11b/14b Encoding – A Fault Tolerant, DC-Balanced Line Code for AC-Coupled Channel Link Transceivers

摘要

This paper presents a fault tolerant, DC-balanced line encoding scheme for use with AC-coupled Channel Link transceivers which feature 7-bit frame alignment as opposed to a more typical 8-bit alignment. Channel Link is a popular high-speed interface for aerospace applications (such as image streaming via Camera Link), popularized by Cobham-Aeroflex's radiation tolerant UT54LVDS217/8 3-lane serializer/deserializer buffer pair which is capable of 1.575 Gbps of throughput. Use of Channel Link transceivers in AC-coupled link topologies imposes stringent requirements on the runlength (maximum sequence of repetitive ‘1's or ‘0's) and running disparity (difference between total number of ‘1's and ‘0's) of the transmitted line encoded data. Existing line encoding schemes such as 8b/10b meet these requirements, however, none of them support a 7-bit aligned data frame that is imposed by Channel Link. We present a line encoding scheme that is an extension of 8b/10b encoding theory, including an adaptation of optional control (comma) codes, that supports the mapping of 11-bits of unencoded data into two 7-bit aligned encoded data frames in support of AC-coupled Channel Link interconnects. Functional verification of the encoding scheme is demonstrated through rigorous simulation and hardware prototyping featuring a UT54LVDS217 transmitter AC-coupled into a Microsemi RTG4's built-in SERDES receiver.