- 6 -
There are two factors to provide the ratio of real part and
imaginary part. Usually the quality factor
Q
is used for
inductance measurement and the dissipation factor
D
is used
for capacitance measurement.
D
factor is defined as a
reciprocal of
Q
factor.
Q = 1 / D = tan
ș
Q = Xs / Rs = 2
ʌ
f Ls / Rs = 1 / 2
ʌ
f Cs Rs
Q = B / G = Rp / | Xp | = Rp / 2
ʌ
f Lp = 2
ʌ
f Cp Rp
Actually, Rs and Rp are existed in the equivalent circuit of
capacitor or inductor. If the capacitor is small, Rp is more
important than Rs. If capacitor is large, the Rs is more
important also. Therefore, use parallel mode to measure lower
value capacitor and use series mode to measure higher value
capacitor. For inductor, the impedance relationship is different
from capacitor. If the inductor is small, Rp is almost no effect. If
inductor is large, the Rs is no effect also. Therefore, use series
mode to measure lower value inductor and use parallel mode to
measure higher value inductor.
Open/short calibration
process to get the better accuracy for high/low impedance
measurement. The purpose of open/short calibration is to
reduce the parasitic effect of the test fixture.
- 7 -
Z
M
is defined as total impedance measured to DUT
( device under test ) by the special test fixture which has some
parasitic impedance.
Z
M
= (Rs + j
Ȧ
Ls) + ((Go+j
Ȧ
Co)-1 || Z
DUT
)
Z
DUT
is the target impedance user wants to realize. It is
necessary to use the open/short calibration process to cancel
the effect of
Rs+j
Ȧ
Ls
and
Go+j
Ȧ
Co
.
Equivalent circuit