A 115.6 dB SNDR MASH 2-2 Sigma–Delta ADC with Double-Sampling Integrator and Nonuniform Quantizer for Wearable Biomedical Devices

To meet the demand for high-precision biological signal detection in wearable biomedical devices, this paper proposes the design of a fourth-order discrete-time sigma–delta analog-to-digital converter (ADC) employing a multi-stage noise shaping (MASH) 2-2 architecture. In the first-stage sub-modulator, the first integrator adopts a double-sampling structure, which improves noise shaping performance markedly. A novel common-mode feedback (CMFB) circuit has also been designed, which addresses the phase-dependent loading issue in traditional switched-capacitor networks. Notably, a dynamically activated nonuniform quantization mode is innovatively proposed in the second stage. It integrates 2.5-bit coarse quantization with 2-bit fine quantization in specific intervals, enabling high-precision detection of the small-amplitude quantization errors from the first-stage sub-modulator. In addition, the comparator in this stage integrates feed-forward summation capability and retains input offset voltage storage (IOS) technology to reduce the offset voltage. Meanwhile, the designs of dynamically activated nonuniform quantizer and comparator with integrated summation function have reduced the power consumption of the modulator by 19%. In a 180-nm CMOS process, the modulator occupies a layout area of 0.57[Formula: see text]mm 2 and simulation results indicate a peak signal-to-noise-and-distortion ratio (SNDR) of 113.2[Formula: see text]dB. After processing by the cascaded integrator comb (CIC) decimation filter, the ADC achieves a peak SNDR of 115.6[Formula: see text]dB, an effective number of bits (ENOB) of 18.91 bits and a power consumption of 4.36[Formula: see text]mW under a 1.8[Formula: see text]V supply. These performance metrics correspond to a state-of-the-art figure-of-merit (FoM) of 175.1[Formula: see text]dB.