The television has undergone a remarkable transformation over the past decade. Driven by the ongoing digital revolution and well-defined HDTV (high-definition television) standards, TV performance has taken a giant leap forward. Until recently, TVs built to popular analog standards used the 480i format to deliver the 720H x 480V interlaced images that resulted in a conventional TV viewing experience. Today's TVs are rapidly moving to the 1080p standard, which defines a 1920H x 1080V image that delivers stunningly realistic HD video quality.
The audio "soundscape" also is changing rapidly. While existing home theater systems provide high-fidelity Dolby 5.1–channel Surround Sound, future systems will support 7.1-channel audio. And high-definition audio will deliver to users audio that, for the first time, can be bit-for-bit identical to studio masters. Such audio and video processing innovations are taxing the performance of today's multimedia interfaces that connect the components of a home entertainment system, whether in a single cabinet or distributed through the home. This is giving rise to new standards aimed at improving interface and cable quality to ensure HD sound and images are synchronized and that consumers can more easily configure their HD systems.
And further performance enhancements are on the horizon.
The following examines recent trends in ATV video, audio and interconnect design; explores the impact those developments are having on consumers' entertainment experiences; and discusses how engineers at Analog Devices are addressing the challenges of next-generation ATV design.
Signal Processing Defines the ATV Experience
Ironically, the so-called "digital TV" revolution would not be possible without a concurrent revolution in analog signal processing. While today's HDTV systems are defined by their ability to deliver spectacular digital image and sound clarity, the quality of the multimedia experience consumers have come to expect depends directly on how well the analog signals are captured, processed digitally, and reproduced. In other words, delivering home theater-quality entertainment is based largely on a systems designer’s skill at overcoming a number of imposing challenges in the analog and mixed-signal domains.
Analog Technology Defines Digital TV
As an established industry leader in analog and mixed-signal processing technology, Analog Devices has unmatched insight into the challenges facing advanced TV (ATV) designers. Through its Advantiv™ advanced television solutions portfolio, ADI offers the industry's broadest array of high-performance ICs to meet the analog and digital video processing, audio processing and connectivity challenges in digital TV and home entertainment systems.
The evolution of TV video quality and the rapid rise in video bandwidth requirements over the past few years has been nothing short of remarkable. While 480i analog systems required only a 6 MHz bandwidth, today's 1080p-compliant systems deliver a 1920H x 1080V image, which requires data delivered at 148.5 MegaPixels/second (MPPS). This has contributed to much more realistic images; progressive scanning (as opposed to interlaced) doubles the data rate, but results in much smoother motion with far fewer artifacts.
A similar evolution has occurred in color depth. Most currently available HDTVs offer 8-bit color (meaning 219 levels of brightness for each of the three colors making up a picture element, or pixel). Emerging new "deep color" standards for video increase this resolution to 3504 levels per color (using 12-bit color). Moving to a new color space, called xvYCC, raises this to a full 4096 levels per color and delivers the most realistic images consumers have ever seen. Of course, this also increases the amount of data that needs to be moved around the home by a factor of more than 18. The problem ATV designers must address is how to deliver these vivid high quality images at a price point the average consumer can afford.
To manage this explosion in data rates, the ATV industry has turned to video compression technology. While there is a growing variety of video compression COder DECoders (CODECs) available, they are generally based on the Discrete Cosine Transform (DCT) with inter-frame motion estimation to achieve very high levels of compression. These CODECs (such as MPEG-2, MPEG-4, H.264, AVC, and others) are very efficient, but they are extremely computation-intensive on the compression side. Efficiency comes at a cost. This cost is entirely appropriate for the distribution of television programming and films over the air, satellite, cable, or DVDs, where the available bandwidth is severely constrained and the application is "compress once, decompress many."
In the home entertainment system of the future, however, a different environment exists. With modern RF, coaxial, network, and powerline transports, far more bandwidth is available; signals exceeding 100 Mbps are commonly distributed. At the same time, there are numerous applications were it is necessary to compress an HD source in the home, in real time, at low cost. DCT-based inter-frame compression is ill-suited to this task.
Analog Devices has been a pioneer in an entirely new class of compression algorithms based on wavelet mathematics. ADI started work in 1993; this approach was standardized by the JPEG committee at the end of the decade and named JPEG2000. Now internationally recognized, JPEG2000 technology applies two-dimensional filtering and sub-sampling in hierarchical and multi-step combinations. This offers a number of advantages, including scalability of the image when decompressed without further processing, robustness and immunity to transmission errors, very low compression and decompression latency, and low-cost compression hardware.
Analog Devices introduced its first wavelet-based video compression IC in 1996. Since then the company has been a leading developer of JPEG2000 compression components through its Wavescale™ compression technology and now supplies the digital compression technology used by Hollywood studios for the Digital Cinema Initiative (DCI), a move to distribute feature films worldwide electronically and eliminate the production and shipping of reels of film. Recently, Analog Devices began applying that same digital compression technology to HDMI™ (High-Definition Multimedia Interface™) systems, enabling wireless transmission of HD quality video within the home. In the near future, ADI's Wavescale compression technology will allow users to enjoy the same HD image quality anywhere in their homes without the cost or complexity of running cables to every room.
A second challenge ATV designers face in the video realm is establishing compatibility across a wide variety of legacy signal types still supported in today's HD systems. Many consumers, for example, want to replay old movies, VHS tapes or use older DVD players with their new HDTVs. But many legacy standard-definition video sources are of marginal quality; what looked okay on a 27" standard definition display may look terrible on a 50" HDTV. High-performance analog signal processing based on high-resolution data conversion and advances in video filtering play a key role in bridging the gap between these technologies and letting users enjoy content from a variety of sources on an HDTV system while minimizing disturbing artifacts.
