Op-amp functional blocks — name the circuit: A circuit whose output equals the algebraic sum (with signs and scaling set by resistors) of multiple input signals is called a(n) ______.

Introduction / Context:
An extremely common operational-amplifier (op-amp) building block is the circuit that adds several input signals together to produce an output equal to their algebraic sum (possibly scaled and with sign inversion depending on topology). This question asks you to identify that circuit by name, which is foundational for audio mixers, sensor fusion, and analog computation.

Given Data / Assumptions:

• Multiple input signals are applied to an op-amp network.
• The output equals the algebraic sum of inputs (with gains set by resistor ratios).
• Ideal op-amp assumptions for concept: very high open-loop gain, infinite input impedance, and low output impedance.

Concept / Approach:
The classic inverting summing amplifier uses one feedback resistor Rf and several input resistors Rin_k. With negative feedback, the inverting input is held at a virtual ground, and each input contributes a current proportional to its voltage divided by its input resistor. The op-amp output develops whatever voltage is required so that the sum of currents through the feedback path balances the input currents, yielding an output proportional to the algebraic sum of inputs. A noninverting summer can also be built using scaling and buffering, but the inverting summer is most common for precise weighted addition.

Step-by-Step Solution:

Verification / Alternative check:
Textbook formulas show Vout = −Rf * (V1/R1 + V2/R2 + ...). Equal Rin values produce an equal-weight arithmetic sum (with inversion). Buffering or an extra stage can remove inversion if required, preserving the “summing” function by name.

Why Other Options Are Wrong:

• Integrator amplifier: performs time integration, not instantaneous summation of multiple channels.
• Differential amplifier: outputs a scaled difference between two inputs, not the sum of many.
• Voltage multiplier: produces a product or frequency conversion, not a sum.

Common Pitfalls:
Confusing a differential amplifier (difference) with a summing amplifier (sum), and forgetting that sign inversion is a property of the inverting summer that can be corrected by an additional inverting stage if a noninverted sum is desired.

Final Answer:
Summing amplifier.