According to Bode stability criterion, a system is unstable, if the open loop frequency response exhibits an amplitude ratio exceeding unity at frequency for which phase lag is_________________?
Correct answer: D. 180°
- A. 0°
- B. 45°
- C. 90°
- D. 180°
Explanation
At a phase lag of 180°, negative feedback effectively becomes positive feedback; if the open-loop gain is then greater than unity, disturbances grow instead of decaying. This is the Bode instability condition.
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