Phase Margin

What is Phase Margin?

The amount of additional phase lag, measured at the frequency where open-loop gain crosses 0 dB, that a stable feedback system could absorb before being pushed to instability. Together with gain margin it forms the standard pair of frequency-domain stability checks, with designers typically targeting 45–60 degrees for a well-damped response.

The five clues

Engineerdle #38 described Phase Margin with five clues, revealed one at a time from hardest to most direct. Each clue points at a different property of the concept.

1. 01Gain margin's partner, measuring a different kind of safety buffer.
2. 02It's measured at the frequency where gain has dropped to exactly 0 dB.
3. 03It quantifies how much extra phase lag the loop could absorb before going unstable.
4. 04A healthy design usually targets somewhere around 45 to 60 degrees of it.
5. 05The amount of additional phase lag, at the gain crossover frequency, that would push a stable system to instability.

More Control Systems concepts

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• OvershootPuzzle #43
• Laplace TransformPuzzle #33