Explain the trade-off between closed-loop gain and bandwidth and how GBW constrains the relationship.

Explain the trade-off between closed-loop gain and bandwidth and how GBW constrains the relationship.

• A. As the closed-loop gain increases, the bandwidth increases; the product of closed-loop gain and bandwidth is not limited by GBW.
• B. As the closed-loop gain increases, the bandwidth decreases; the product of closed-loop gain and bandwidth is limited by GBW.
• C. The bandwidth is independent of closed-loop gain and GBW.
• D. GBW only affects open-loop behavior and has no impact on closed-loop systems.

Answer: (B)

The trade-off being tested is that an op-amp’s closed-loop bandwidth is limited by its gain-bandwidth product. A real amplifier has a finite speed set by an internal dominant pole, so when you close the loop to set a certain gain, the usable frequency range where that gain holds is limited. For a given device, the closed-loop bandwidth is approximately GBW divided by the closed-loop gain. That means increasing the closed-loop gain reduces the bandwidth, while decreasing the gain broadens the bandwidth. The product of closed-loop gain and bandwidth stays roughly constant and cannot exceed the GBW of the device. For example, if GBW is about 1 MHz, a closed-loop gain of 10 gives roughly 100 kHz bandwidth, while a gain of 2 gives about 500 kHz bandwidth. This is why higher gain comes at the cost of narrower bandwidth, and the GBW sets the limit on how large the product can be.

The trade-off being tested is that an op-amp’s closed-loop bandwidth is limited by its gain-bandwidth product. A real amplifier has a finite speed set by an internal dominant pole, so when you close the loop to set a certain gain, the usable frequency range where that gain holds is limited. For a given device, the closed-loop bandwidth is approximately GBW divided by the closed-loop gain. That means increasing the closed-loop gain reduces the bandwidth, while decreasing the gain broadens the bandwidth. The product of closed-loop gain and bandwidth stays roughly constant and cannot exceed the GBW of the device. For example, if GBW is about 1 MHz, a closed-loop gain of 10 gives roughly 100 kHz bandwidth, while a gain of 2 gives about 500 kHz bandwidth. This is why higher gain comes at the cost of narrower bandwidth, and the GBW sets the limit on how large the product can be.