Extending the useful range of copper interconnects for high data rate signal transmission

As data processing speeds increase, systems designers are continually bumping into the limitations of traditional wiring methods and become tempted to cross the barrier into fiber optics technology. Several techniques for increasing the useful range of copper based interconnects in both bandwidth and distance have been developed. These can lead to cost effective alternatives to implementing fiber optic solutions, especially for distances up to 100 meters. Critical to maximizing the benefits of these techniques is to take a system approach which goes beyond just improving cable or connector design. This paper discusses the typical challenges facing interconnect designers along with potential solutions that can be generally applied to a variety of applications. Improvements in cabling technology are shown including reduced skew, tightened impedance control, higher density designs, multi-signal termination techniques and built-in equalization. Suitable connector types are also presented to evaluate compatibility and availability. System considerations such as parallel vs. serial, driver and receiver types, selection of characteristic impedance and encoding schemes are included for further background on design issues. All of this information is presented in light of typical concerns such as signal fidelity, cable size, EMC, and cost. Tradeoffs between copper and fiber optic based systems are presented based on current and expected future costs. As the need for a fiber optic link becomes more evident, a seamless migration approach is outlined which allows fiber optic links to be selectively installed on an as needed basis for longer distance runs.