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Chapter 7: Frequency Response and Bode Plots

By Steven T. Karris
From Circuit Analysis II with MATLAB Applications

This chapter discusses frequency response in terms of both amplitude and phase. This topic will enable us to determine which frequencies are dominant and which frequencies are virtually suppressed. The design of electric filters is based on the study of the frequency response. We will also discuss the Bode method of linear system analysis using two separate plots; one for the magnitude of the transfer function, and the other for the phase, both versus frequency. These plots reveal valuable information about the frequency response behavior.

Note

Throughout this text, the common (base 10) logarithm of a number x will be denoted as log( x) while its natural (base e) logarithm will be denoted as ln( x). However, we should remember that in MATLAB the log( x) function displays the natural logarithm, and the common (base 10) logarithm is defined as log10(x).

7.1 Decibels

The ratio of any two values of the same quantity (power, voltage or current) can be expressed in decibels (dB). For instance, we say that an amplifier has 10 dB power gain or a transmission line has a power loss of 7 dB (or gain ?7 dB). If the gain (or loss) is 0 dB, the output is equal to the input. We should remember that a negative voltage or current gain A V or A I indicates that there is a 180 phase difference between the input and the...

Copyright Orchard Publications 2003 under license agreement with Books24x7
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Topics of Interest
This chapter begins with the interactions between electric circuits and changing magnetic fields. It defines self and mutual inductances, flux linkages, induced voltages, the dot convention, Lenz's... (Read More)
This chapter discusses frequency response in terms of both amplitude and phase. This topic will enable us to determine which frequencies are dominant and which frequencies are virtually suppressed. (Read More)
2.19   THE DECIBEL UNIT Optical power amplitude, amplifier gain, power attenuation, optical loss, and power may be provided in units of decibels (dB). The decibel unit for power is defined as... (Read More)
Overview Decibels are used to specify ratios of powers and voltages in a logarithmic fashion. Absolute levels can also be specified via suitable reference values. Decibels are commonly used for gain... (Read More)
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