Correlated Dual-Loop Sturdy MASH Continuous-Time Delta-Sigma Modulators

This article presents a new multi-loop delta-sigma modulator (DSM) structure that combines the advantages of both the traditional multi-stage noise shaping (MASH) and sturdy MASH (SMASH) architectures. It removes the need for an explicit quantization error extraction digital-to-analog converter (DAC) typically required in multi-loop structures, which allows to eliminate the delay mismatch problem related to the intrinsic propagation delay of the first loop quantizer. The proposed architecture essentially uses the SMASH architecture as its core and has similar characteristics. However, it further simplifies the structure allowing to remove all the feedback DACs in the cascaded loop. The prototype DSM fabricated in a 65-nm process achieves signal-to-noise-and-distortion ratio (SNDR) and dynamic range (DR) of 73.4 and 78.3 dB, respectively, in an 18.75-MHz bandwidth. With 1.1/1.5-V (1.5 V for DAC) supply voltage, the prototype DSM consumes 17.85 mW at 600-MHz operating speed corresponding to a Walden and Schreier figure of merits (FOMs) of 124.1 fJ/conv-step and 168.6 dB (using DR result), respectively.