10.2 A 139 µ W 104.8dB-DR 24 kHz-BW CT ΔΣM with Chopped AC-Coupled OTA-Stacking and FIR DACs

Abstract

Continuous-time delta-sigma modulators (CT $\Delta \Sigma \mathrm{Ms}$) have inherent anti-aliasing, resistive inputs, and relaxed settling requirements making them popular for audio applications. Due to the relatively low bandwidth, the noise-efficiency of the first OTA has a substantial influence on the power and FoM. OTA-stacking is a recently reported technique that improves the noise-current tradeoff in continuous-time amplifiers [1], [2]. This is the central idea behind the proposed CT $\Delta\Sigma$ M where an AC-coupled stacked OTA improves the noise-efficiency of the first integrator. The ADC with a 3-stack OTA achieves 100.9 dB SNDR and $104.8 \mathrm{dB} \mathrm{DR}$ in a 24 kHz bandwidth while consuming $139 \mu \mathrm{W}$ for a state-of-the-art Schreier $FoM _{\mathrm{DR}}$ of 187.2 dB.