APPLICATION NOTE
3
A small resistor does not exhibit much shunt capacitance, but its impedance increases with frequency
due to the series inductance. In case of large resistors, the capacitance reduces the impedance as
frequency increases, whereas the inductance is negligible.
Figure 2: Impedance versus Frequency
Figure 2 shows a plot of impedance versus frequency for several resistor values. This plot clearly
illustrates that a resistance value has a huge effect on resistor's behavior at higher frequencies.
Ceramic Capacitor Models
Multilayer ceramic capacitors have much the same parasitic elements as a resistor, but are slightly
rearranged. Figure 3 illustrates the behavior of a frequency-dependent model for a basic leaded ceramic
capacitor, plotting impedance versus frequency for several typical part values. The equivalent series
resistance (ESR) limits the Q of the capacitor; the parasitic inductance and capacitance value set the self-
resonant frequency.
Figure 3: Ceramic Capacitor Model Behavior
All capacitors self-resonate at some frequency, after which the impedance starts to climb inductively.
