Information AboutBode Plot |
| CATEGORIES ABOUT BODE PLOT | |
| signal processing | |
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A Bode plot, named for Hendrik Wade Bode , is usually a combination of a Bode magnitude plot and Bode phase plot: A Bode magnitude plot is a graph of Log magnitude against log Frequency often used in Signal Processing to show the Transfer Function or Frequency Response of an LTI system. It makes multiplication of magnitudes a simple matter of adding distances on the graph, since : The Bode plot describes the output response of a frequency-dependent system for a normalised input. The magnitude axis of the Bode plot is often converted directly to Decibel s. A Bode phase plot is a graph of phase against log frequency, usually used in conjunction with the magnitude plot, to evaluate how much a frequency will be Phase-shifted . For example a signal described by: ''A''sin(ω''t'') may be attenuated but also phase-shifted. If the system attenuates it by a factor ''x'' and phase shifts it by −Φ the signal out of the system will be (''A''/''x'') sin(ω''t'' − Φ). The phase shift Φ is generally a function of frequency. The magnitude and phase Bode plots can seldom be changed independently of each other — if you change the amplitude response of the system you will most likely change the phase characteristics as well and vice versa. For minimum-phase systems the phase and amplitude characteristics can be obtained from each other with the use of the Hilbert Transform . If the transfer function is a rational function, then the Bode plot can be drawn quite easily as it is possible to approximate it with straight lines. These asymptotic approximations are useful because they can be drawn by hand following a few simple rules. Simple plots can even be predicted without drawing them. EXAMPLE A Lowpass RC Filter , for instance has the following frequency response: : The Cutoff Frequency point ''f''c (in Hertz ) is at the frequency :. The line approximation of the Bode plot consists of two lines:
These two lines meet at the Cutoff Frequency . From the plot it can be seen that for frequencies well below the Cutoff Frequency the circuit has an attenuation of 0dB, the filter does not change the amplitude. Frequencies above the Cutoff Frequency are attenuated - the higher the frequency, the higher the attenuation. SEE ALSO EXTERNAL LINKS
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