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Magnetic developments must keep pace with the DSL market

Posted: 28 Feb 2002 ?? ?Print Version ?Bookmark and Share

Keywords:dsl chips? magnetic components? chokes? isolation transformers? filters?

A number of techniques are being employed in magnetic-component manufacturing to meet small-size, low-power and low-cost DSL modem needs, observes Terry Van Conant.

Terry Van Conant is the marketing director of the CoEv division of Tyco Electronics Corp.
Digital subscriber line (DSL) modem makers are rapidly developing easy to use plug-and-play customer-premise equipment (CPE) and computer preinstalled devices. They also are providing inexpensive customer-installable microfilters that eliminate the need for technician-installed splitters, thereby facilitating more rapid deployment of ADSL modems.

While IC makers are busy churning out higher-functionality and lower-power-dissipation IC chipsets 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 signal-conditioning functions. So reducing their size and count, 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 PCB 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 instance, 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 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 into small modules or PCBs inside the connector. The connector's metal shielding protects components that generate noise, or may be affected by noise from other components within the system.

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.

? Terry Van Conant

Marketing Director, CoEv Division

Tyco Electronics Corp.

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