Optimum Digital Filters for Interpolative A/D Converters

Interpolative A/D converters 1-3 achieve a fine quantization of signals by making several coarse quantizations and averaging them. This requires high-speed operation of that part of the A/D converter which obtains the coarse quantizations. Higher and higher speeds are required for finer and finer ultimate quantization. This trade-off between the speed of operation and amplitude resolution is particularly relevant and important with present-day integrated circuit technology, which provides high-speed operation but no high-amplitude precision. Several well known methods of obtaining the many coarse quantizations exist. Goodman, 1 and Goodman and Greenstein, 2 have considered the ordinary delta modulator which gives a two-level representation of the signal at a rate many times higher than the Nyquist rate. The output of the delta modulator is filtered by a digital filter and resampled at 1629 ANALOG INPUT elf) SLOW RESAMPLER ANALOG FILTER *(f) Wis) QUANTIZER DIGITAL FILTER DU) DIGITAL OUTPUT