QB_PH_SEC8_021: Operational Amplifiers & Analog Circuits

An ideal operational amplifier connected with negative feedback as a voltage follower (buffer) has

Correct Answer

### Step-by-Step Derivation & Verification: 1. **Circuit Topology**: Output terminal is hardwired directly to the inverting terminal (100% negative feedback, $\beta = 1$), while input signal is applied to non-inverting terminal. 2. **Closed-Loop Gain**: $A_v = \frac{A}{1 + A\beta} = \frac{A}{1 + A} \to 1 \quad (\text{as } A \to \infty)$ $V_{\text{out}} = V_{\text{in}}$ 3. **Terminal Impedance Characteristics**: - Input resistance: $R_{\text{in, closed}} = R_{\text{in}}(1 + A\beta) \to \infty$ (Infinite) - Output resistance: $R_{\text{out, closed}} = \frac{R_{\text{out}}}{1 + A\beta} \to 0$ (Zero) 4. **Conclusion**: Gain of 1, infinite input impedance, zero output impedance. Option (A) is correct.