A femto-ampere sensitive direct-interface current-input sigma delta ADC for amperometric bio-sensor signal acquisition

In this paper we present an ultra-low current measurement platform for amperometric bio-sensor readout. A current mode continuous-time sigma delta ADC is implemented and used as a direct interface to the bio-sensor, thereby omitting any intermediate frontend circuitry. This results in a low noise and low power readout suitable for compact integration. The ADC is reconfigurable and has a programmable dynamic range extending from 25nA to 250μA, along with a scalable clock allowing different conversion times. The wide dynamic range supports a variety of applications ranging from solid-state nanopores (pA), carbon nanotubes (nA) and certain protein based electrochemical bio-sensors (μA). Measurements show an integrated noise current of 314fA in a 100 Hz bandwidth, resulting in a resolution of 19bit. The chip dissipates 1.7mW and achieves a FOM of 162.6 dB.