This op-amp calculator relates closed-loop gain to bandwidth using the gain-bandwidth product, so you can see how much usable bandwidth a given gain leaves you — and design amplifier stages that actually deliver the response you expect.
The gain-bandwidth trade-off
An op-amp's gain-bandwidth product (GBW) is roughly constant: gain × bandwidth equals a fixed figure quoted on the datasheet. So the more gain you ask a single stage for, the less bandwidth it has. At a gain of 10 an amplifier with a 1 MHz GBW reaches 100 kHz; at a gain of 100 it only reaches 10 kHz. The calculator works any of these out from the other two so you can check a stage will pass the frequencies you need.
This is why high-gain, high-bandwidth designs use several modest-gain stages in cascade rather than one big stage — splitting the gain keeps each stage's bandwidth comfortable. The calculator helps you plan how to divide the gain.
Designing a stage
Set the closed-loop gain with the feedback resistors, then use the GBW to confirm the resulting bandwidth covers your signal. If it falls short, reduce the per-stage gain and add a stage, or choose a faster op-amp with a higher GBW. Allow margin: response begins rolling off before the calculated bandwidth, so design for headroom above your highest frequency of interest.
An op-amp with a 1 MHz gain-bandwidth product is set for a gain of 20.
- Bandwidth = GBW ÷ gain.
- Bandwidth = 1,000,000 ÷ 20 = 50,000 Hz.
At a gain of 20, the stage has about 50 kHz of bandwidth — design with margin above your signal.
