Introduction to Modulators: Basic Concepts and Fundamentals

This chapter is conceived as an introduction to CMOS Sigma-Delta (?>?>) analog-to-digital converters (ADCs). Their operation principle consists in combining oversampling, quantization error processing, and negative feedback for improving the effective resolution of a coarse quantizer. Before presenting practical topologies for the implementation of ?>?> modulation, the large variety of the existing ?>?> realizations is briefly classified according to the type of modulator architecture (single loops or cascades), the circuit techniques employed (discrete time (DT) or continuous-time (CT)), and the nature of the signals being converted (low pass (LP) or band pass (BP)). Starting from the case of DT, LP, single-bit ?>?> modulators, the implications of these different alternatives are then presented in an incremental way.