Specifications

5-9
inductor frequency response in Ls – Rs measurement mode is shown in Figure 5-12 (b). The mea-
sured inductance (Lm) rapidly increases as the frequency approaches the SRF because of the effect
of resonance. The maximum Lm value becomes greater as the device has a higher Q factor. At
frequencies above the SRF, a negative inductance value is displayed because the Lm value is calcu-
lated from a capacitive reactance vector, which is opposite to inductive vector.
Figure 5-10. Inductor equivalent circuit
Figure 5-11. Effects of parasitics in actual inductor measurement
Figure 5-12. Typical inductor frequency response
Cp
Ls
Rs
|Z|
Impedance/
phase angle
(q)
0º
–90º
90º
SRF
Frequency
Log f
Log |Z|
q
(a) |Z| -
q
frequency response
Inductance
SRF
Frequency
0
+L
–L
Inductive
Capacitive
L
m =
1 - w
2
C p Ls
Ls
(Negative L m
value )
Equivalent C = = C p (1 - )
w
2
L m
w
2
C
p Ls
1
–1
Effective range of
Log f
(b) Inductance frequency response
C
L
Rs
L
s
= =
(1 – w
2
LC )
2
+ w
2
C
2
R
s
2
L (1 – w
2
LC
–
)
CR
s
2
L
w
X
Ls - R s mode
L
1 – w
2
LC
When w
2
C
2
R
s
2
<< 1 and << 1, Ls
`
L
CR
s
2
C
L
Rs
Z = + j
(1 -
2
LC)
2
+
2
C
2
R
s
2
(1 -
2
LC)
2
+
2
C
2
R
s
2
R
s
L (1
–
2
LC
–
)
CR
s
2
L
Real part (R)
Imaginary part (X)