STF engineering in CT sigma-delta modulators using www.sigma-delta.de

This paper presents a straightforward method of STF engineering in continuous-time ΣΔ modulators within the web-based design tool www.sigma-delta.de. There are already different well known methods to obtain the STF depending on constraints given by the designer. One possibility is the analytical derivation of the high-level coefficients yielding a certain STF. Further, the ΣΔ modulator can be embedded into a filter with the desired characteristic or vice versa. However, as the NTF and STF are dependent upon each other, they cannot be chosen independently. The web-based design tool for continuous-time ΣΔ modulators relies on a heuristic search based on a genetic algorithm that is able to determine a STF complying to given constraints while maximizing the signal-to-noise ratio of the chosen modulator architecture at the same time. This paper shows the capabilities of the publicly available design tool in regard of STF engineering and gives corresponding examples.