Wideband Continuous-Time MASH Delta-Sigma Modulators: A Tutorial Review

The maximum sampling frequency of oversampled continuous-time (CT) delta-sigma modulators (DSM) has increased considerably over the past decade. Plus, with its implicit anti-aliasing filtering and resistive input impedance, it results in a substitution of discrete-time pipeline ADCs in wireless receivers. For CT DSMs, multi-stage noise-shaping (MASH) topology features a cascade of low-order loops, thus allowing the exploration of larger sampling rate when compared with a single-loop topology. However, the inherent quantization noise (QN) leakage constrains the achievable resolution of the MASH DSM. Besides, the QN extraction of preceding stages is problematic in CT MASH with very fast sampling rates. This brief review the fundamentals and design considerations of CT MASHs. It highlights recent state-of-the-art CT MASH addressing the above design challenges, including architectural advances, circuitry innovation and digital calibration. This brief intends to serve as a starting point in the forthcoming development of a wideband low-power CT MASH DSM.