TABLE OF CONTENTS In Section 8.1 we examined simple C-R-L models and concluded that those models can capture the first-order behavior of the capacitors: the capacitive region, series resonance, and the inductive region. In Sections 8.3 and 8.4 we saw that capacitance, resistance, and inductance are functions of frequency and that they depend on internal and external geometry, as well as on environmental factors. For frequency-domain characterization, the primary concern is the frequency dependency of the C-R-L elements in the equivalent circuit, due to material characteristics and internal/external geometry. Environmental effects usually vary slowly, so they can be taken into account by statically adjusting the parameters in the model.
Multicomponent models are built of frequency-independent C-R-L elements, so they are compatible with both frequency-domain and time-domain simulators.
In bulk capacitors, the important frequency-dependent parameters are capacitance and resistance. Though inductance is also frequency dependent, it is usually a weak function of frequency and a model with a constant inductance is suitable for many applications.
In bulk capacitors, the capacitance (and also the real part of impedance) may be strongly frequency dependent. This is due to the combined effect of large capacitance, (optionally) low ESR, and internal geometry. Simple spreadsheet approximations reveal that a three-element C-R-L equivalent circuit with frequency-independent values may have a noticeable error of impedance prediction close to the series resonance frequency. As an example, we apply a six-element model to the capacitor from Figure 5.20.
