| Electronics > Beginners |
| Hi, How can i determine the cut-off frequency from this op amp graph ? |
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| rstofer:
Wimberleytech gave you a combined graph above. What you have is a pair of graphs, one for a gain of 100 and one for a gain of 10. It should be pretty easy to graph a gain of 20, or 30, or whatever. You know the outer edge of the gain-bandwidth product. That's the sloping line. Pick a gain, get a bandwidth. I pointed out that the sharp corners don't occur in the real world and, at the cutoff frequency, the output would be 3 dB down or 70.7% of the original value. The Wiki I linked shows you that the corner is rounded and, in fact the curve passes through the point that is 3 dB down or 70.7% of the original value. Look at the graph in the Wiki an notice how it is curved. We get the sharp corners when we approximate the response manually then sketch in the curve to fit. These are really just approximations, the only real response curve is obtained with a network analyzer like the tool in Digilent Waveforms for the Analog Discovery 2. Here a signal generator sweeps the frequency spectrum and the analog input is used to compute the graph. |
| rstofer:
Here's another documented related specifically to gain-bandwidth product. Note the definition for cutoff frequency https://en.wikipedia.org/wiki/Gain%E2%80%93bandwidth_product |
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