Synthesis and Analysis of Sigma-Delta Modulators Employing Continuous-Time Filters

A methodology for analysis and synthesis of lowpass sigma-delta (ΣΔ) converters is presented in this paper. This method permits the synthesis of ΣΔ modulators employing continuous-time filters from discrete-time topologies. The analysis method is based on the discretization of a continuous-time model and using a discrete simulator, which is more efficient than an analog simulator. In our analysis approach, the influence of the sample and hold block and non-idealities of the feedback DAC can be systematically modeled by discrete-time systems. Finally, a realistic design of a second-order ΣΔ modulator with a compensation of the non-ideal behavior of the DAC is given. Moreover, simulation results show a good agreement with the theoretical predictions.

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