ΣΔ A/D conversion

A first patent related to delta modulation was filed in 1948 [21]. In 1952, the delta modulator was first published by de Jager and Greefkes at the Philips Research Laboratories (fig. 3.1, [22]). The invention was inspired by the operation of the human brain: physiological signals are translated into a series of electrical pulses in the nerve system as a means for data transmission to the brain. In a similar way, pulse density modulation was used for robust data transmission in telephony. In the single-bit, delta-modulated code all bits are of equal weight and any bit-flip causes only a small error. In a multi-level PCM code though a bit-flip of the Most-Significant-Bit results in a major error. The paper by de Jager in 1952 [22], on delta modulators was the first in a massive series of delta-sigma and sigma-delta papers. In 1960, the delta-sigma modulator was patented by Cutler [23]. Inose et al. [24] proposed to shift the loop filter in the forward path of the modulator in 1962. In the 1980’s sigma-delta conversion became popular in both the A/D and the D/A part of audio channels. In addition, instrumentation applications widely adopted ΣΔ converters. By that time, a lot of theoretical work had been published, a.o by J. Candy.