Op-amp feedback resistors: in standard inverting and noninverting operational-amplifier configurations, the pair of resistors labeled Rf (feedback) and Ri (input/reference) primarily control which aspects of circuit behavior?

Introduction / Context:
Most op-amp applications rely on external resistor networks to define closed-loop behavior. The two most recognizable elements are Ri (the input or reference resistor) and Rf (the feedback resistor). Understanding their roles allows accurate prediction of gain, linearity, input/output impedance, and stability boundaries.

Given Data / Assumptions:

• Linear operation within the op-amp’s bandwidth and slew limits.
• Classic inverting and noninverting topologies using Ri and Rf.
• Negative feedback is used to set closed-loop gain.

Concept / Approach:
In the inverting amplifier, the closed-loop gain is V_out / V_in = −Rf / Ri. In the noninverting amplifier, V_out / V_in = 1 + Rf / Ri. In both cases, the ratio Rf/Ri establishes the voltage gain while simultaneously returning a portion of the output to the input with negative sign—this is negative feedback. Power gain is a by-product of voltage gain with available output current and supply rails; “open-loop gain” is an intrinsic op-amp parameter (A_ol) not directly set by Rf and Ri.

Step-by-Step Solution:

Verification / Alternative check:
Reducing Rf lowers |gain| in the inverting case; increasing Rf raises it—demonstrating direct control of voltage gain. The loop polarity (through the inverting input) ensures negative feedback, stabilizing the amplifier and reducing distortion within bandwidth limits.

Why Other Options Are Wrong:

• Positive feedback and current gain: positive feedback is not used in linear op-amp amplifiers; “current gain” is not the primary parameter here.
• Negative feedback and power gain: power gain depends on load and output stage limits; Rf/Ri chiefly set voltage gain.
• Open and closed loop gain: open-loop gain is internal (A_ol), not chosen by these resistors.
• Bias stability only: biasing is affected but not the primary function of Rf/Ri.

Common Pitfalls:
Assuming Rf and Ri influence open-loop gain; overlooking bandwidth and phase margin that constrain usable closed-loop gain at higher frequencies.

Final Answer:
Negative feedback and voltage gain