Gain-Bandwidth product question

[bitrex]

If I have an op-amp with say, a hypothetical bandwidth of 1 MHz, and I use it in a configuration where I have a gain of 10, I know that I will only have unity gain at an input frequency of 100kHz. What I am wondering is how I go about calculating what the effective cutoff frequency is, i.e. where the gain is down -3dB? Thanks!

 

[uart]

.. and I use it in a configuration where I have a gain of 10, I know that I will only have unity gain at an input frequency of 100kHz. ...

No that's incorrect. So long as the other poles (apart from the dominant pole that sets the 1MHz GBWP) are above 100kHz then 100Khz will indeed be a very good approximation to the actual -3dB frequency.

 

[oswaler]

The effective cutoff frequency in this scenario can be calculated using the gain-bandwidth product formula, which states that the product of the gain and bandwidth of an op-amp is constant. In this case, the gain-bandwidth product would be 10 MHz (10 x 1 MHz). So, to find the effective cutoff frequency, we can rearrange the formula to solve for bandwidth: bandwidth = gain-bandwidth product / gain. Plugging in the values, we get a bandwidth of 1 MHz (10 MHz / 10). This means that the effective cutoff frequency, where the gain is down -3dB, would be 1 MHz. I hope this helps answer your question!