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Maxim > Design Support > Technical Documents > Application Notes > Digital Potentiometers > APP 1769
Maxim > Design Support > Technical Documents > Application Notes > Optoelectronics > APP 1769
Keywords: SONET, SDH, ATM, FDDI, faster ethernet, gigabit ethernet, laser driver, digital pot, laser
drivers, digital potentiometers, digi pots
APPLICATION NOTE 1769
Behind the Light Show in Optical Transceivers
Oct 21, 2002
Abstract: This article explains, in laymen's terms, the growing importance of optic-based
telecommunications and describes the various standards (SDH, SONET, and FDDI) that are being used
to implement this technology. As a young technology, improvements can be made to both improve the
performance of the technology and reduce costs in manufacturing process. Digital potentiometers provide
a means to set critical laser driver and feedback circuits for optimal performance. Temperature sensing
mechanisms inside these pots can be used to monitor and compensate these circuits for any parametric
changes that may occur as a function of temperature. These digital potentiometers can also be used to
automate production calibration procedures once performed manually using mechanical potentiometers
or handpicked fixed resistors. This not only reduces the production cost of these laser drivers, but also
can be used to improve the reliability and quality of the devices by removing the element of human error
from the calibration process. Dallas Semiconductor potentiometers discussed include the DS1845,
DS1846, DS1847, and DS1848.
In recent years, news about communications networks technology always seems to involve some
pronouncement on the urgent need for more bandwidth. The facts still bear repeating: A growing number
of people with telephones, faxes, modems, and computers are, through the exchange of terabytes of
digitized information (videos, images, modeling procedures, as well as data and voice), demanding a
larger share of the carrier spectrum. In response, high-tech communications companies who thrive on
growth are competing to feed this appetite for bandwidth. Over the past decade, major resources have
gone into developing fiber-optic networks in which light waves transport information at rates of gigabits
per second through optical fibers finer than the human hair.
The stakes are very high. In a May 2000 news release, The Aberdeen Group (Boston, MA), an IT
consulting firm, predicted that "The optical network market, excluding SONET elements, will grow to
$17.7 billion by 2003. The suppliers that can deliver the technologies that solve the problems that
carriers face, will be the ones to succeed."
The use of the plural in "suppliers" and "technologies" highlights a key issue in this article. The
burgeoning communications network is highly complex. While a few large companies tend to dominate
the global deployment of the optical network, behind the scenes there is a fusion of technologies
developed by multiple companies, each with specialized technological expertise. Maxim falls into this
latter category; we have designed a family of variable resistors especially for optical transceiver modules.
A look at where Maxim's resistors fit into the grand scheme of communications networks reveals
something about the way the communications industry develops solutions.
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