A Digital Bridge Evaluation up to 100 kHz for Precision Impedance Measurements

A digital coaxial bridge was evaluated for its frequency extension up to 100 kHz using impedance standards with known reference values. The bridge can be configured in different modes of what are known as digitally assisted (DA) or fully digital (FD) modes, and both were studied. The measurement results showed that the FD bridge cannot reach an accuracy below $100\times 10^{-6}$ at 100 kHz, even for 1:1 comparison, unlike the DA bridge. Thus, an additional voltage injection method was attempted to achieve better accuracy for the FD bridge. As a result, 10:1 capacitance ratio measurements showed a good agreement with the reference values at the level of $10^{-5}$ for both DA and FD bridges at the highest frequency of 100 kHz.