If R1 is increased in an inverting amplifier, the circuit gain and bandwidth

If R1 is increased in an inverting amplifier, the circuit gain and bandwidth

• A. Gain decreases; Bandwidth increases
• B. Gain increases; Bandwidth decreases
• C. Both increase
• D. Both decrease

Answer: (A)

In an inverting amplifier, the closed-loop gain is set by the ratio of the feedback resistor to the input resistor: Av ≈ -Rf / R1. So if you increase the input resistor R1 while keeping Rf fixed, the magnitude of the gain |Av| decreases. The bandwidth of a real op-amp in a closed loop is tied to its gain-bandwidth product: f_cl ≈ GBWP / |Av|. When |Av| decreases, the closed-loop bandwidth increases. Put together, increasing R1 lowers the gain but widens the bandwidth, which corresponds to the option stating gain decreases and bandwidth increases.

In an inverting amplifier, the closed-loop gain is set by the ratio of the feedback resistor to the input resistor: Av ≈ -Rf / R1. So if you increase the input resistor R1 while keeping Rf fixed, the magnitude of the gain |Av| decreases. The bandwidth of a real op-amp in a closed loop is tied to its gain-bandwidth product: f_cl ≈ GBWP / |Av|. When |Av| decreases, the closed-loop bandwidth increases. Put together, increasing R1 lowers the gain but widens the bandwidth, which corresponds to the option stating gain decreases and bandwidth increases.