For a positive input, the output of an inverting amplifier is

For a positive input, the output of an inverting amplifier is

• A. The output becomes positive
• B. The output is independent of the input
• C. The output equals the input
• D. The output is negative

Answer: (D)

An inverting amplifier outputs the negative of the input, scaled by the ratio of the feedback resistor to the input resistor. With the non-inverting input tied to ground, negative feedback keeps the inverting input at a virtual ground (almost zero volts). The input signal pushes current through the input resistor into that summing node, and the output adjusts through the feedback resistor to keep the node near zero. This forces the output to swing in the opposite direction to the input, giving Vout = - (Rf/Rin) * Vin. Therefore, a positive Vin produces a negative Vout. The sign flip is the defining feature of the inverting configuration, while the magnitude depends on the resistor ratio.

An inverting amplifier outputs the negative of the input, scaled by the ratio of the feedback resistor to the input resistor. With the non-inverting input tied to ground, negative feedback keeps the inverting input at a virtual ground (almost zero volts). The input signal pushes current through the input resistor into that summing node, and the output adjusts through the feedback resistor to keep the node near zero. This forces the output to swing in the opposite direction to the input, giving Vout = - (Rf/Rin) * Vin. Therefore, a positive Vin produces a negative Vout. The sign flip is the defining feature of the inverting configuration, while the magnitude depends on the resistor ratio.