All courses › Control Engineering › Bode Plot

Bode Plot

A Bode plot shows how a system's gain (in decibels) and phase change with frequency, both plotted against a logarithmic frequency axis. A single pole gives an asymptote that falls 20 dB per decade above the corner frequency, while a zero gives a matching rise. This lets you read off the system's behavior without computing the response in the time domain.

∣G∣dB=20log⁡10∣G∣|G|_{dB}=20\log_{10}|G|gain in decibels
ωc=1/τ\omega_c=1/\taucorner frequency of a single pole

Symbols

∣G∣dB|G|_{dB}gain in decibelsdB
ωc\omega_ccorner frequencyrad/s

Example

∣G∣=0.1|G|=0.1:

∣G∣dB=20log⁡10(0.1)=−20|G|_{dB}=20\log_{10}(0.1)=-20 dB.

A single pole gives −20-20 dB/decade above the corner frequency; a zero gives +20+20 dB/decade.
Practise frequency analysis for free →

← Ziegler-Nichols · Phase Margin →

Part of Control Engineering: Frequency analysis.