Fixed-step simulation of Continuous-Time ΣΔ modulators

A methodology for the simulation of continuous time sigma-delta (CTSigmaDelta) converters is presented in this paper. This method permits the simulation of SigmaDelta modulators employing continuous-time filters using a fixed-step algorithm. 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, each sampling- period is divided into a fixed number of steps. This transformation is exact in term of Noise Transfer Function and asymptotically exact in term of Signal Transfer Function (the Signal Transfer Function of the model rapidly tends to the continuous time model transfer function when the number of steps increases). Moreover, the ideal step-size can be estimated from the bandwidth of the input signal.