For design of control systems, any of the three types of plots [ Bode, Nyquist, Nichols ] can be used to infer closed-loop stability and stability margins ( gain and phase margins ) from the open-loop frequency response, provided that for the Bode analysis the phase-versus-frequency plot is included.
22.
OL ( " f " 0 dB ) > & minus; 180? the instability condition cannot be met at any frequency ( because its magnitude is going to be 180 ), and the distance of the phase at " f " 0 dB in degrees above & minus; 180?is called the " phase margin ".
23.
Comparing the labeled points in Figure 6 and Figure 7, it is seen that the unity gain frequency " f " 0 dB and the phase-flip frequency " f " 180 are very nearly equal in this amplifier, " f " 180 H " " f " 0 dB H " 3.332 kHz, which means the gain margin and phase margin are nearly zero.
