Theory and applications of incremental ΔΣ converters

Analog-Digital (A/D) converters used in instrumentation and measurements often require high absolute accuracy, including very high linearity and negligible dc offset. The realization of high-resolution Nyquist-rate converters becomes very expensive when the resolution exceeds 16 bits. The conventional delta-sigma (ΔΣ) structures used in telecommunication and audio applications usually cannot satisfy the requirements of high absolute accuracy and very small offset. The incremental (or integrating) converter provides a solution for such measurement applications, as it has most advantages of the ΔΣ converter, yet is capable of offset-free and accurate conversion. In this paper, theoretical and practical aspects of higher order incremental converters are discussed. The operating principles, topologies, specialized digital filter design methods, and circuit level issues are all addressed. It is shown how speed, resolution, and A/D complexity can be optimized for a given design, and how with some special digital filters improved speed/resolution ratio can be achieved. The theoretical results are verified by showing design examples and simulation results.