Spectral characteristics of the double loop ΣΔ modulator

An important factor affecting the performance of ΣΔ 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