A behavioral simulation tool for continuous-time ΔΣ modulators

Circuit-level simulation of ΔΣ modulators is a time-consuming task (taking one or more days for meaningful results). While there are a great variety of techniques and tools that speed up the simulations for discrete-time (DT) ΔΣ modulators, there is no rigorous methodology implemented in a tool to efficiently simulate and design the continuous-time (CT) counterpart. Yet, in todays low-power, high-accuracy and/or very high-speed demands for A-to-D converters, designers are often forced to resort to the use of CT ΔΣ topologies. In this paper, we present a method for the high-level simulation of continuous-time ΔΣ modulators that is based on behavioral models and which exhibits the best trade-off between accuracy, speed and extensibility compared to other possible techniques that are reviewed briefly in this work. A user-friendly tool, implementing this methodology, is then presented. Nonidealities such as finite gain, finite GBW, output impedance and also nonlinearities such as clipping, harmonic distortion and the important effect of jitter are modeled. Finally, experiments were carried out using the tool, exploring important design trade-offs.