Specifications

1.7 Measurement circuit modes
As we learned in Section 1.2, measurement instruments basically measure the real and imaginary
parts of impedance and calculate from them a variety of impedance parameters such as R, X, G, B,
C, and L. You can choose from series and parallel measurement circuit modes to obtain the mea-
sured parameter values for the desired equivalent circuit model (series or parallel) of a component
as shown in Table 1-1.
Table 1-1. Measurement circuit modes
Equivalent circuit models of component Measurement circuit modes and impedance parameters
Series Series mode: Cs, Ls, Rs, Xs
Parallel Parallel mode: Cp, Lp, Rp, Gp, Bp
Though impedance parameters of a component can be expressed by whichever circuit mode (series
or parallel) is used, either mode is suited to characterize the component at your desired frequencies.
Selecting an appropriate measurement circuit mode is often vital for accurate analysis of the rela-
tionships between parasitics and the component’s physical composition or material properties. One
of the reasons is that the calculated values of C, L, R, and other parameters are different depending
on the measurement circuit mode as described later. Of course, defining the series or parallel equiv-
alent circuit model of a component is fundamental to determining which measurement circuit mode
(series or parallel) should be used when measuring C, L, R, and other impedance parameters
of components. The criteria shown in Figure 1-15 can also be used as a guideline for selecting the
measurement circuit mode suitable for a component.
Table 1-2 shows the definitions of impedance measurement parameters for the series and parallel
modes. For the parallel mode, admittance parameters are used to facilitate parameter calculations.
Table 1-2. Definitions of impedance parameters for series and parallel modes
Series mode Parallel mode
|Z| = √Rs
2
+ Xs
2
|Y| = √Gp
2
+ Bp
2
q = tan
–1
(Xs/Rs) q = tan
–1
(Bp/Gp)
Rs: Series resistance Gp: Parallel conductance (= 1/Rp)
Xs: Series reactance (X
L
= wLs, X
C
= –1/(wCs)) Bp: Parallel susceptance (B
C
= wCp, B
L
= –1/(wLp))
Ls: Series inductance (= X
L
/w) Lp: Parallel inductance (= –1/(wB
L
))
Cs: Series capacitance (= –1/(wX
C
)) Cp: Parallel capacitance (= B
C
/w)
D: Dissipation factor (= Rs/Xs = Rs/(wLs) or wCsRs) D: Dissipation factor (= Gp/Bp = Gp/(wCp)
Q: Quality factor (= Xs/Rs = wLs/Rs or 1/(wCsRs)) = 1/(wCpRp) or wLpGp = wLp/Rp)
Q: Quality factor (= Bp/Gp = wCp/Gp
= wCpRp or 1/(wLpGp) = Rp/(wLp))
Gp
±jBp
Rs
±jXs
G
jB
RjX
1-10