Characterization and modeling of cables for high-speed data communications applications

Designers of data communications systems continue to push the limits of copper cable to achieve higher speeds and longer cable lengths. At the same time, shortened product schedules due to competition often prevent the use of prototyping in early system architecture. These developments mandate the use of simulation in early system feasibility and design. Simulation has been used in the design of VLSI ICs for many years, and has been adopted at the card and board level in recent years as the speed of digital systems increases. However, modeling of cables has not been widespread due to the difficulty in obtaining the physical data necessary for the task, as well as the inadequacy of many simulators to properly simulate the skin and other effects encountered when using cables in high-speed systems. This paper will present hardware measurement data for some types of shielded parallel and twisted pair cable typically used for the interconnection of high-speed digital systems, and outline some of the problems encountered in the electrical characterization and modeling of those cables. Selected simulation models will be presented, with comparisons of the measured and simulated results obtained using those models