GATE 2017 EE (EE2) – Question 48

Analog and Digital Electronics · Operational amplifiers: characteristics and applications · 2 marks · Multiple choice

The op-amp in the circuit is ideal. Which relation is true?

Show answer and explanation

Correct answer: (C) $v_O=2.5v_S$

Explanation

The equal 2R input divider gives V+=vS/2, so feedback sets the inverting node to the same voltage vS/2.

Let the junction of the three upper R resistors be Vx. KCL at the inverting node gives $V_-/R+(V_--V_x)/R=0$, hence Vx=2V−=vS.

At Vx, KCL gives $(V_x-V_-)+V_x+(V_x-v_O)=0$. Therefore $v_O=3V_x-V_-=3v_S-v_S/2=$ **2.5vS, C**.

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