How to understand Bode plot or Bode diagram
The BODE plot is a graphical representation of the frequency-dependent gain and phase of a circuit (amplifier, filter, control system,...).
In this context, there are two fundamental cases as far as a system with feedback is concerned:
(1) BODE-Diagram for the closed-loop system. Here you can see if the sysytem can meet your requirements concerning gain, bandwidth, phase shift, attenuation (for filters),...
(2) BODE-Diagram for the open-loop system (open the loop at a suitable point and find the gain and the phase for all pars/blocks within the whole loop in series).
This function is called &quot;loop gain&quot;. Now you can apply the well-known stability criterion. For this purpose, you must find the phase shift for the frequency where the magnitude of the loop gain is 0 dB. From this analysis you can derive the stability margin, which tells you if the closed-loop will be stable and how many &quot;margin&quot; the closed-loop system has until it will become unstable.,