Specifications

1-8
1.5.4 Temperature
Most types of components are temperature dependent. The temperature coefficient is an important
specification for resistors, inductors, and capacitors. Figure 1-12 shows some typical temperature
dependencies that affect ceramic capacitors with different dielectrics.
1.5.5 Other dependency factors
Other physical and electrical environments, e.g., humidity, magnetic fields, light, atmosphere, vibra-
tion, and time, may change the impedance value. For example, the capacitance of a high-K type
dielectric ceramic capacitor decreases with age as shown in Figure 1-13.
1.6 Equivalent circuit models of components
Even if an equivalent circuit of a device involving parasitics is complex, it can be lumped as the sim-
plest series or parallel circuit model, which represents the real and imaginary (resistive and reac-
tive) parts of total equivalent circuit impedance. For instance, Figure 1-14 (a) shows a complex
equivalent circuit of a capacitor. In fact, capacitors have small amounts of parasitic elements that
behave as series resistance (Rs), series inductance (Ls), and parallel resistance (Rp or 1/G.) In a suf-
ficiently low frequency region, compared with the SRF, parasitic inductance (Ls) can be ignored.
When the capacitor exhibits a high reactance (1/(wC)), parallel resistance (Rp) is the prime determi-
native, relative to series resistance (Rs), for the real part of the capacitor’s impedance. Accordingly,
a parallel equivalent circuit consisting of C and Rp (or G) is a rational approximation to the complex
circuit model. When the reactance of a capacitor is low, Rs is a more significant determinative than
Rp. Thus, a series equivalent circuit comes to the approximate model. As for a complex equivalent
circuit of an inductor such as that shown in Figure 1-14 (b), stray capacitance (Cp) can be ignored in
the low frequency region. When the inductor has a low reactance, (wL), a series equivalent circuit
model consisting of L and Rs can be deemed as a good approximation. The resistance, Rs, of a series
equivalent circuit is usually called equivalent series resistance (ESR).
Figure 1-12. Temperature dependency of ceramic capacitors Figure 1-13. Aging dependency of ceramic capacitors