Phase Margin Rule of Thumb

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Phase Margin Rule of Thumb
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Phase Margin Block Diagram
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1 Phase Margin Rule of Thumb

The phase margin is one of the robustness measures of a closed loop system under control. A low phase margin will lead to undesirable oscillations in the step response.

The phase margin can be determined from a:

  • Bode Plot of the open loop transfer function magnitude crosses 0 dB
  • Nichols Plot where the open loop transfer function magnitude crosses 0 dB

1.1 Minimum Recommended Phase Margin

A good rule of thumb for the phase margin is

Table 1: Minimum Phase Margin Recommendations
Application Minimum Phase Margin (deg)

Tracking

40

Please feel free to add the recommended minimum phase margin for the applications you are familiar with.