10.1: Introduction

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This chapter introduced two related items; the decibel and Bode plots. The decibel measurement scheme is in wide use, particularly in the fields of audio and communications. We will be examining its advantages over the ordinary system of measurement used up to now and how to convert values of one form into the other. One of the more important parameters of a circuit is its frequency response, that is, the way in which the circuit responds to input signals over a range of frequencies. While we have investigated this to some extent in prior work, in this chapter we shall take it to its logical conclusion, namely the Bode plot. A Bode plot is, in fact, a pair of plots; one of relative signal magnitude or gain with respect to frequency and a second detailing the phase response with respect to frequency. Bode plots are of particular importance in the study of circuits such as amplifiers and filters, as well as in systems that make use of negative feedback. The gain magnitude plot makes use of a decibel scale and thus it makes sense to begin our study looking at the decibel system: specifically how it is defined and its practical use.