An Overhead-Reduced Key Coding Technique for High-Speed Serial Interface

This paper describes a packet-based overhead-reduced (OR) key coding technique for a high-speed serial interface. The 8B10B code is a de facto standard coding technique in the application but its bit-overhead is 25%. The proposed key coding technique is to reduce the coding overhead and still provides enough bit transition to facilitate clock and data recovery in the receiver. After a key pattern is generated from a certain data stream, input data are encoded and framed as packets along with the generated key for transmission. The packets are transmitted and then decoded as original data in the receiver. Using the proposed coding scheme, 4-, 6-, and 8-bit key coding systems are designed and compared. When a 6-bit key coding encoder/decoder is tested, a packet is composed of a 6-bit OR key header followed by 30 encoded sub-packets, in which each sub-packet has a 6-bit data. In the 6-bit case, the bit overhead is only 3.33% and the maximum continuous run length is 10 bits. To control the running disparity for the AC coupling interface, a logic for selecting the optimal key is implemented to keep the running disparity as low as possible. The running disparity of the encoded data with 6-bit key code is controlled within +/−12.