Femtoampere microcurrent detection system based on logarithmic method

The detection of weak current signals is critical in various fields, yet achieving precise detection of microlevel signals remains a significant challenge. This paper designs a microcurrent meter to detect femtoampere microcurrents. This design constructs a logarithmic amplification circuit with the ADA4530-1 operational amplifier, which features ultra-low bias current and ultra-low noise. To suppress leakage currents, guard rings and PCB hollowing-out are utilized. Additionally, electromagnetic shielding and low-ripple LDO power supply are implemented to minimize noise. A 24-bit high-precision AD conversion module is employed to further enhance accuracy. In experiments, currents above 100 fA are generated using voltage/resistance method, while currents below 100 fA are produced by capturing low-concentration charged nanoparticles using a Faraday cup. The results demonstrate that the microcurrent meter achieves the accuracy of over 86% for currents below 100 fA and over 88% for currents below 10 fA, showing its excellent performance in detecting femtoampere-level microcurrents.