14.1 Introduction

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14.1 Introduction

In our sinusoidal circuit analysis, we ha ve learned ho w to find voltages and currents in a circuit with a constant frequency source. If we let the amplitude of the sinusoidal source remain constant and v ary the frequency, we obtain the circuit’ s frequency r esponse. The frequency response may be re garded as a complete description of the sinusoidal steady-state behavior of a circuit as a function of frequency.

The frequency response of a circuit is the variation in its behavior with change in signal frequency.

The sinusoidal steady-state frequenc y responses of circuits are of significance in many applications, especially in communications and control systems. A specific application is in electric filters that block out or eliminate signals with unw anted frequencies and pass signals of the desired frequencies. Filters are used in radio, TV, and telephone systems to separate one broadcast frequency from another.

We begin this chapter by considering the frequency response of simple circuits using their transfer functions. We then consider Bode plots, which are the industry-standard w ay of presenting frequenc y response. We also consider series and parallel resonant circuits and encounter important concepts such as resonance, quality f actor, cutoff frequency, and bandwidth. We discuss different kinds of filters and network scaling. In the last section, we consider one practical application of resonant circuits and two applications of filters.