Spectral Characteristics Of The Double Loop \Sigma\Delta Modulator

Abstract

An important factor affecting the performance of \Sigma\Delta modulators is their tone behavior. A recent approach to alleviate the tone problem consists of moving the open loop poles outside the unit circle. In this paper, we determine the frequency location of two dominant tones as a function of pole location and obtain a partial characterization of the spectral shape. Audio testing along with a series of simulations are then performed to compare the efficacy of pole placement with that of the more traditional tone removal technique of dithering. 1 INTRODUCTION Sigma delta (\Sigma\Delta) modulators are becoming increasingly important in data conversion applications. An important factor limiting the performance of \Sigma\Delta modulators is their tone behavior [1, 2]. Repeating patterns at the output of \Sigma\Delta modulators result in spectral peaks or tones in the output spectrum. Tones are especially objectionable in audio applications since their presence in the signal baseband..