Question

Find the output of inverting amplifier?

(a) Vo  = AVin

(b) Vo  = -AVin

(c) Vo  = -A(Vin1– Vin2)

(d) None of the mentioned

I have been asked this question during an online exam.

Enquiry is from Open Loop Op-Amp Configuration in division Operational Amplifier Characteristics of Linear Integrated Circuits

Answer 1

The correct answer is:

(b) Vo=−AVinV_o = -A V_{in}Vo​=−AVin​

Explanation:

In an inverting amplifier configuration using an operational amplifier, the output voltage is the negative amplified version of the input voltage. The relationship is given by:

Vo=−AVinV_o = -A V_{in}Vo​=−AVin​

Where:

• VoV_oVo​ is the output voltage.
• $A$ is the gain of the op-amp (which could be set by external resistors in the circuit).
• VinV_{in}Vin​ is the input voltage.

The negative sign indicates that the output is inverted (180° out of phase) compared to the input signal. The gain $A$ is determined by the ratio of the feedback resistor and the input resistor in the circuit.

Why not the other options?

• (a) Vo=AVinV_o = A V_{in}Vo​=AVin​: This formula applies to a non-inverting amplifier, where the output is in phase with the input.
• (c) Vo=−A(Vin1−Vin2)V_o = -A(V_{in1} - V_{in2})Vo​=−A(Vin1​−Vin2​): This applies to a differential amplifier, where the output depends on the difference between two input voltages.
• (d) None of the mentioned: Incorrect because option (b) is the correct formula for an inverting amplifier.