisted copper wire of specified lengths extending up to a maximum of 15 meters (around 50 feet). By design, HDMI uses long copper cables without requiring amplifiers or repeaters. Though the HDMI standard does not specify a maximum cable length, it is known that over long distances copper cables carrying high density digital data are prone to signal degradation in the absence of an error correction mechanism. As a result, the HDMI spec only provides prescriptive information about cable length, quality, and affordability for maximum data throughput.

Transporting audio and video signals along the same channel is achieved by incorporating TMDS encoding protocol in the HDMI design. Transition minimized differential signaling (TMDS) protocol is a unique, precision-controlled algorithm with built-in error correction feature. With TMDS, data transfer happens between a ‘source’ and a ‘sink’ or monitor when the device switches between on and off states. Thus the source of data such as an HDMI-enabled digital satellite TV set-top box is able to transmit data to the sink such as a digital television without signal attenuation. Excessive transitioning is kept in check to avoid high electromagnetic interference (EMI) levels on the interconnecting HDMI cable with the help of advanced encoding algorithm. The technology also succinctly handles detection errors resulting from long strings of ‘0’ and ‘1’. The entire process of encoding converts 8-bit input data into 10-bit transition-minimized DC-balanced making HDMI cables a veritable asset in the digital audio/video world.

The HDMI cable may use a single link (Type A or C) or dual link (Type B) connection. An HDMI link has three TMDS data channels each with a separate differential pair on the HDMI cable. With this, HDMI cables attain to audio and video data transfer equivalent to 165 million pixels per second (pixel clock rate of 165MHz). The TMDS Clock, a fourth differential pair, provides the pixel clock for timing the data stream. A single link connection can have a video pixel rate of 25-340 MHz and a dual link supports 680 MHz.