A 25kHz-BW 97.4dB-SNDR 100.2dB-DR 3rd-Order SAR-Assisted CT DSM with 1–0 MASH and DNC

Continuous-time delta-sigma modulators (CT DSMs) have been a popular choice for high-resolution applications such as audio devices and sensors due to their inherent anti-aliasing, easy driving capability, and relaxed amplifier requirements [1]–[2]. In typical DSMs, the noise-shaping order is directly proportional to the number of integrators used. As an alternative, a single-loop DSM with a digital noise coupling (DNC) topology [3] can be used to provide aggressive noise-shaping without increasing the order of the loop filter (LF) by moving the analog burden to the digital side. In [3]–[5], a DNC structure utilizes a single successive-approximation-register (SAR) quantizer and a robust NC filter composed of simple digital cells (Fig. 1a). Inevitably, however, the DNC architecture displays a low maximum stable amplitude (MSA) owing to the high out-of-band gain (OBG) and the large quantization error of the main ADC. The latter issue can be alleviated using a MASH architecture in which the quantization error of the first stage is eliminated by a digital filter, resulting in a high MSA and more reliable stability.