If an op-amp has a unity-gain bandwidth of 1 MHz and you design a closed-loop gain of 5, what is the approximate closed-loop bandwidth?

If an op-amp has a unity-gain bandwidth of 1 MHz and you design a closed-loop gain of 5, what is the approximate closed-loop bandwidth?

• A. 200 Hz.
• B. 20 kHz.
• C. 200 kHz.
• D. 2 MHz.

Answer: (C)

Op-amps with a dominant pole have a roughly constant gain–bandwidth product. That means the closed-loop bandwidth is about the unity-gain bandwidth divided by the closed-loop gain. Here the unity-gain bandwidth is 1 MHz, and the closed-loop gain is 5, so the bandwidth is approximately 1 MHz / 5 = 0.2 MHz, i.e., 200 kHz. This holds under the usual single-pole model and when the amplifier stays within its linear range; real devices may shift a bit, but 200 kHz is the standard estimate.

Op-amps with a dominant pole have a roughly constant gain–bandwidth product. That means the closed-loop bandwidth is about the unity-gain bandwidth divided by the closed-loop gain. Here the unity-gain bandwidth is 1 MHz, and the closed-loop gain is 5, so the bandwidth is approximately 1 MHz / 5 = 0.2 MHz, i.e., 200 kHz. This holds under the usual single-pole model and when the amplifier stays within its linear range; real devices may shift a bit, but 200 kHz is the standard estimate.