What is the significance of gain-bandwidth product in operational amplifiers?

• A. The product of closed-loop gain and bandwidth remains constant for a given op-amp; determines achievable bandwidth at a chosen gain.
• B. It describes the output impedance.
• C. It determines input offset voltage.
• D. It is only relevant for power amplifiers.

Answer: (A)

Gain-bandwidth product shows how an op-amp trades gain for speed. For a typical op-amp with a dominant pole, the closed-loop gain and the bandwidth multiply to about a constant value. In other words, increasing the closed-loop gain reduces the bandwidth proportionally, and decreasing the gain increases the bandwidth by the same factor. This lets you predict performance: the usable bandwidth at a chosen gain is roughly the op-amp’s GBP divided by that gain. For example, if an op-amp has a GBP of 10 MHz and you configure it for a gain of 5, you’d expect about 2 MHz of bandwidth. This concept is crucial for selecting an amplifier that must provide both a certain gain and a enough speed for the signal. It’s not about output impedance or input offset voltage, and it’s a general consideration, not limited to power amplifiers.