Modem Chips Mesh Analog and Digital into One
by Gene Koprowski
8:56am 11.Dec.97.PST
A breakthrough in the design of modem chips will
integrate both digital and analog functions on the
same system, an innovation that is expected to
reduce manufacturing costs for developers and
power requirements for users. In an effort between
3Com and semiconductor manufacturer Analog
Devices Inc., the new design - for a 56 Kbps
modem - will integrate five digital and analog chips
onto a single silicon chip.
The technology is the first to integrate
mixed-signal and digital-signal processing on a
single chip. The chip, which is expected to
premier by the middle of next year, has secretly
been in the works since 1995, with the US
Robotics unit of 3Com, says Maury Wood, a
product line director for Analog, based in Norwood,
Massachusetts. The technology replaces chips
produced by Texas Instruments Corp.
"If you look at the current Sportster modem, they
have five [integrated circuits], including data
converters, a [digital signal processor], and two
separate memory chips and an
[application-specific integrated circuit], which
allows you to interface to the PCMCIA bus," says
Wood. "This device integrates all of these
functions into a single piece of silicon. That saves
money and will enable them to put the chip on a
single circuit board."
Rockwell, 3Com, and Motorola recently came to
terms on a standard for 56 Kbps modems, and a
preliminary version of that specification is due in
January. 3Com's x2 modem technology, acquired
when the company bought US Robotics earlier
this year, was one of the two de facto standards
which some 1,200 ISPs already support. A key
benefit of the new chip design, 3Com claims, is
thatit will consume 50 percent less power than
current chips, and have "power management
features that go well beyond what is in the current
chip set," says Wood.
These chips will not be made at the company's
plants in the United States, but are being
fabricated at a plant near Taipei owned by the
Taiwan Semiconductor Manufacturing Corp. "They
can produce it much more cheaply than we can,"
says Wood.
An industry analyst at Dataquest said the
single-chip solution is a "significant breakthrough"
in the functional integration of analog and
mixed-signal digital signal processors. "The issue
is that the DSPs are digital circuits, made using
the standard, sub-micron, [complimentary metal
oxide silicon] process technology, and have a
small size. But analog chips have a very large
feature size," says Jim Liang. "DSPs need small
feature sizes for high-speed switching, but the
analog chips, or mixed signals, need larger sizes
for performance. However, in these products, such
as modems, you need both digital and analog
functions in the same system."
Integrating the two technologies was quite an
accomplishment, for, not only have they
historically differed in size, they have also had
completely different manufacturing processes. To
solve this, 3Com built one mask to do it at the
same time.
One potential problem that technologists fear: the
digital processors could conceivably interfere with
the signals emitted by the analog chips. But
Dataquest's Liang thinks they will avoid this
problem. And this reduced signal interference will
make it easier for 3Com to obtain FCC approval,
says Jerry Devlin of 3Com.
Concludes another analyst, Will Strauss,
president of Forward Concepts, a market research
consultancy based in Tempe, Arizona: "The ability
to integrate an analog front-end with a DSP is the
future of many emerging high-volume consumer
applications. This single-chip solution for 3Com's
US Robotics 56K modem clearly places [Analog
Devices] at the cutting edge of this technology." |
