Signal processing in the sigma-delta domain

Abstract

Sigma-delta (ΣΔ) has been widely used to convert signals between analogue and digital [1]. Some authors propose the extension of this technique to implement analogue and digital filters, amplitude and phase modulators, correlators, adders, compandors, expandors, digital synthesizers, oscillators, phase-locked loops and frequency discriminators, power drivers, etc. This paper is in line with these non-standard applications, and proposes that ΣΔ be seen as a complementary domain for signal processing in parallel with continuous-time (CT), sampled-data (SD) and digital (D). The interface blocks are introduced, as well as the operators available for either sigma-delta or mixed signal processing. Sigma-delta signals are easy to handle, but have reduced processing capabilities. Mixed processing is possible without requiring interface circuitry and with significant savings in algorithms and hardware. Design examples of sigma-delta adder, multiplier, compandor, expandor, automatic gain control, direct digital synthesizer, oscillator and phase-locked loop circuits are given.