To increase the circuit gain, you should decrease the value of Rin.

To increase the circuit gain, you should decrease the value of Rin.

• A. Decrease Rin
• B. Increase Rin
• C. Decrease Rf
• D. Increase Rf

Answer: (A)

In an inverting op-amp, the closed-loop gain is set by the ratio -Rf/Rin. So if you decrease Rin while keeping Rf fixed, that ratio grows in magnitude, increasing the gain (and the sign remains negative). Conceptually, the op-amp keeps the summing junction at virtual ground, so a smaller Rin means more input current for a given Vin, which must be carried through Rf, yielding a larger output voltage in the opposite direction. Increasing Rin would reduce the gain, decreasing Rf would reduce the gain, and increasing Rf would increase the gain.

In an inverting op-amp, the closed-loop gain is set by the ratio -Rf/Rin. So if you decrease Rin while keeping Rf fixed, that ratio grows in magnitude, increasing the gain (and the sign remains negative). Conceptually, the op-amp keeps the summing junction at virtual ground, so a smaller Rin means more input current for a given Vin, which must be carried through Rf, yielding a larger output voltage in the opposite direction. Increasing Rin would reduce the gain, decreasing Rf would reduce the gain, and increasing Rf would increase the gain.