Building Blocks for SI Oversampling A/D Converters

Abstract

As discussed in Chapter IV, we need integrators, differentiators, current quantizers, and 1-bit D/A converters to construct SI delta-sigma modulators. To control SI delta-sigma modulators, clock generators are needed. In some applications, the input analog signal is a voltage signal, a voltage-to-current (V/I) converter is usually needed before driving an SI oversampling delta-sigma modulator. Due to the advantage of oversampling, a simple low pass filter sometimes suffices as the anti-aliasing filter for oversampling A/D converters. It is of interest to integrate such a filter in the digital CMOS process. To convert the output of an SI delta-sigma modulator into a more convenient digital representation, a digital decimation filter is needed to remove the high-frequency noise and reduce the sampling rate. To open switches for 1.2-V SI circuits, voltage doublers are needed. To collect the output data of a low-voltage oversampling A/D converters into a computer, an on-chip level conversion is also needed. In this chapter, we will discuss all these building blocks.