Designing CT ΣΔ modulators with shaped feedback waveforms using www.sigma-delta.de

This paper describes an automated design approach to obtain continuous-time ΣΔ modulators with non-rectangular and even multiple DAC feedback waveforms using www.sigma-delta.de. There already exist well known techniques to calculate the necessary high-level coefficients for DAC waveforms other than non-return-to-zero. However, these calculations require expert understanding of ΣΔ modulators and get more challenging if two or even more different waveforms are utilized within one modulator. The design approach proposed in this paper allows an easy-to-use integration of multiple feedback waveforms in a rapid design process without further calculations and sophisticated knowledge on system theory or modulator design. This work presents the capabilities of the freely available design tool with regard to DAC waveforms and gives corresponding examples. Moreover, to emphasize the different characteristics of the individual waveforms, the sensitivity to ELD variations of all modulators is shown.