Attractive line codes for high-speed LANs and MANs and their realization

Steadily increasing data rates in local and metropolitan area networks call for the high-speed realization of line codes. For many applications these line codes should be DC-free. The code selected for the fiber channel standard (FCS) belongs to a class of DC-free codes known as alternate codes. New DC-free line codes that improve the timing properties of the FCS code are constructed. Look-ahead precomputation and state switching are used to reduce single XOR operation. A high-speed encoder architecture for two-state alternate codes, based on state switching and parallel processing, is described, using the example of the FCS code. The architecture is well-suited to VLSI implementation. Using this architecture, the FCS code can be efficiently realized with a low-speed technology (e.g., CMOS) even at multigigabit data rates