A 4th-order CT I-DSM with Digital Noise Coupling and Input Pre-conversion Method for Initialization

Abstract

Recently, continuous-time incremental delta-sigma modulators (CT I-DSM) are increasing in popularity for use in sensor readout applications [1,2] due to their high-resolution and input multiplexing ability. For a modulator to be used with a moderate or low oversampling ratio (OSR) considering the input multiplexing, high-order noise-shaping is required to achieve low noise. A multistage noise-shaping (MASH) topology could be one of the candidates to increase the order of noise-shaping without compromising stability. However, as the mismatch between analog and digital filters causes noise leakage in MASH architectures, CT operation would make it more problematic with the process variations. In contrast, a digital noise coupling (DNC) technique [3] not only increases the order of noise-shaping without affecting stability but also is robust to process-voltage-temperature (PVT) variation as a digital filter is utilized for noise-shaping.