Differential Signaling with a Reduced Number of Signal Paths

Differential signaling is often used for digital chip-to-chip interconnects because it provides common-mode noise rejection. Unfortunately, differential signals generally require 2 signal paths to communicate signals. In this paper, a method for differential signaling is described that requires as few as +1 signal paths for signals. Using this method, the signal values appear incrementally between neighboring matched signal paths. The technique, called incremental signaling, is similar to dicode (1 ) partial response signaling except that the sequence is transmitted in parallel over a bus of wires rather than sequentially in time. Theoretical and simulated bit error rates are presented for several possible implementations of an encoder/transmitter and receiver/decoder for a digital data bus including peak detection and maximum likelihood sequence detection (MLSD). Peak detection uses +1 signal paths and results in a 3-dB performance degradation with respect to independent noise compared with fully differential signaling. The Viterbi algorithm for MLSD uses +2 signal paths but provides only a 1.25 dB improvement over peak detection due to correlated noise on the (1 )-coded sequence. Modified Viterbi algorithms that use +2 signal paths are introduced to cancel the correlated noise sources, resulting in a bit error rate performance comparable with fully differential signaling.