The inverting unity-gain amplifier has a gain equal to which ratio, and what happens to the input signal?

The inverting unity-gain amplifier has a gain equal to which ratio, and what happens to the input signal?

• A. Gain of -R3/R1, the signal is inverted
• B. Gain of +R3/R1, the signal is non-inverted
• C. Gain of -R3/R1, the signal is non-inverted
• D. Gain of +R3/R1, the signal is inverted

Answer: (A)

In an inverting amplifier, the output is the input scaled by a negative factor equal to the ratio of the feedback resistor to the input resistor: Vout/Vin = -Rf/Rin. In a unity-gain setup, these two resistors are equal, so the magnitude is 1 and the sign is negative. Therefore, the gain is -R3/R1 and the input signal is inverted. If R3 = R1, the gain is -1, giving an inverted output with the same amplitude as the input. Positive gains would imply no inversion, which doesn’t describe this topology.

In an inverting amplifier, the output is the input scaled by a negative factor equal to the ratio of the feedback resistor to the input resistor: Vout/Vin = -Rf/Rin. In a unity-gain setup, these two resistors are equal, so the magnitude is 1 and the sign is negative. Therefore, the gain is -R3/R1 and the input signal is inverted. If R3 = R1, the gain is -1, giving an inverted output with the same amplitude as the input. Positive gains would imply no inversion, which doesn’t describe this topology.