I'm trying to obtain an op-amp's open loop DC transfer characteristic curve on an oscilloscope, and from the curve, the open loop gain.
Here is an image (from some random website) showing the curve I wish to obtain:
My attempt at attaining the curve was: tie one of the inputs to ground and the other to the function generator, then get the function generator to put out a ramp function (representing my DC sweep). I then looked at the output of the op-amp with the scope and zoomed in and was able to see an image similar to the image I in the above link. I then tried putting the scope into x-y mode (and though that worked, the result was pretty low quality), so I gave up on the x-y idea. I then tried to calculate the open loop gain (would should be around 100dB = 100kV/V) by shifting the two curves on the scope so they both equaled 0V at the same time, I then got a point from the output of the op-amp and the corresponding point from the ramp function and found the gain to be way out… It was around 800… So my two issues are, the open loop gain is way off and the whole approach seems so inaccurate. I can even zoom in much on the curve because I don't really have anything to trigger off.
Does anyone have any suggestions as to perhaps what I've done wrong, or a better way to the transfer characteristic of the op-amp on the scope?
If there is no accurate way, does anyone have any idea of how I could just obtain the open loop gain of the op-amp? Since it's open loop gain is roughly 100dB, it means that I need to generate like 1uV on one of its inputs just to get 100mV output…