A 105.7 dB SNDR 176.1 dB FoMs dynamic zoom ADC with noise-coupled enhancement

In zoom analog-to-digital converters (ADCs), due to the dynamic updating and scaling of fine reference voltages by coarse SAR ADC, traditional noise coupling technique cannot be directly applied to fine ΔΣ modulator, which may lead to modulator overload and a sharp decline in the signal-to-noise distortion ratio (SNDR). To address this issue, this article proposes a noise-coupled technique specifically designed for zoom ADCs. It establishes a mathematical model and determines the appropriate feedback voltage based on coarse quantization and the over-ranging factor, ultimately enhancing SNDR and energy efficiency. The zoom ADC is designed using a 180 nm CMOS process and incorporates two integrators to achieve 3rd-order noise-shaping capability (60 dB/dec). It achieves an SNDR of 105.7 dB at a sampling frequency of 256 kHz and an oversampling rate of 128, with a power consumption of only 90.25 μW. The SNDR-based Schreier figure-of-merit (FoMs) is 176.1 dB, indicating competitive performance in terms of high resolution and energy efficiency.