Delta Modulation Codec for Telephone Transmission and Switching Applications

Delta modulation 1 (AM) is receiving interest for voiceband analogto-digital (A/D) conversion applications where coding efficiency is less important than the requirement for economical, but high quality A / D conversion, characteristics. One of the potential applications is in pulse code modulation (PCM) coding systems where the P C M code is formed by first converting the analog signals into a single bit digital code using per terminal AM coders. The AM bit stream is then converted into a P C M format using digital filtering. 2 , 3 The technique takes advantage of the simple means of providing A / D conversion with AM and utilizes highly integrable digital hardware for providing the AM to P C M conversion. Another promising application of AM is in space division switching networks. Analog inputs to the network are converted into a digital code by per terminal AM coders. This allows implementation of digital switching networks which are more ideally suited to integrated semiconductor technology than analog networks. Requirements on network loss, signal distortion and crosstalk are significantly relieved. We describe the design of a single integration AM codec (coderdecoder) which shows promise of meeting the conversion requirements for both of the above applications. Improved conversion characteristics 1013