Consider the circuit with an ideal OPAMP shown in the figure. Assuming V IN V CC and V REF V CC , the condition at which V OUT equals to zero is

GATE 2021 EC – Question 20

Analog Circuits · Op-amp Circuits · 1 mark · Multiple choice

Consider the circuit with an ideal OPAMP shown in the figure.

Assuming $|V_{IN}|\ll|V_{CC}|$ and $|V_{REF}|\ll|V_{CC}|$, the condition at which $V_{OUT}$ equals to zero is

$V_{IN}=V_{REF}$
$V_{IN}=0.5\,V_{REF}$
$V_{IN}=2\,V_{REF}$
$V_{IN}=2+V_{REF}$

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) $V_{IN}=V_{REF}$

Explanation

The op-amp is an inverting summer with equal resistors $R$ at the two inputs. The $V_{REF}$ source is connected with its positive terminal towards ground, so the branch applies $-V_{REF}$ to its resistor. Then $V_{OUT}=-\frac{R_F}{R}\left(V_{IN}-V_{REF}\right)$, which is zero when $V_{IN}=V_{REF}$.