One of the biggest engineering challenges remaining for
tomorrow's advanced digital set-top boxes is making sure the old analog past
isn't completely left behind.
But developing a single set-top tuner chip that handles
digital and analog video signals, as well as upstream and downstream data signals, has
proven elusive.
The semiconductor industry has responded to the lucrative
market potential of silicon tuners with several announcements over the past year.
The latest comes from Microtune Inc., a Plano, Texas-based
developer of RF silicon products, which today (March 13) debuts its third-generation
tuner-chip family, including the "MicroTuner 2030-STB" for set-tops.
Microtune said the new chip supports both digital and
analog signal conversions. It also complies with the Data Over Cable Service Interface
Specification, 256 quadrature-amplitude-modulation, vestigial-sideband modulation (8-VSB),
National Television Systems Committee, Digital Audio/Video Interoperability Council,
Digital Video Broadcast and phase-alternation-by-line (PAL) standards.
Microtune also released the "MM8838 MicroModule,"
which contains the MicroTuner 2030 chip, a diplexer to separate digital/analog video from
data signals, an out-of-band tuner, and other RF components. The module is targeted toward
set-top original-equipment manufacturers seeking to purchase complete RF circuitry for
set-tops.
High-performance, multifunctional tuners are a key link in
the overall OpenCable network platform, the specifications of which are being developed by
Cable Television Laboratories Inc.
"A good tuner design is absolutely critical to system
performance," OpenCable director of advanced platforms David Birks said. The tuner
"really sets the performance bar for the whole system," Microtune chairman
Douglas Bartek added.
To reinforce his point, Birks said, an RF signal first
enters a receiver or set-top via the tuner, and no matter how pristine the signal is
entering the device, tuner design affects the ultimate performance of the video picture.
While OpenCable is not attempting to define specifications
for tuner chips or tuner-chip design, interim specs have described noise levels and
RF-transmission characteristics that typically occur in a system for 64 QAM, 256 QAM and
AM-VSB signals. These levels must be compensated for when crafting tuner chips.
Birks added that there's still a lot of variability in
the performance of tuner designs. "Some are very good at analog, but not as good for
digital [signals]," he said. The challenge is to design a chip that successfully
converts both analog and digital.
To complicate matters, signal noise affects each analog and
digital signal differently. Noise "gracefully degrades" analog signals, creating
"snowy" pictures, while a digital signal, initially unaffected by noise,
eventually reaches a "cliff" where the video picture simply goes blank, Birks
said.
Bud Taddiken, vice president of integrated-circuit
engineering for Microtune, said that by addressing four critical metrics of digital-signal
performance -- noise, phase noise, gain flatness and integrated-frequency flatness -- plus
composite triple-beat and composite second-order effects for energy-laden analog signals,
the company has addressed the major digital and analog tuning issues in its new chip.
Microtune's chip uses a bipolar complementary
metal-oxide semiconductor technology. According to Taddiken, power-consumption levels for
the new 2030 chip have been lowered compared with those of its predecessor, the
"MicroTuner 2000." Also, the size of the new chip has been reduced by one-third
compared with its predecessor.
Today's digital set-tops contain two discrete tuners
-- one for analog signals and one for digital. By engineering all of the tuner componentry
on a single chip, a set-top manufacturer realizes significant savings in the valuable real
estate of advanced digital set-tops.
Yet the tightly knit, highly integrated components are
susceptible to noise, which challenges the design expertise of chip makers.
"We're clearly seeing a lot of progress in that
arena," said Bill Wall, technical director for subscriber networks at
Scientific-Atlanta Inc. But he added, "The big issue for us right now is analog
[tuning]."
While Wall said, "We're very interested in what
we're seeing" from single-chip tuners, and "a number of solutions are very
close to being viable," he conceded that no single-chip solutions S-A has tested are
quite up to the task yet.
"I have not seen any chips that are really meeting all
of the specs for analog performance," he said, adding that the single-chip tuner is
"one of the toughest portions of set-top engineering."
S-A's next-generation "Explorer 6000"
contains traditional discrete tuners that can handle analog/digital tuning, as well as
out-of-band tuning for data-channel reception, Wall said.
While it remains to be seen whether or not Microtune has
unlocked the keys to the single-chip tuner, the company's new releases are targeting
the broad potential market for such a device.
The number of silicon tuners sold for digital and color
TVs, satellite set-tops, cable set-tops and VCRs will hit 31 million this year, growing to
112 million units in 2003. Responding to this market potential, Microtune has developed
versions of the new 2030 chip for set-tops, cable modems, PC/TV applications and digital
TV sets.
Microtune's MM8838 MicroModule is the first fruit to
sprout from its January acquisition of German RF firm Temic Telefunken.
While Bartek declined to acknowledge a report that the
acquisition and subsequent module release were driven by a contract obligation Microtune
made with a major set-top vendor, he agreed that a modular device could entice set-top
makers that are new to the cable industry to produce boxes based on the OpenCable
architecture.
While Microtune may claim a technological edge in
single-chip, dual-conversion tuners, competition is not far behind.
In December, Broadcom Corp. introduced a TV-tuner chip
capable of digital tuning in cable modems and set-tops based on its "BCM3400"
chip technology. Also in December, Conexant Systems Inc. released a digital-chip tuner and
Silicon Wave Inc. released a dual-conversion tuner.
Broadcom said it will release a chip that will handle both
analog and digital tuning in late April or early May. Sarnoff Corp. is also planning a
prototype tuner chip this year
