What is the phase margin?

In electronic amplifiers, the phase margin (PM) is the difference between the phase, measured in degrees, and 180°, for an amplifier's output signal (relative to its input), as a function of frequency. read more

Phase margin and its important companion concept, gain margin, are measures of stability in closed-loop, dynamic-control systems. Phase margin indicates relative stability, the tendency to oscillate during its damped response to an input change such as a step function. read more

Similarly, the phase margin is the difference between the phase of the response and –180° when the loop gain is 1.0. The frequency Wpm at which the magnitude is 1.0 is called the unity-gain frequency or gain crossover frequency. read more

Phase Margin = +P + 180 degrees Now, to check your understanding, let's solve for the Gain and Phase Margin for both the blue and red transfer functions plotted above. (Note that the BLUE TF was the one shown on the previous page, which we found to be unstable when we 'closed the loop'. read more