TABLE OF CONTENTS Many common circuits make use of inductors and capacitors in different ways to achieve their functionality. Filters, impedance matching circuits, resonators, and chokes are common examples. We study these circuits in detail and in particular we shall focus on the desirable properties of the passive components in such circuits.
We begin with the textbook discussion of resonance of RLC circuits. These circuits are simple enough to allow full analysis, and yet rich enough to form the basis for most of the circuits we will study in this chapter.
Incidentally, simple second-order resonant circuits can also model a wide array of physical phenomena, such as pendulums, mass-spring mechanical resonators, molecular resonance, microwave cavities, sections of transmission lines, and even large-scale structures such as bridges. Understanding these circuits will afford a wide perspective into many physical situations.
The RLC circuit shown in Fig. 7.1 is deceptively simple. The impedance seen by the source is simply given by
The impedance is purely real at the resonant frequency when 
( Z) = 0, or 
. At resonance the impedance takes on a minimal value. It is worthwhile to investigate the cause of resonance, or the cancellation of the reactive components due to the inductor and capacitor. Since the inductor and capacitor voltages are always 180 out of phase, and one reactance is dropping while the other is increasing, there is clearly always a frequency when the magnitudes are...
