Specifications

1.2 Measuring impedance
To find the impedance, we need to measure at least two values because impedance is a complex
quantity. Many modern impedance measuring instruments measure the real and the imaginary parts
of an impedance vector and then convert them into the desired parameters such as |Z|, θ, |Y|, R, X,
G, B, C, and L. It is only necessary to connect the unknown component, circuit, or material to the
instrument. Measurement ranges and accuracy for a variety of impedance parameters are deter-
mined from those specified for impedance measurement.
Automated measurement instruments allow you to make a measurement by merely connecting the
unknown component, circuit, or material to the instrument. However, sometimes the instrument
will display an unexpected result (too high or too low.) One possible cause of this problem is incor-
rect measurement technique, or the natural behavior of the unknown device. In this section, we will
focus on the traditional passive components and discuss their natural behavior in the real world as
compared to their ideal behavior.
1.3 Parasitics: There are no pure R, C, and L components
The principal attributes of L, C, and R components are generally represented by the nominal values
of capacitance, inductance, or resistance at specified or standardized conditions. However, all cir-
cuit components are neither purely resistive, nor purely reactive. They involve both of these imped-
ance elements. This means that all real-world devices have parasitics—unwanted inductance in resis-
tors, unwanted resistance in capacitors, unwanted capacitance in inductors, etc. Different materials
and manufacturing technologies produce varying amounts of parasitics. In fact, many
parasitics reside in components, affecting both a component’s usefulness and the accuracy with
which you can determine its resistance, capacitance, or inductance. With the combination of the
component’s primary element and parasitics, a component will be like a complex circuit, if it is
represented by an equivalent circuit model as shown in Figure 1-5.
Figure 1-5. Component (capacitor) with parasitics represented by an electrical equivalent circuit
Since the parasitics affect the characteristics of components, the C, L, R, D, Q, and other inherent
impedance parameter values vary depending on the operating conditions of the components.
Typical dependence on the operating conditions is described in Section 1.5.
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