This chapter presents a theoretical overview of analog to digital conversion using Sigma-Delta Modulation (ΣΔM). Its oversampling characteristic and working principles are explained and compared with Nyquist rate converters. Important performance parameters, such as signal to noise ratio (SNR), effective number of bits (ENOB), and oversampling ratio (OSR), are also presented. The typical topology of first and second order ΣΔ modulators is studied in the time and frequency domain, from which the modulators’ signal (STF) and noise (NTF) transfer functions are obtained, along with the noise shaping property inherent in ΣΔ modulation. Lastly, the stability problems associated with higher order ΣΔ modulators are addressed and the MASH structure is presented as a solution to such problems.
KeywordsSigma-delta modulation Analog to digital conversion Oversampling Nyquist rate Signal to noise ratio Effective number of bits Oversampling ratio Noise shaping Multi stage noise shaping
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