A 1.96Vpp Input-Range 3rd-order Noise-Shaping Pipelined-SAR ADC with Self-Boosted Impedance and Active Charge Sharing for Biosignal Acquisition

Wearable healthcare devices require front ends with high input impedance (Ziv), low power and high resolution (uV-level) with area efficiency in the presence of large artifacts and DC offset. The conventional architecture of instrument amplifier (IA)+ADC has low dynamic range (DR), suffering from artifacts which easily cause IAs saturation [1], [2]. In contrast, the direct-conversion ADC front end is promising due to its high DR with lower power. The continuous-time DSM (CTDSM) is advantageous in $\mathrm{Z}_{\mathrm{IN}}$ and area [3], but suffers from 1/f noise and limited input range. CTDSMs with the chopping technique [4]–[6] mitigate 1/f noise at the cost of reduced Zin (Fig. 1 (a)). SAR/Noise shaping (NS)-SAR ADCs [7–9] have intrinsic large input range, hence being tolerable to artifacts and offset (Fig.1(b)). However, due to the large sampling capacitor limited by kT/C noise, $\mathrm{Z}_{\mathrm{IN}}$ and area efficiency of the NS-SAR ADC are low, which hinders its adoption in biosignal acquisition. Moreover, the state-of-the-art (SOTA) direct-conversion ADC require a separate accuracy-limited Zin booster for high Zin and a high over-sampling rate (OSR) for high resolution, which degrades power and hardware efficiency.