In this tutorial we are going to learn about WHAT IS THE FREQUENCY CHARACTERISTICS OF PASSIVE COMPONENTS ?
Many designers are ignorant of the frequency limitations of the passive components they use in analog circuit. In Passive components have limited frequency ranges, and operation of the part outside of that range can have some unexpected results. In most cases, a Good passive component will fit on the same pads as a Not good passive component, but not always. Start the design process by carefully considering the High Frequency characteristics of passive components & putting the correct part outline on the board from the start.
High Frequency performance of resistance is approximated by the schematic shown in figure:
Resistors are constructed 3 ways, wire wound, carbon composition, & film. It is understand how wire wound resistors can become inductive, because they are coils of Restive wire. Film resistors are also coils of thin metallic film. Therefore, they are also inductive at High Frequencies. The end caps of resistors are parallel, & there will be an associated capacitance. Generally, the resistance will create the parasitic capacitor so “leaky” that the capacitance does not matter. For very high resistances, the capacitance will appear in parallel with the resistance, lowering its impedance at HF’s.
High Frequency performance of capacitors is approximated by the figure
Film & electrolytic capacitors have layers of material wound around each other, which make a parasitic inductance. ceramic capacitors of self inductance effects much smaller, giving them a higher operating frequency. There is also some leakage current from plate to plate R , which appears as a resistance in parallel with the capacitor. The most important parasitic component in a capacitor is the ESR. It is due to resistance within the plates & electrolyte of an electrolytic capacitor. Decoupling capacitor should be low ESR types, as any series resistance limits the effectiveness of the capacitor for ripple & noise rejection. Elevated temperatures severely increases ESR, & can be permanently destructive to capacitors. The leads of Through Hole capacitor also add a parasitic inductance. For small values of capacitance, it is important to keep the lead lengths short. The combination of parasitic inductance & capacitance can produce resonant circuits.