Specifications
When both series and parallel resistances have a considerable amount of influence on the imped-
ance of a reactive device, neither the series nor parallel equivalent circuit models may serve to accu-
rately represent the real C, L, or R value of the device. In the case of the capacitive device shown in
Figure 1-19, both series and parallel mode capacitance (Cs and Cp) measurement values at 1 MHz
are different from the real capacitance of the device. The correct capacitance value can be deter-
mined by deriving three-element (C-Rp-Rs) equivalent circuit parameters from the measured imped-
ance characteristic. In practice, C-V characteristics measurement for an ultra-thin CMOS gate capac-
itance often requires a three-element (C-Rs-Rp) equivalent circuit model to be used for deriving real
capacitance without being affected by Rs and Rp.
Figure 1-19. Example of capacitive device affected by both Rs and Rp
By measuring impedance at a frequency you can acquire a set of the equivalent resistance and reac-
tance values, but it is not enough to determine more than two equivalent circuit elements. In order
to derive the values of more than two equivalent circuit elements for a sophisticated model, a com-
ponent needs to be measured at least at two frequencies. Agilent impedance analyzers have the
equivalent circuit analysis function that automatically calculates the equivalent circuit elements for
three- or four-element models from a result of a swept frequency measurement. The details of selec-
table three-/four-element equivalent circuit models and the equivalent circuit analysis function are
described in Section 5.15.
Frequency (Hz)
Capacitance (pF)
10.0
10.1
10.2
10.3
10.4
10.5
9.9
9.8
9.7
9.6
9.5
100 k 1 M 10 M
Dissipation factor (D)
0.1
0.0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Cp
Cs
D
Frequency (Hz)
Capacitance (pF)
10.0
10.1
10.2
10.3
10.4
10.5
9.9
9.8
9.7
9.6
9.5
100 k 1 M 10 M
Dissipation factor (D)
0.1
0.0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Cp
Cs
D
C
Rs
Rp
70
0
150
k
Xc = 15.9
k at 1 MHz
10 pF
Cs = C +
2
CRp
2
1
Cp =
CRp
2
(Rs + Rp)
2
+
2
C
2
Rp
2
Rs
2
D = CRs + )
CRp
1Rs
Rp
Cp = 9.89 pF
Cs = 10.11 pF
(1 +
1-14