Accurate Immittance Measurements at Frequencies up to 20 MHz

Immittance-measuring facilities have been developed that yield high accuracy over a wide immittance range at frequencies up to 20 MHz. The achievement of accuracy at high frequencies required that the errors resulting from residual immittances be kept small, which in turn required development work in bridge design, calibration techniques, measurement methods, and the intercomparison of measurement results. These activities included the design and calibration of unity-ratio admittance bridges, the use of additional circuitry with these bridges to measure small impedances, and the modeling of the impedances of small-valued inductors. Examples of the resulting accuracies for the values assigned to high-Q inductors are at 1 MHz, approximately ± t(0.1 percent+0.5 nH) in inductance and ±(0.01 Q percent+0.3 mQ) in resistance for 50-nH to 100-μH inductors; and at 10 MHz, ±0.5 percent in inductance and ±0.5 Q percent in resistance for 0.5-μH to 3 IH inductors.