Exam-style question
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Why does a real op‑amp’s output become distorted when the input signal frequency is high, even if the gain is still within the specified range? Discuss the combined effects of bandwidth and slew rate.
Model answer
What a good answer should say
- At high frequencies the op‑amp’s open‑loop gain has already dropped, so the closed‑loop gain is reduced.
- The required output slope for a given amplitude increases with frequency.
- If this slope exceeds the op‑amp’s slew rate, the output cannot change quickly enough, producing a clipped or rounded waveform.
- Thus distortion occurs because the bandwidth limits the achievable gain and the slew rate limits the maximum output swing per unit time.
Explanation
Why this works
This answer shows the student can analyse how both bandwidth and slew rate contribute to distortion, explaining the interaction between frequency, gain, and output rate. It tests the objective by requiring a qualitative explanation of two interrelated limitations.
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