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Line coding methods for high speed serial links

Auteur(s) : A. Goulahsen, J. Saade, F. Pétrot

Doc. Source: International Symposium on Microelectronics (IMS'15)

Publisher : IMAPS Int. Microelectron. & Packaging Soc.

Pages : 318-323

Doi : 10.4071/isom-2015-WA63

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 may be critical for applications that need a regular synchronization but for other applications, especially if the 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 fixed or variable overhead. The resulting overhead for the line coding we propose is shown to be the lowest among the existing methods, as much as to 10 times lower than well-known encoding methods. The fixed overhead line coding is based on a generalization of the polarity bit approach and can be dynamically adapted to link quality and the 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.