A High-Sensitivity Large-Dynamic-Range Current-Domain Continuous-Time Zoom ADC for Current-Sensing Front-End

TLDR: In this paper , an fA-level-sensitivity and 115-dB-DR current domain (CD) continuous-time (CT) Zoom ADC-based CSFE is presented, which achieves the power efficiency of 389 nJ per conversion and a resolution Figure-of-Merit (FoM) of 0.13 pA.

Abstract: Ultrahigh sensitivity and large-dynamic-range (DR) current-sensing front-ends (CSFEs) are required in emerging biomedical applications like next-generation gene-sequencers (NGGSs). In this article, an fA-level-sensitivity and 115-dB-DR current-domain (CD) continuous-time (CT) Zoom ADC-based CSFE is presented. Three main techniques are proposed, including: 1) a novel resistive-DAC (RDAC) with ultralow noise and a compact area to achieve an fA-level sensitivity; 2) a CD CT SAR ADC serves as a coarse quantizer to extend the DR to be over 115 dB; and 3) a digital compensation scheme overcomes the offset problem of the big parasitic capacitor at the input node. Fabricated in a 180-nm CMOS process, this chip only occupies an active area of 0.182 mm2 and consumes <inline-formula> <tex-math notation="LaTeX">$77 \mu \text{W}$ </tex-math></inline-formula> at a 2-V supply voltage. At a 100-Hz bandwidth (BW), it achieves the power efficiency of 389 nJ per conversion and a resolution Figure-of-Merit (FoM<inline-formula> <tex-math notation="LaTeX">$_{\text {res}}$ </tex-math></inline-formula>) of 0.13 pA<inline-formula> <tex-math notation="LaTeX">$^{{2}}\mu \text{J}$ </tex-math></inline-formula>.