Oversampling and sigma-delta strategies for data conversion

This paper presents an introduction to oversampling techniques and the theory and advantages of sigma-delta (ΣΔ) devices for digital-to-analogue conversion (DAC) and analogue-to-digital conversion (ADC) in digital signal processing (DSP) systems. It begins with a discussion of conventional Nyquist-sampling-rate DSP, which is followed by an overview of oversampling and decimation/interpolation techniques to reduce the anti-alias and reconstruction filter specifications. Oversampling strategies to increase the resolution of an N-bit ADC or DAC by reducing the baseband quantisation noise are then presented, and this is followed by a description of the use of ΣΔ noise-shaping techniques and the design of ΣΔ converters. The paper concludes with comments on a few of the application and research areas where ΣΔ devices are having a major impact