Electromagnetics Explained

7 THE HIDDEN SCHEMATIC

Typically, schematic diagrams show resistors, capacitors, inductors, and wires as ideal components. In many cases, components can be considered as ideal. However, at high frequencies such approximations are often no longer valid. The frequency-dependent departures from ideality are mainly due to parasitic capacitances and parasitic inductances. Electromagnetic theory dictates that any two conductors will have a capacitance between them and that any conductor used for carrying current will have inductance. Parasitic capacitance and inductance create reactive impedance that varies with frequency. For a capacitor, the impedance is Z_c = –j/2πfC. At DC, capacitive impedance is infinite—an open circuit. Capacitive impedance ...