TABLE OF CONTENTS Before physical signals can be processed digitally they have to be converted from the analog to the digital form, by means of an analog-to-digital (A/D) converter. Unfortunately this conversion introduces distortion. The stringent requirements, which the modern market imposes on A/D conversion, became achievable only due to the advent of fast and complex integrated circuits. There is a growing demand of more than 13-bit A/D converters which can not be designed solely in analog as the required component matching for a large number of bits is extremely difficult to achieve and sustain. One of the many alternative choices is presented here that allows achieving very high bit lengths: A/D conversion via the intermediate stage of 1-bit coding, at a very high sampling rate [11]. One-bit coding is achieved by a Sigma-Delta ( ? ?) modulator stage, which is then followed by a decimator in which the sampling rate is decreased and the magnitude resolution is increased. This architecture primarily covers audio band applications and is especially attractive for VLSI implementation.
In this section we first look at the requirements to be met by the Nyquist and the oversampling A/D converters in digital signal processing applications and the arguments in view of the intermediate stage 1-bit coding. Then the typical ? ? modulator is presented. The quantization noise shaping by the ? ? modulators and the effects of the noise on the resolution of the A/D converter are also presented.
