Hello, I've been lurking for a while but I have finally decided to make an account since I have a question myself. I'm quite a beginner so yeah, feel free to point out any dumb stuff. Anyway, to the point.
I'm designing a digitally controlled current source in the range of 0 to 100uA (see first attachment). Basically I use a digital potentiometer (100kohm total resistance) as a voltage divider for a reference voltage of 3.3V coming from a regulator. The OpAmp is powered by [5,-5]V voltage regulators. The jumpers are just for measuring the current when the target chip is not placed so I can connect the transistor to GND and have a path for the current. The circuit works, but when I measure the negative pin of the OpAmp with an oscilloscope I can see small oscillations at a frequency of 300kHz (or 600kHz, I can't remember exactly right now). On the other hand I don't see anything if I measure the amplifier output. Furthermore, when I use a better probe (not just the crappy coaxial) the oscillations aren't there either. I assume this might be due to the capacitance of the probe that filters them out but can't confirm.
The 3.3V reference is clean (at least at that frequency, I have some other small oscillations at 12MHz due to bad bypassing in an oscillator but thats another matter). I have also attached what I think is the relevant information from the datasheets regarding stability. So.. what's wrong here?