Which statement about the summing amplifier is true?

Which statement about the summing amplifier is true?

• A. The summing action produces an output proportional to the sum of inputs, scaled by resistor ratios.
• B. It cannot handle more than two inputs.
• C. The output is inverted relative to each input.
• D. The circuit requires no feedback.

Answer: (D)

In a summing amplifier, multiple input voltages are connected through their own resistors to the inverting input of an op-amp, with a resistor from output back to that input providing negative feedback. This feedback keeps the inverting node near ground (a virtual ground) and forces the output to adjust so that the sum of the input currents flows through the feedback path. The result is that the output voltage is proportional to the algebraic sum of the inputs, each scaled by its input resistor, with an overall negative sign: Vout = -Rf (V1/R1 + V2/R2 + ...). This relies on feedback to establish the gain and the virtual ground condition; without feedback, the op-amp would saturate and the summing relationship would not hold. The circuit can handle many inputs, and the contribution of each input is inverted in the total output, so the overall behavior is a scaled, inverted sum of all inputs.

In a summing amplifier, multiple input voltages are connected through their own resistors to the inverting input of an op-amp, with a resistor from output back to that input providing negative feedback. This feedback keeps the inverting node near ground (a virtual ground) and forces the output to adjust so that the sum of the input currents flows through the feedback path. The result is that the output voltage is proportional to the algebraic sum of the inputs, each scaled by its input resistor, with an overall negative sign: Vout = -Rf (V1/R1 + V2/R2 + ...). This relies on feedback to establish the gain and the virtual ground condition; without feedback, the op-amp would saturate and the summing relationship would not hold. The circuit can handle many inputs, and the contribution of each input is inverted in the total output, so the overall behavior is a scaled, inverted sum of all inputs.