Specifications

5-12
Figure 5-16 shows the measured vector of a high Q inductor. Except for the resonant method, the
impedance measurement instrument calculates the Q value by Q = X/R. The impedance measure-
ment error is represented by a small circle enclosing the error vector (D). The R value of a high Q
(low loss) inductor is very small relative to the X value. Small changes in R results in large Q value
changes (Q = X/R). Therefore, error in the R measurement can cause significant error in the Q fac-
tor, especially in high Q devices. A negative Q problem also arises from the Q (D) measurement error
as described in Section 5.1.3.
Figure 5-16. Q measurement error
The following methods deliver improvement to Q measurement accuracy:
(1) Use the instrument with better accuracy
(2) Perform optimum compensation for residual resistance and cable length
(3) Use an equivalent circuit analysis function and calculate the Q value from the equivalent circuit
parameter values obtained for the DUT (refer to Section 5.15.)