A 10kHz-BW 103.1-dB Max-SNDR Reconfigurable Zoom ADC With Noise-Shaping Effect Enhancement Technique for Biomedical Measurement

This article introduces a 10kHz-BW discrete-time (DT) resolution-reconfigurable zoom analog-to-digital converter (ADC) for biomedical applications. By setting the sampling rate $f_{s}$ to 1, 2, 3, or 4 MS/s, corresponding to oversampling ratios (OSRs) of 50, 100, 150, or 200, respectively, the ADC can operate in four distinct modes, supporting resolutions of 12, 14, 16, or 18 bits. A noise-shaping enhancement technique, aiming at optimizing OSR-related poles of the noise transfer function (NTF) for specific modes, is adopted to reinforce the noise-shaping effect when the OSR is altered. The prototype ADC, which integrated a third-order sigma-delta modulator and a 6-bit successive-approximation register (SAR) ADC, was fabricated in a 0.18 $\mu $ m BCD process and occupied a core area of 0.25 mm2. Measurements indicate that a maximum signal-to-noise-and-distortion ratio (SNDR) of 103.1 dB on condition of a sampling rate of 4 MS/s can be achieved. Thanks to the employed noise-shaping enhancement technique, the SNDR can be improved further by 2.2, 4.3, and 6.7 dB corresponding to sampling rates of 1, 2, and 3 MS/s, showcasing the effectiveness of the proposed noise-shaping enhancement technique.