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

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.