In a summing amplifier, increasing any one input while the others are constant will primarily affect the output through which mechanism?

In a summing amplifier, increasing any one input while the others are constant will primarily affect the output through which mechanism?

• A. The resistor network ratio in the feedback path
• B. The input impedance
• C. The op-amp saturates
• D. The output becomes inverted

Answer: (A)

In a summing amplifier, the output is a weighted sum of the input voltages, with each input weighted by the ratio of the feedback resistor to its own input resistor. The op-amp keeps the inverting input at a virtual ground, so the current from each input through its resistor must flow through the feedback resistor. This makes the contribution of each input to the output proportional to -Rf/Ri for that input. Therefore, when you increase one input while others stay fixed, the output changes by ΔVout = -(Rf/Ri) · ΔVi. This shows the change is governed by the resistor network ratio in the feedback path. The other options don’t capture this mechanism: input impedance is set by the individual input resistor values and doesn’t dictate how the output scales with an input change; saturation would only happen if the output hits supply rails; inversion is a general property of the inverting configuration, not the rule that determines how a given input alters the output magnitude.

In a summing amplifier, the output is a weighted sum of the input voltages, with each input weighted by the ratio of the feedback resistor to its own input resistor. The op-amp keeps the inverting input at a virtual ground, so the current from each input through its resistor must flow through the feedback resistor. This makes the contribution of each input to the output proportional to -Rf/Ri for that input. Therefore, when you increase one input while others stay fixed, the output changes by ΔVout = -(Rf/Ri) · ΔVi. This shows the change is governed by the resistor network ratio in the feedback path.

The other options don’t capture this mechanism: input impedance is set by the individual input resistor values and doesn’t dictate how the output scales with an input change; saturation would only happen if the output hits supply rails; inversion is a general property of the inverting configuration, not the rule that determines how a given input alters the output magnitude.