Electronic – Operational Amplifier Open-loop Frequency Response

I would expect the gain-bandwidth product to be a constant, but it's worth comparing the two on the bench before designing it in (I suggest measuring both the gain-of-10 -3dB point and the gain-of-0.1 -3dB point to have a point of comparison with the datasheet limits).

Note that the slew rate is typically a fairly good 5V/us, but you'll run into that at high amplitudes.

The terminology is a bit confusing - but you must distinguish between "open-loop gain Aol" (gain of the opamp without feedback factor B) and "loop gain (Aol*B)" (gain of the complete loop). Thus, if an opamp with feedback oscillates, you can assume that at the oscillating frequency the loop gain (AolB) is unity. More than that, it is correct that at this frequency the loop gain magnitude roll-off will be app. -40dB/dec (phase shift -180 deg). However, at which point of such an asymptotic line you will find the pole frequency? This is possible only if you know the first (lowest) pole frequency

Therefore, the best method for identifying the second pole is to record the magnitude function vs. frequency.