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Gain Margin

The gain margin is the gain in dB above or below the 0 dB line at the phase crossover frequency. If an open-loop response has many phase crossover frequencies, then the gain margin is the worst and lowest absolute value of all the gain margins. In Figure: Margins and Axis Stability, the frequency at which the gain margin is calculated is highlighted with the purple cursor.

A low absolute value for the gain margin usually causes high-frequency noise and robustness that is not sufficient to variations in load. If you specify a gain margin of 8 dB, it balances performance and robustness satisfactorily.

Tip: If the worst gain margin occurs at a low-frequency where the open-loop magnitude is positive, the frequency response module shows you a negative value for the gain margin. Always use the absolute value of the gain margin when you examine axis stability.