Specifications

1.0 Impedance Measurement Basics
1.1 Impedance
Impedance is an important parameter used to characterize electronic circuits, components, and the
materials used to make components. Impedance (Z) is generally defined as the total opposition a
device or circuit offers to the flow of an alternating current (AC) at a given frequency, and is repre-
sented as a complex quantity which is graphically shown on a vector plane. An impedance vector
consists of a real part (resistance, R) and an imaginary part (reactance, X) as shown in Figure 1-1.
Impedance can be expressed using the rectangular-coordinate form R + jX or in the polar form as a
magnitude and phase angle: |Z|_ θ. Figure 1-1 also shows the mathematical relationship between R,
X, |Z|, and θ. In some cases, using the reciprocal of impedance is mathematically expedient. In
which case 1/Z = 1/(R + jX) = Y = G + jB, where Y represents admittance, G conductance, and B sus-
ceptance. The unit of impedance is the ohm (Ω), and admittance is the siemen (S). Impedance is a
commonly used parameter and is especially useful for representing a series connection of resistance
and reactance, because it can be expressed simply as a sum, R and X. For a parallel connection, it is
better to use admittance (see Figure 1-2.)
Figure 1-1. Impedance (Z) consists of a real part (R) and an imaginary part (X)
Figure 1-2. Expression of series and parallel combination of real and imaginary components
1-1