Which statement is false? an inverting summing amplifier does not alter the polarity of the summed voltages

Which statement is false? an inverting summing amplifier does not alter the polarity of the summed voltages

• A. An inverting summing amplifier sums multiple inputs.
• B. An inverting summing amplifier does not alter the polarity of the summed voltages.
• C. An inverting summing amplifier's output is inverted relative to inputs.
• D. The circuit uses negative feedback.

Answer: (B)

Inverting summing amplifiers produce an inverted sum of their inputs because the signals are applied to the inverting input and negative feedback forces that node to a virtual ground. Each input resistor feeds current into the summing junction, and the feedback resistor converts the total current into an output voltage that has the opposite sign to the inputs. For an ideal op-amp, the output relationship is Vout = -Rf Σ(Vi/Ri), so any positive input voltages yield negative outputs, and the polarity is flipped. This is why the statement claiming the polarity is not altered is false. The other facts are correct: it can sum multiple inputs through separate resistors, the output is inverted relative to the inputs, and the circuit relies on negative feedback to set the gain and keep the operation linear.

Inverting summing amplifiers produce an inverted sum of their inputs because the signals are applied to the inverting input and negative feedback forces that node to a virtual ground. Each input resistor feeds current into the summing junction, and the feedback resistor converts the total current into an output voltage that has the opposite sign to the inputs. For an ideal op-amp, the output relationship is Vout = -Rf Σ(Vi/Ri), so any positive input voltages yield negative outputs, and the polarity is flipped.

This is why the statement claiming the polarity is not altered is false. The other facts are correct: it can sum multiple inputs through separate resistors, the output is inverted relative to the inputs, and the circuit relies on negative feedback to set the gain and keep the operation linear.