GATE 2022 PH – Question 20
For an Op-Amp based negative feedback, non-inverting amplifier, which of the following statements are true?
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Correct answer: (A) Closed loop gain < Open loop gain; (C) Closed loop input impedance > Open loop input impedance; (D) Closed loop output impedance < Open loop output impedance
Explanation
A non-inverting amplifier with **negative voltage-series feedback** has these properties compared with the open-loop amplifier:
- **A. Closed-loop gain < open-loop gain.** True: $A_f=\dfrac{A}{1+A\beta}<A$. ✓
- **B. Closed-loop bandwidth < open-loop bandwidth.** False. The bandwidth is **larger** by the factor $(1+A\beta)$ (the gain-bandwidth product is constant).
- **C. Closed-loop input impedance > open-loop input impedance.** True: series feedback multiplies the input impedance by $(1+A\beta)$. ✓
- **D. Closed-loop output impedance < open-loop output impedance.** True: voltage feedback divides the output impedance by $(1+A\beta)$. ✓
Answer **A, C and D**.