A noise model for full characterization of discrete-time current sensing

Current sensing is a widely used technique for reading out sensors. However, its application becomes challenging in presence of very low level of signals such as those generated by nanosensors. Thus, the characterization of noise plays a fundamental role for determining the limits of detection of the electronic interface. Two general approaches are followed for achieving low-noise current sensing based on discrete-time (DT) and continuous-time (CT) architectures, showing quite different trade-off rules to set resolution and bandwidth. Most papers treat noise in current sensing interfaces referring to a continuous-time model. Unfortunately, this model cannot be applied to DT approaches where folding effects on noise may be dominant over other contributions. To our knowledge, no paper has so far fully characterized a current sensing interface in DT domains. This paper derives a noise model of a DT current interface that uses correlated double sensing (CDS) technique showing very good agreements with simulation and testing results. The model would allow simplifying the design constraints to optimize the overall circuit performance.