I've been trying to make a current source, and have finally gotten my hands on some LM8261's which should be an 'unlimited cap drive' op-amp. The problem is, it is still oscillating.
This is the schematic and PCB layout:
I have tried to route the ground inside the loop area, close to the 5V connection for the opamp, so I could place the bypass capacitors as close as possible. Although the bigger 10uF cap has one of its legs at the groundplane (forgot to include this cap in the schematic picture.)
This is what it looks like when I probe the gate of the MOSFET:
It's all over the place.
I tried adding a 10uF capacitor across the DUT, so from VDD to ground. This removed a lot of the wierd noise and made it look almost like a sinewave:
I've tried with and without the gate resistor R1, it didn't seem to make any difference.
What is going on? Any clues on why this just doesn't work?
Solved it! With the help from @Andyaka below, I used his solution of inserting a BJT emitter follower in between the op-amp and the MOSFET, together with an integrator and got some great results!
The simulations can be seen here:
The gain/phase bode plots I made on the PCB:
Bandwidth of approximately 350kHz! Very pleased.