Performance Study of a Digital Impedance Bridge on the basis of Capacitance Measurements in Audio Frequency

A digitally assisted coaxial bridge-mainly consisted of a ratio transformer and digital voltage sources-was set up in a 4-terminal-pair (4-TP) configuration for the precision capacitance measurements. The 10: 1 capacitance ratio was measured in the range of 1 pF ~ 1 μF mainly at 1 kHz using the 4-TP bridge. The measurement results show a degree of equivalence from a few parts in 10 ⁸ to 10 ⁵ when compared with those obtained using 2-terminal-pair/3-terminal bridges. Moreover, the measurement frequency of the 4-TP bridge was varied from 50 Hz to 20 kHz. The Allan deviation measurements imply that the statistical uncertainty could be achieved a level of 10 ^-9 at 1 kHz.