Introduction

Abstract

Analog-to-digital (A/D) conversion and digital-to-analog (D/A) conversion lie at the heart of most modern signal processing systems where digital circuitry performs the bulk of the complex signal manipulation. As digital signal processing (DSP) integrated circuits become increasingly sophisticated and attain higher operating speeds more processing functions are performed in the digital domain. Driven by the enhanced capability of DSP circuits, A/D converters (ADCs) must operate at ever-increasing frequencies while maintaining accuracy previously obtainable at only moderate speeds. This trend has several motivations and poses important consequences for analog circuit design. The motivations for processing most signals digitally are manifold: digital circuits are much less expensive to design, test, and manufacture than their analog counterparts; many signal processing operations are more easily performed digitally; digital implementations offer flexibility through programmability; and digital circuitry exhibits superior dynamic range, thereby better preserving signal fidelity. As a consequence of the aforementioned advantages accrued by DSP, fewer and fewer operations benefit from analog solutions. Since A/D conversion generally requires more power and circuit complexity than D/A conversion to achieve a given speed and resolution, ADCs frequently limit performance in signal processing systems. This fact underscores the second consequence of enhanced DSP performance on the role of analog circuit design. That is, since A/D conversion limits overall system performance, development of improved A/D conversion algorithms and circuitry represents an extremely important area of research for the foreseeable future.