A 99.8-dB SNDR 10kHz-BW Second-Order DT Delta-Sigma Modulator with Single OTA and Enhanced Noise-Coupling

This paper presents a low-power second-order discrete-time (DT) Delta-Sigma Modulator (DSM) for Internet of Things (IoT) applications. The conventional noise coupling (NC) topology is improved with additional dual feedback paths to suppress the high-frequency gain of the noise transfer function (NTF), thereby reducing the internal voltage swing and relaxing the requirement of the quantizer resolution. In addition, stage-sharing technique is applied to reuse the OTA for both the integrator and the NC adder. Hence, second-order noise shaping is achieved with a single OTA. Implemented in a 130nm CMOS process, the proposed design demonstrated a simulated SNDR of 99.8dB in a 10kHz bandwidth with a 5.12MS/s sampling rate, consuming 200μW. State-of-the-art Schreier FoM (SNDR) and Walden FoM of 176.8dB and 125fJ/conv-step are achieved.