Performance Evaluation of Incremental Sigma-Delta ADCs Based on their NTF
Johannes Wagner, Patrick Vogelmann, Maurits Ortmanns
Abstract
In this brief the performance of I-SD ADCs based on the spectral description is discussed. It is based on the modulator and the reconstruction filter and accounts for the applied reset. The definition of the overall noise transfer function (NTF) enables the analysis of the performance of I-SD ADCs in frequency domain and consequently makes it possible to explain the inherent behavior of this type of ADC including reconstruction filter and non-idealities. In the state of the art, the performance of an I-SD ADC is either obtained by simulations or predicted via time-domain considerations. However, these simulations can become time consuming and time-domain considerations neglect non-idealities, especially in the case of a CT modulator. Only recently, a general way to describe the NTF of DT and CT I-SD ADCs was introduced. This brief gives a detailed analysis of the NTF of I-SD ADCs and the impact of its properties on the resulting SQNR. It discusses the influence of common reconstruction filters and based on this analysis, it introduces as an example a modified CoI filter that allows to improve the ADC's performance.