Difference amplifiers are a very compact solution to measure µA currents. For a solution that can measure down to nA currents, see our "Highest Accuracy after calibration" and "Highest Accuracy" signal chains. A high voltage buffer is added in-front of the DiffAmp to minimize the bias current error as well as to maintain the resistor matching of the DiffAmp to avoid any degradation in CMRR performance.
