Feedback Balanced Code for Multilevel PCM Transmission

This paper describes a new code format called the feedback balanced code (FBC) for multilevel pulse code modulation (PCM) transmission, which is easily implemented and is capable of efficient utilization of transmission cable. The FBC is a type of multilevel code which has no dc wander and is obtained by the polarity control of the output pulse sequence using negative feedback. The principle of the FBC and its static balance condition are discussed, and spectral analysis using transition probability is described. FBCs are shown to have spectral nulls at dc and at frequency f
o
. Suppression of the low-frequency component is also represented by a transfer function of the FBC converter by employing an appropriate assumption of linearization. The suppression characteristic is much improved by using a double integration feedback network. A higher order FBC is also discussed, which has spectral nulls at frequency
f_{o}/n
and its integral multiples. The preceding theoretic approach was well verified through experiments.