Sign In

The Bode plot is an essential tool in control system analysis, mapping the frequency response of a system through a magnitude plot and a phase plot, both against a logarithmic frequency axis. To construct a Bode plot, consider the transfer function H(ω):

Equation 1

It has constant gain, zeros, and poles. After normalizing the transfer function is written as:

Equation 2

Each term in this normalized function affects the Bode plot distinctly. The term 10jω has a constant gain of 10 and zero at origin jω. Each simple pole term (1+jω/ωi) introduces a breakpoint or corner frequency ωi. The zero's positive slope is evident from the origin, while the poles' negative slopes commence at their corner frequencies, ω=2 and ω=10 respectively.

Equation 3

Equation 4

Once the individual contribution of each term is identified, the overall Bode plot can be constructed. This involves superposing the slopes and phase changes of each factor. At low frequencies, the magnitude plot starts at 20 dB (since 20log10(10) =20) and maintains a flat response up to the first corner frequency. The phase plot starts at 90° due to the zero at the origin and begins its descent before the first corner frequency.

The magnitude plot's slope will change at each corner frequency, decreasing by 20 dB/decade at ω=2 and again at ω=10. Correspondingly, the phase plot will bend downwards, approaching -90° at a frequency much higher than ω=10.

Finally, the asymptotic Bode plot, which consists of these straight lines, can be adjusted to approximate the actual frequency response more closely. This involves adding a smooth curve intersecting the asymptotic plot at each corner frequency, typically resulting in a slight overshoot near the corner frequencies, known as peaking.

Tags
Bode PlotControl System AnalysisFrequency ResponseTransfer FunctionMagnitude PlotPhase PlotLogarithmic FrequencyCorner FrequencyPolesZerosGainBreakpointSuperposing SlopesAsymptotic Bode PlotPeaking

From Chapter 9:

article

Now Playing

9.7 : Bode Plots Construction

Frequency Response

67 Views

article

9.1 : Network Function of a Circuit

Frequency Response

105 Views

article

9.2 : Frequency Response of a Circuit

Frequency Response

71 Views

article

9.3 : Gain

Frequency Response

53 Views

article

9.4 : Bode Plots

Frequency Response

74 Views

article

9.5 : Transfer function and Bode Plots-I

Frequency Response

76 Views

article

9.6 : Transfer function and Bode Plots-II

Frequency Response

70 Views

article

9.8 : Series Resonance

Frequency Response

42 Views

article

9.9 : Characteristics of Series Resonant Circuit

Frequency Response

78 Views

article

9.10 : Parallel Resonance

Frequency Response

62 Views

article

9.11 : Frequency Response of Op Amp Circuits

Frequency Response

92 Views

article

9.12 : Passive Filters

Frequency Response

67 Views

article

9.13 : Active Filters

Frequency Response

110 Views

article

9.14 : Scaling

Frequency Response

118 Views

article

9.15 : Design Example

Frequency Response

48 Views

JoVE Logo

Privacy

Terms of Use

Policies

Research

Education

ABOUT JoVE

Copyright © 2025 MyJoVE Corporation. All rights reserved