Electronic Design

Magnetic Developments Must Keep Pace With An Explosive DSL Market

By now, we should all be familiar with the explosive growth in digital subscriber line (DSL) technology. Estimates are that cable-modem and DSL subscriptions will rise 77% annually between 1999 and 2004, and revenues will grow from $1 billion to $13.3 billion over the same time frame.

DSL modem manufacturers are rapidly developing easy to use plug-and-play customer-premise equipment (CPE) and computer preinstalled DSL modems. They also are providing inexpensive customer-installable microfilters that eliminate the need for technician-installed splitters, thereby facilitating more rapid deployment of asynchronous DSL (ADSL) devices.

While IC makers are busy churning out higher-functionality and lower-power-dissipation IC chip sets for DSL modems, the more fundamental magnetic components of chokes, isolation transformers, and filters are being forced to keep equal pace with IC advances to satisfy DSL modem needs.

In a typical high-speed network interface, a number of magnetic components might perform a variety of signal-conditioning functions. Reducing their size and their numbers while improving their reliability is becoming a very challenging endeavor. In response to this, a number of techniques are being employed in magnetic-component manufacturing to meet small-size, low-power, and low-cost DSL modem needs. Size reduction through form-factor changes, modularization, and integrating the magnetics with connectors are the three principal techniques.

Modularizing board-level magnetics simplifies PC-board design and reduces component count and the corresponding number of traces. By installing some of the line-conditioning components on a piggyback board, the main board can be used exclusively for the ICs and value-added functionality. Additionally, this approach to signal protection improves reliability and reduces system temperature.

The approach of placing some signal and circuit-protection devices outside the footprint of the modem satisfies many of the emerging requirements and provides additional benefits. For example, integrating magnetic components with RJ-45 connectors and overcurrent and overvoltage protectors reduces component count on-board, minimizes the signal path between the transceiver chip and the connector, and effectively reduces noise. Some manufacturers, including CoEv, also are developing integrated analog front-end solutions for DSL technologies.

As signals get faster, they become more vulnerable to crosstalk, EMI, and RFI, with cables and connectors acting as antennas, both broadcasting and absorbing noise. Integrating the magnetics and the connector places the entire signal-conditioning functionality in small modules or PC boards inside the connector. Components that generate noise, or may be affected by noise from other components within the system, are protected by the connector's metal shielding.

Reducing the distance that signals travel also makes them less vulnerable to distortion. Placing the transceiver chip next to the connector filters signals before they leave the system. Signals traveling shorter distances are less vulnerable to EMI from other components too. Aside from more available board space provided by this solution, there are significant reliability gains from having fewer components.

Keeping pace with the demand for smaller, faster, more-powerful systems, magnetic-component manufacturers are working with suppliers and OEM customers to develop devices that enhance modem performance, improve reliability, simplify design, and reduce costs.

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