Design and implementation of a transresistance amplifier for accurate current measurements in the microampere range

This article presents the design, implementation and preliminary verification of a transresistance amplifier suitable for the operation with calibrated external resistance standards, allowing traceable and accurate current measurements in the microampere range. Traditionally, the traceability of current measurements is ensured by calibration through the injection into a transresistance amplifier of one or more calibrated currents. The transresistance amplifier presented in this work allows for an alternative traceability path, in which the calibration is ensured by an external calibrated resistance standard and the accuracy of the transresistance gain. The transresistance amplifier has been designed for an accuracy of the transresistance gain at the level of 0.1 μΩ/Ω with respect to the external transresistance value. The transresistance gain error has been experimentally verified with an uncertainty at the level of 0.3 μΩ/Ω (coverage factor of 2). The current measurement uncertainty introduced by this transresistance amplifier is thus at the 0.1 μA/A level.