Adaptive Delta Modulation for Companded PCM Coding and Decoding

An adaptive delta modulator and demodulator are used as the first and last stages in a system for coding and decoding telephone signals into μ = 255 companded pulse code modulation (PCM). The system objectives are to devise an economic coder and decoder that is reliable, free of potentiometer adjustments, and convenient for automated manufacturing for large quantity production. The strategy is a shift of circuit emphasis from analog to digital in order to take full advantage of low-cost, low-speed digital processing technology such as MOS/LSI to achieve the desired objectives. The system structure, digital signal processing, system implementation, and performance of the prototype are discussed in this paper.