SAMPLED-DATA SIMULATION OF OVER-SAMPLED SIGMA-DELTA MODULATORS - Computer Methods for Analysis of Mixed-Mode Switching Circuits - page 190

1. Introduction
Over-sampled sigma-delta modulators are widely encountered in analog-
to-digital data conversion[72]. These modulators trade off speed for ac-
curacy, and can achieve a high precision resolution without requiring
precisely matched analog components. In addition, they can be fabri-
cated on the same substrate with other digital circuitry using standard
digital fabrication technologies. A typical configuration of a clocked first-
order over-sampled sigma-delta modulator is shown in Fig.9.1. The key
element of over-sampled sigma-delta modulators is the quantizers, imple-
mented using comparators with one input from the output of the integra-
tor and the other the ground, that quantizes the incoming analog signal
and outputs a stream of digital data. These serial digital data stream
is then converted to parallel data using a decimator. The main function
of the integrator in the forward path is to sense the difference between
the incoming analog signal and the output of digital-to-analog converter
and drive the difference to zero in an integrating manner. Single-bit
oversampled sigma-delta modulators are the most widely used, owing to
their intrinsic advantages of the ease in implementation and insensitivity
to non-idealities of integrators.