"In electronic amplifiers, the phase margin (PM) is the difference between the phase, measured in degrees, and 180\u00B0, for an amplifier's output signal (relative to its input), as a function of frequency. Typically the open-loop phase lag (relative to input) varies with frequency, progressively increasing to exceed 180\u00B0, at which frequency the output signal becomes inverted, or antiphase in relation to the input."@en .