An Improved Sampling-Based Impedance Bridge

This paper describes an improved version of a sampling-based bridge designed for impedance calibration. Based on the original concept of the new multiplexer, which constitutes a key element of the improved impedance bridge, we propose a new procedure for determining the complex voltage ratio using both successive and simultaneous sampling. The procedure significantly improves the accuracy of impedance comparisons by eliminating digitizer gain errors and reducing errors caused by instabilities in the excitation voltages supplied by the precision sources driving the bridge arms. An implementation of the new procedure, employing an innovative cross-multiplexer together with modified software, is presented. We also provide an analysis of selected error sources, including the effects of digitizer nonlinearity, which is crucial when applying the modified method for determining the impedance ratio. Finally, validation results are presented, demonstrating the performance and accuracy of the SUT sampling-based bridge in comparison with another validated bridge used at the Italian National Metrology Institute (INRIM) in Turin.