IMPEDANCE THEORY
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 represented 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-2.
Figure- 2. Impedance
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-3 also shows the mathematical relationship between R, X, |Z|
and
θ
.
The unit of impedance is the ohm (
Ω
). 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.
4