Specifications

4-6. Calibration and compensation in RF region
4-6-1. Calibration
Whether the RF I-V method or network analysis, the open, short and load calibration minimizes
instrument inaccuracies. To perform calibration, open, short and load reference terminations are
connected to the test port and, each of the terminations is measured. This calibration data is stored
in instrument memory and used for calculation to remove the instrument errors. Impedance values
of these reference terminations are indicated in both vector impedance coordinates and smith chart
in Figure 4-13.
Note: A 7 mm coaxial connector has a fringe capacitance of typically 0.082 pF when terminated with open. This fringe
capacitance value has been memorized in the instrument and is used to calculate accurate open calibration data.
Figure 4-13. Calibration standard values
Though all three terminations are indispensable for calibration, the load termination impedance (50
Ω) is particularly important for precise calibration and has a large influence on resultant measure-
ment accuracy. The uncertainty of the load termination impedance is represented by a circle that
encloses the error vector. See Figure 4-13 (a) for a demonstration. The uncertainty of its phase
angle increases with frequency and becomes a considerable error factor, especially, in measure-
ments of high Q (low ESR or low D) devices at high frequencies.
To improve accuracy for the high Q (low loss) measurement, the RF I-V measurement instrument
can be calibrated using a low loss capacitor (LLC) termination in addition to the open/short/load
terminations. The LLC provides a reference for calibration with respect to 90°-phase component of
impedance. As a result, the instrument can measure high Q (low dissipation factor) devices more
accurately than in case of basic open/short/load calibration. The LLC calibration takes place only in
high frequency range (typically above 300 MHz) because the phase angle of the load impedance is
accurate at relatively low frequencies.
4-13
Note: Open impedance is infinit,
so it is not shown in the graph.
(a) Vector impedance plane (b) Smith chart