By Charles L. Wingate
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Integrating magnetic components into an RJ-45 connector frees up board space and offers signal protection.
R J-45 connectors integrated with magnetic components have emerged as one of the hottest components for communications and networking input/output (I/O) applications because they are helping manufacturers reach their goals of cost reduction, improved reliability and optimal system performance. Personal computer equipment makers were the first to integrate magnetics into their Ethernet port connectors. By reducing the number of components to be placed on the board, they enjoyed assembly cost savings and gained board space. Communication and networking equipment makers also saw the benefits of having shorter signal paths and the reliability gains from systems containing fewer components. They and manufacturers of set-top boxes have also standardized on RJ-45 connectors integrated with magnetic components in order to meet FCC emissions requirements at higher speeds.
As the Internet has fanned demand for hubs, routers, switches and network interface cards (NICs) to enable computers everywhere to network with each other, wiring closets, desktops and data centers have become more crowded with electronic equipment, which puts space at a premium. Sophisticated software applications demand higher system performance, which entails faster signal speeds and higher bandwidth to carry the information. As speeds increase, the signals become more vulnerable to distortion from crosstalk, electromagnetic interference (EMI) and radio frequency interference (RFI). But at the same time, the proliferation of equipment generates more "noise," more cables and more sources of interference. Because market competition is forcing system manufacturers to drive costs down and to provide hassle-free system reliability, traditional design assumptions must be revisited from the system level to the component level.
In a high-speed, high-frequency environment, one of the weakest links is not in the system itself but in the cables and connectors that tie the system to the rest of the world. Cables and connectors can compromise the integrity of shielded enclosures by acting as antennas — both broadcasting and absorbing EMI and RFI. They, along with the electronics residing at either end of a cable, play a key role in overall system performance.
Typical Systems
In a typical system with a network interface, one finds an I/O connector, magnetic components, termination networks on both the media and transceiver side of the interface module, decoupling capacitors and a transceiver chip. The magnetic components, including chokes, isolation transformers, filters, resistor networks and high-voltage capacitors, perform a variety of signal-conditioning functions. Although as separate components on a board these items can consume a square inch of board real estate per connector port, they are very necessary. Incoming signals carried on a cable often pick up noise or EMI from adjacent cables, electronic hardware, electric motors, motor vehicles and a host of other sources.
To preserve system performance, chokes and filters are used to separate the real signal from the extraneous noise. Transformers are then used to provide matching and filtering and to isolate the network and physical layer transceiver. Capacitors are used to protect against damage caused by high voltages that may be carried into the system by network cables. Line-to-chassis resistor networks, when matched to the line, improve EMI performance.
Integrated Connectors
A connector integrated with magnetic components allows system designers to protect signals and reduce the number of components on the board by integrating all of this functionality into the connector. From the outside, the connector itself is mechanically no different from passive RJ-45 connectors; it takes up the same amount of board space. All of the additional functionality is packed on small modules or printed circuit boards inside the connector. The transceiver chip can now be moved right up against the connector, minimizing the signal path between the transceiver chip and the connector. Components that previously generated noise themselves and were affected by noise from other components within the system are no longer there. Now, they are protected by the connector's own shield.
Noise Reduction
Noise reduction in the system is an immediate benefit. High noise levels pose problems for digital and analog signals passing through the system. In today's high-speed systems, signals must remain precise and uncorrupted. Cables pick up EMI and carry it into the system. In conventional designs, the EMI makes it onto the board before it is filtered out. This incoming noise then has a chance to radiate from board traces and interfere with other components on the board. Even board traces between signal-conditioning components can become sources of noise. With the filters inside the connector, the EMI is cleaned before it ever reaches the board. Less noise on the board means better system performance. According to Mohammad Saboori, electrical engineering manager, InNet Technologies (San Diego), noise reductions of up to 20 dB have been measured by putting the magnetic components inside the connector.
 Figure 1. Integrated magnetic components can significantly increase the amount of available board space. |
Similarly, there is a gain in system performance and a reduction in noise on outgoing signals by placing the transceiver chip right next to the connector. This means that the signals travel a much shorter distance from the transceiver chip and that the signals are filtered at the connector just before they leave the system. Signals traveling shorter distances are less prone to EMI from other system components, and even if they are affected, they are filtered at the last possible instance.
Integrating magnetic components into a connector affords greater reliability for the components themselves as well as the system they are in. In general, discrete magnetic components are known as some of the least reliable components within a network or communications circuit. This is because they are full of very fine wires and delicate solder joints that are subject to breakage through shock, vibration and thermal cycling, which they encounter during the production processes.
Placing magnetic components into the connector can provide robust solder joints within the components themselves because there is more space inside the connector than in a conventional magnetics package. Integrating the magnetic components also reduces the number of solder joints. All of these factors combine to give the magnetic components and the entire system better reliability.
Integrating magnetic components into connectors also pays dividends through design simplicity. As the number of components on the board is reduced and the corresponding number of traces is also reduced, the sheer number of components on the board is less. This means fewer parts to be placed on the board, fewer parts to be stocked in the warehouse and less cost to manage it all.
Conclusion
Today, most applications designed to use RJ-45 connectors with integrated magnetic components involve custom designs of magnetics specifically tailored to each system. There are no industry standard footprints, although some suppliers have promised to second source each other. All of this should change as more and more products come into the market. RJ-11 connectors are not yet available with integrated magnetic components, but with the proliferation of digital subscriber line (DSL) and voice-over-Internet protocol (IP) applications, it is only a matter of time until they become a reality.
The benefits of integrated magnetic components are clear. As the communications and networking industries move toward smaller, more powerful and efficient systems and devices, system designers must look to new technologies and techniques that better satisfy the needs of cutting-edge applications. Integration of functions on the board is a logical and necessary step. Reducing the distance that signals travel makes them less vulnerable to distortions from system-generated and externally generated noise. Putting the signal conditioning inside the metal shielding of the connector protects this functionality in both incoming and outgoing directions.
Anything that enables higher system performance, reduces costs, simplifies designs and shrinks the size of the unit has to be good. That is why manufacturers of computers, networking equipment, telecommunications equipment, set-top boxes and other communications devices are designing around RJ-45 connectors with integrated magnetic components. That is also why so many manufacturers of connectors and magnetics are tooling or looking into tooling these types of products.
CHARLES L. WINGATE is vice president, Sales and Marketing, Stewart Connector Systems Inc., Insilco Technologies Group, 11118 Susquehanna Trail, South Glen Rock, PA 17327-9199; (717) 235-7512; Fax: (717) 235-8414; E-mail: cwingate@stwconn.com; Web site: www.stewartconnector.com.
SPEC SHEET
End Applications: Networking and communications equipment, computers, set-top boxes
Related Products: RJ-45 connectors, cables, PCBs
Main Point: As the communications and networking industries move toward smaller, more powerful and efficient systems and devices, system designers must look to new technologies that better satisfy the needs of cutting-edge applications. Integration of functions on the board is a logical and necessary step.
Integrating magnetic components into an RJ-45 connector saves board space and provides signal protection. This, in turn, enables better system performance, increases reliability and lowers costs.
