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Electronics Engineering QUESTION #11745
Question 1
A Bode plot of a feedback amplifier shows the open-loop gain crossing 0 dB at 1 MHz with a phase of $-140°$. The phase margin is:
  • $40°$✔️
  • $-40°$
  • $140°$
  • $220°$
Correct Answer Explanation
Phase margin $= 180° + \phi_{crossover} = 180° + (-140°) = \mathbf{40°}$. The phase margin is positive (40°), indicating a stable system. A phase margin of 45° is typically considered the minimum for good stability with acceptable transient response. Phase margin < 0° indicates instability (oscillation).