Performance Study of a Digitally Assisted Impedance Bridge on the Basis of Capacitance Measurements in the Audio Frequency Range

A digitally assisted (DA) coaxial bridge, mainly consisting of a ratio transformer and digital voltage sources, was set up in a four-terminal-pair (4-TP) configuration for precision impedance ratio measurements. A 10:1 capacitance ratio was then measured in the range of 1 pF– $1~ {\mu }\text{F}$ mainly at 1 kHz using the 4-TP DA bridge, and the results were compared to those from the existing two-terminal-pair (2-TP) and three-terminal (3-T) capacitance bridges. The deviations between the capacitance ratio measurements obtained by the different bridges lie from a few parts between 108 and 105, depending on the measurement capabilities of the 2-TP/3-T bridges. Moreover, the measurement frequency of the 4-TP bridge was varied from 50 Hz to 20 kHz, and the frequency dependence of the 10:1 capacitance ratio was studied and compared with the reference ratios. The verification results showed that the existing 2-TP/3-T bridges can be replaced by the new 4-TP DA bridge with an extended measurement range and better uncertainty for capacitance measurements.