20.5 A Sub-pA ΔΣ Current Amplifier for Single-Molecule Nanosensors

Current readout has been a known technique since the inception of electronic sensors and is widely used, for example, in radiation detectors, impedance spectroscopy, and mechanical sensors. Recently, new challenges have emerged for current sensing in the upcoming era of nanosensors. Nanowires, carbon nanotubes and nanopores are emerging devices that have been proven to be effective in sensing ultra-low concentrations of target molecules [1]. For those devices, current sensing becomes challenging since outputs consist of signals in the pA range or less, in the kHz band. To measure these values, very low-noise front-end amplifiers are needed such as the one in [2]. It achieves a noise floor as low as 20fA
rms
at 1kHz and it is designed for electrophysiology experiments, such as in patch clamp techniques, where single-ion channel recordings from cell membranes are required. However, the instrument is bulky and needs a cooled headstage to boost performance. An integrated solution offering quad current-input 20b analog-to-digital converters is reported in [3]. However, its measured equivalent input noise is above 700fA
rms
at 1kHz.