Line Coding Methods for High Speed Serial Links

摘要

A line coding for high speed serial transmission is defined by two major characteristics: the maximum guaranteed run length (RL) which is the number of consecutive identical bits, and the running disparity (RD or DC-Balance) which is the difference between the number of 'zeroes' and 'ones' in a frame. Both should be bounded to a certain limit, RL to ensure reliable clock recovery and RD to limit baseline wander. Another important parameter is the overhead predictability. This parameter could be critical for applications that need a regular synchronization but for other application, especially if variable transfer rate is handled by the upper layer protocol, a statistical value of this parameter is good enough. In this paper, we propose two programmable line codings which bound RL and RD with fix or variable overhead. The resulting overhead for the line coding we propose shows to be the lowest between the existing methods, down to 10 times lower than famous encoding methods. The fix overhead line coding is based on a generalization of the polarity bit approach and could be dynamically adapted to link quality and environment. First we propose a line coding which bounds the RL, and then we propose another one which bounds the RD. We end up by combining both methods to build a DC-balanced and Run Length limited line coding.