To address this problem, Analog Devices has developed an unmatched catalog of video components as part of its Advantiv solutions portfolio. The company offers an extensive line of video encoder and decoder ICs that automatically digitize and convert SDTV, EDTV, HDTV and PC-RGB signals for use in digital displays and meet all the standards for video transmission, re-distribution, editing and storage in professional and industrial applications. ADI's video CODECs offer designers both the performance and the flexibility to support the many analog formats that conform to international SDTV and HDTV standards.
Designers building audio systems to match the quality and clarity of the HD picture face a multi-faceted challenge. Audio sources to the TV, via digital broadcast or HDMI connection to DVD players or latest generation HD players, now have the capability of providing multi-channel programming with high resolution and sample rates. Meanwhile the TV has remained, for the large part, a stereo audio device that requires some flexible audio post-processing to enable a "Surround-Sound" experience through two speakers. This process of surround-sound virtualization, as well as the process of spatialization (spreading) of conventional stereo content, are increasingly used in HDTV systems to enhance the user listening experience.
At the same time the shrinking outline of flat-panel HDTVs has created additional difficulties for TV designers. The thin cabinet form factor forces the use of small, thin loudspeakers that may not be as efficient at reproducing the lower (bass) frequencies increasingly being used in modern movie sound-effects and popular music. To overcome this deficiency, additional audio processing is required to dynamically enhance the bass frequencies. In modern flat-panel TVs, conventional linear amplifiers cannot be used because they require large heatsinks. Flat-panel TVs require higher efficiency amplifiers that need little or no heatsinking. This requirement for increased efficiency also supports the "green" trend in TVs towards lowering power consumption during operation and standby.
Analog Devices' TV audio processors can be optimized via software for different combinations of speakers and cabinets. These processors offer a comprehensive portfolio of audio enhancement algorithms, including those from well-known third party suppliers, to adapt TV audio playback to the multi-channel, high resolution audio sources now available. For the tight space constraints of flat panel HDTVs, Analog Devices' audio line includes Class D amplifiers that operate with small or no heat sinks.
To leapfrog the performance limitations of conventional analog A/V connectors, a number of leading electronics manufacturers joined together in 2002 to throw their support behind a new digital interconnect called HDMI™. By eliminating compression and analog-to-digital conversion, HDMI allowed audio and video signals to remain in digital form from the output device to the display and, in the process, preserve the original quality of the source content. Moreover, the new connection standard dramatically reduced wiring complexity by replacing up to eight audio and five video cables with a single cable for HD video, multi-channel audio and intelligent format and command data.
The latest version of the interface standard, HDMI 1.3, takes this performance to the next step. It allows designers to build systems with higher levels of video accuracy by representing more shades of gray, supporting higher contrast ratios and smoothing tonal transitions by eliminating the on-screen banding between gradations of color. With the HDMI 1.3 standard, single-link bandwidth rises to 10.2 Gbps. It also optionally supports deep-color - 30-bit, 36-bit and 48-bit – as well as the new xvYCC color space. Audio performance dramatically improves as well with support of lossless compression formats such as Dolby TrueHD and DTS-HD, provided on many HD DVD and Blu-ray discs.
Still, designers using this increasingly powerful interface must address a number of obstacles. Product compatibility remains an issue, although compliance testing has begun to address the need for guaranteed interoperability. Support for longer cables also presents a problem as HDMI cable runs typically are limited to 10 or 20 meters. HDMI's support for High-bandwidth Digital Content Protection (HDCP) and Consumer Electronics Control (CEC) will play a major role in future home theater equipment designs. To ensure content protection, Hollywood studios are requiring all new high-definition DVDs be encrypted for use only with HDCP-enabled DVD players and HDTVs. CEC allows consumers to operate their HDTVs, DVD players, HD camcorders, and other compliant equipment through a single remote control, eliminating the clutter and confusion that comes from juggling multiple remotes and menus.
With abroad line of HDMI ICs, Analog Devices is helping designers address these issues. ADI's HMDI 1.3-compatible multiplexers, receivers and transceivers support the delivery of new levels of picture quality in applications ranging from 1080p HDTVs to digital video and still cameras, portable media players and cell phones. Included in the Advantiv product line are the industry's first buffered multiplexers to support 1080p deep color technology as defined in the HDMI 1.3 standard. The new multiplexers also add proprietary equalization technology that allows them to transmit signals over more than 20 meters of HDMI 1.3-compliant cable. More recently, Analog Devices has given users even more flexibility to position home theater equipment by using its own video compression technology to develop the first HDMI solutions for wireless connectivity. Analog Devices has also introduced the industry's first HDMI transmitter to offer on-chip CEC support to help simplify the use of HDTV and home theater equipment.
The ATV era has just begun. Analyst firm DisplaySearch predicts that the HDTV market will grow by 65 percent over the next five years as prices for high performance ATVs decline. To drive that growth, ATV equipment designers must design high performance TVs and companion devices including digital video recorders (DVRs), audio/video recorders (AVRs), HD video camcorders and set-top boxes capable of delivering the vivid images and vibrant sounds consumers expect in next-generation home entertainment systems. With its unique position as a leading developer of analog signal processing technologies, its extensive experience with ATV equipment developers, and its broad portfolio of ATV products, solutions and design support, Analog Devices is providing the building blocks and systems expertise designers need to optimize their next-generation equipment for the ATV market.