Closed-loop gain from resistor ratio — A feedback amplifier has a feedback/input resistor ratio RFB/RIN = 4.6 and is driven at the noninverting (+) input with 1.7 V. Assuming a standard noninverting configuration in linear operation, what is the output voltage?
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A7.82 V
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Bsaturation
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Ccutoff
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D9.52 V
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E4.6 V
Answer
Correct Answer: 9.52 V
Explanation
Introduction:For a noninverting amplifier, the closed-loop gain depends on the feedback network ratio. Correctly mapping the stated “feedback/input resistor ratio” to the noninverting gain expression ensures accurate output predictions and avoids misinterpreting saturation or cutoff conditions when rails are not specified.
Given Data / Assumptions:
- Noninverting configuration
- RFB/RIN = 4.6
- Vin (+ input) = 1.7 V
- Ideal op-amp, linear range (supply rails wide enough)
Concept / Approach:
The closed-loop gain for the noninverting amplifier is Av = 1 + (RFB / RIN). Multiply this by the input voltage to obtain the output voltage, provided the result is within supply rails and the amplifier remains unsaturated.
Step-by-Step Solution:
Compute gain: Av = 1 + 4.6 = 5.6Compute output: Vout = Av * Vin = 5.6 * 1.7 VVout = 9.52 VAssume rails permit 9.52 V so the amplifier stays linearVerification / Alternative check:
Rearrange to check: Vin = Vout / Av = 9.52 / 5.6 = 1.7 V, confirming consistency.
Why Other Options Are Wrong:
- 7.82 V: Uses an incorrect gain factor.
- saturation / cutoff: No evidence of rail limits or biasing to force nonlinearity.
- 4.6 V: Misreads the ratio as the gain itself and ignores the “+1” term.
Common Pitfalls:
- Forgetting the “+1” in the noninverting gain formula.
- Confusing RFB/RIN with RIN/RFB.
Final Answer:
9.52 V