An Offset and 1/f-Noise Compensated Current-to-Digital Conversion for Active Pixels in MEA Applications

This work presents a current measurement circuit suitable for microelectrode arrays in active pixel architecture. In chemical applications the exact knowledge of the output or input current is necessary locally in the solution for analysis purposes. Since only a low current is expected due to the microelectrodes, a sensitive and robust measuring circuit must be used. This work presents a concept that makes low currents locally measurable by determining the charging time at a defined capacitance. Process, voltage, temperature variations (PVT), mismatch, and noise typically influence the conversion accuracy of integrated structures. Therefore, the presented concept here combines chopper techniques with some special numerical methods capable of deterministically eliminating the effects of 1/f-noise and local transistor mismatch. Furthermore, the presented structures are modularized in such a way that parts are within an active array pixel and parts are outside the pixel arrangement as a common circuit part of a row or column. For this work the data of a 350 nm CMOS technology was base and the functionality was verified by nominal and statistical simulations.