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TV On Your Own Terms: Using Advanced SiGe-Based IC Technology to Enable True Video-on-Demand Applications
By Kirk Ashby, IC Design Manager, Microtune, Inc.

Video-on-demand (VOD) is an attractive service that has yet to truly live up to its promise. VOD technology is capable of delivering selections from an entire video library (such as movies, television programs, educational programs, and archival video) directly to the consumer's television with full VCR-like functionality including fast-forward, rewind, and pause features.

With such impressive capabilities, what is holding it back? At the root of the problem are the size, cost, and power consumption of the VOD system hardware, used to deliver the hundreds of dedicated channels required for VOD services.

Business Issues: Cost, Size, Power

Figure 1 shows a simplified example of an upconverter application in a cable television system. An upconverter is used to translate programming information from a fixed intermediate frequency (IF) (typically 44MHz in the US or 36MHz in Europe) to a final output frequency (between 50MHz and 860MHz) for distribution on the cable system. For traditional network programming, the upconverter cost is distributed over the many thousands of potential viewers of that program, resulting in a low distribution cost.

For a VOD system, a program may have only one viewer resulting in a very high distribution cost. To reduce this cost, digital compression techniques are applied to allow the simultaneous transmission of up to 10 different digitized programs (or streams) in the same bandwidth as a single analog channel. Even with these savings, the cost of the equipment needed to distribute a single stream of digital programming ranges from $100 to $200. A traditional rack-mounted upconverter contributes a significant portion of this cost.

Click for larger image
Figure 1:

While the costs of other required components in a VOD system have come down over the years, the cost of implementing the upconverters is still high and has made the implementation of a full-featured VOD service cost-prohibitive.

Physical size is another important parameter in cable headend equipment. Many cable operators already have overcrowded facilities, and rack space is at a premium. In recent years, significant progress has been made in reducing the size of discrete based upconverters. However, if VOD is successful, a much larger number of upconverters will be needed and their size will need to be much smaller than today's smallest upconverter.

As cable operators consider moving some headend functions further out into the neighborhoods they serve, size again becomes a concern since the equipment needs to fit inside a small enclosure that can be mounted on a utility pole. As a result, integrating the upconversion in silicon and greatly reducing the overall footprint could save a great deal of space in the headend and enable distributed services.

Overcrowded cable headend facilities are also a concern for power consumption-not only for the equipment, but also for the cooling costs required to keep it functioning. Traditional upconverter solutions feature typical power consumption of 10 to 20W/channel.

Technical Challenges

In addition to cost, size, and power, size, issues, the upconverter must meet difficult technical specifications. Because the system is broadband, any spurious signals or noise generated by the upconverter will likely fall inside a band occupied by another channel. To prevent degradation of other channels, spurious signals and noise must be kept to very low levels. In discrete based upconverters, this has been achieved by dividing the output spectrum into bands and applying filters to each band. This results in an expensive, bulky, and power hungry design.

A New Approach

Microtune has combined silicon germanium (SiGe) process technology from IBM Microelectronics with a patent-pending new architecture and advanced circuit design to create a three-chip upconverter solution called the VideoCasterý. The chipset includes the MT5011 upconverter, the MT5012 downconverter, and the MT1150 driver amplifier. For those customers who prefer a modularized solution, Microtune has also leveraged its expertise to create a compact four-channel MicroModule based on the new chipset. This fully tested module includes all of the required heat sinking, physical interfaces, and shielding/isolation between channels.

A single 3.5 by 4-in MicroModule can support up to 40 streams of digital video. This replaces four 19-in rack-mounted upconverters and can reduce upconverter volume by 90% (Figure 2a, 2b). A single channel of upconversion implemented with the VideoCaster chips set consumes only 6W, resulting in power savings of 40% or greater compared to a traditional discrete based upconverter.

Figure 2a
The VideoCaster chipset provides the functionality of a typical VCR-sized upconverter.

Figure 2b
By using an enabling manufacturing process and careful circuit design,
a silicon-based VOD design can replace four rack-mounted upconverters
with a significant reduction in size.

The use of SiGe contributes significantly to the performance and reduced size of the new upconverter solution. Some of the advantages offered by this process (as compared to standard silicon devices) include higher operating frequencies, lower noise figures, lower power consumption, and improved linearity. Of course, it is still a silicon process, so SiGe can benefit from the low cost, high yields, and high integration associated with silicon devices.

The VideoCaster chipset architecture includes integrated single-sideband mixers to help with spurious signals as well as feedback circuits to improve linearity (which keeps harmonics low). While effective, these techniques are difficult to implement at high frequencies. However, by taking advantage of the very fast transistor speed of IBM's SiGe technology, designers could still apply feedback at relatively high frequencies to improve linearity and reduce interfering signals.

Microtune's patent-pending architecture takes advantage of the benefits of integration to eliminate the filter banks used by discrete based upconverters. The result is a significant reduction in complexity, size, and power consumption.

Market Possibilities

By applying these and other circuit design techniques, Microtune leveraged the high integration capability of SiGe to develop a small upconverter with low power and cost per video stream. It provides the cable industry with a silicon-based RF technology that enables full-scale and widespread deployment of on-demand movies and other digital content.

The potential revenue-boosting effects for the cable services market are impressive. For the cable operator, full-featured VOD is an untapped market with the potential for substantially increased revenues. In many cases, cable operators have already upgraded their hybrid fiber-coaxial (HFC) digital and broadband networks to include two-way transmissions and to improve the amount of data delivered to their customers. These are the baseline components required to implement a true VOD system. By combining these with a highly integrated, cost-effective upconverter, operators can deliver full-featured VOD services to their subscribers-gaining a significant competitive advantage and a substantial increase to the bottom line.

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