Log plots of gain and phase against frequency.
Bode plots show gain in dB (20·log10 of gain magnitude) and phase against log frequency using straight-line asymptotes. A pole contributes -20 dB/dec past its corner, a zero +20 dB/dec. They quickly reveal bandwidth, gain and stability margins.
A single-pole system has -3 dB and -45° at its corner.
Bode plots show gain and phase over a wide frequency range on a log scale, so they are the standard tool for stability and filter design.
Log plots of gain and phase against frequency.
Bode plots show gain and phase over a wide frequency range on a log scale, so they are the standard tool for stability and filter design.
Frequencies and gains span many decades, and a log scale makes straight-line approximations possible and shows the shape of the response clearly.
They approximate the response with straight segments that change slope at corner frequencies, which allows fast sketching of the plot.
Typical applications include checking the gain margin of a feedback amplifier from its Bode plot, reading the cutoff frequency of an audio filter and designing a compensator for a motor speed loop.
Study "Filters" first (topic 47 of 106 in Electrical Engineering). It covers the groundwork this topic builds on.
Corner frequencies. Phase changes 90° per pole. Compose by adding plots.
A single-pole system has -3 dB and -45° at its corner.
The next topic is "Two-port networks", which builds directly on this one.
It is classed as Intermediate in Electrical Engineering (topic 48 of 106). It is an intermediate topic. Work through the beginner topics in Electrical Engineering first.
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