More specifically,
”The principle of sigma-delta modulation, although widely used nowadays, was de- veloped over a time span of more than 25 years. Initially the concept of oversam- pling and noise shaping was not known and the search for an efficient technique for transmitting voice signals digitally resulted in the Delta Modulator. Delta modula- tion was independently invented at the ITT Laboratories by Deloraine et al. [11, 12] the Philips Research Laboratories by de Jager [10], and at Bell Telephone Labs [8] by Cutler. In 1954 the concept of oversampling and noise shaping was introduced and patented by Cutler [9]. His objective was not to reduce the data rate of the signal to transmit as in earlier published work, but to achieve a higher signal-to-noise ratio in a limited frequency band. All the elements of modern sigma-delta modulation are present in his invention, except for the digital decimation filter required for ob- taining a Nyquist rate signal. The name Delta-Sigma Modulator (DSM) was finally introduced in 1962 by Inose et al. [25, 26] in their papers discussing 1-bit converters. By 1969 the realization of a digital decimation filter was feasible and described in a publication by Goodman [16]. In 1974 Candy published the first complete multi-bit Sigma-Delta Modulator (SDM) in [6]. Around the same time the name SDM was introduced as an alternative for Delta-Sigma Modulator and since then both names are in use. In this book the oversampled noise-shaping structure will be referred to as SDM. According to the author SDM is the more appropriate name since the integration or summing (the sigma) is over the difference (the delta).”
”The principle of sigma-delta modulation, although widely used nowadays, was de- veloped over a time span of more than 25 years. Initially the concept of oversam- pling and noise shaping was not known and the search for an efficient technique for transmitting voice signals digitally resulted in the Delta Modulator. Delta modula- tion was independently invented at the ITT Laboratories by Deloraine et al. [11, 12] the Philips Research Laboratories by de Jager [10], and at Bell Telephone Labs [8] by Cutler. In 1954 the concept of oversampling and noise shaping was introduced and patented by Cutler [9]. His objective was not to reduce the data rate of the signal to transmit as in earlier published work, but to achieve a higher signal-to-noise ratio in a limited frequency band. All the elements of modern sigma-delta modulation are present in his invention, except for the digital decimation filter required for ob- taining a Nyquist rate signal. The name Delta-Sigma Modulator (DSM) was finally introduced in 1962 by Inose et al. [25, 26] in their papers discussing 1-bit converters. By 1969 the realization of a digital decimation filter was feasible and described in a publication by Goodman [16]. In 1974 Candy published the first complete multi-bit Sigma-Delta Modulator (SDM) in [6]. Around the same time the name SDM was introduced as an alternative for Delta-Sigma Modulator and since then both names are in use. In this book the oversampled noise-shaping structure will be referred to as SDM. According to the author SDM is the more appropriate name since the integration or summing (the sigma) is over the difference (the delta).”