A Mixed-Signal I-D-TIA With Direct Digitization [Technical Note]

Emerging sensing techniques impose strict requirements on the analog frontend regarding noise, bandwidth (BW), scalability, etc. For example, in nanopore-based DNA sequencing, two buffer solutions are separated by a membrane with a nanometer-sized pore. As molecules pass through the pore, they change the ionic current, producing a very small signal (MHz) is required in the sensing circuit [1]. Another example is scanning ion conductance microscopy, where a pipettewith an opening of a fewhundred nanometers is scanned over a small object (e.g., a cell or bacterium). The ionic current (hundres of pA) through the pipette varies with the object’s distance, thus a topographical image can be generated. To achieve high scan rates, a large BW(>100kHz) is required in the analog sensing front-end [2].