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edited May 16, 2013 at 21:52

Assuming that the problem is the capacitive load (gate of the MOSFET) some ideas are:

In audio amplifiers, the classic approach for defending against capacitive loads is the inclusion of an output inductor, often in series with a resistor. Just an idea to keep in mind: don't forget inductors as a way of isolating from capacitances.
Ever notice how the data sheets of linear voltage regulators always recommend a bypass capacitor on the output? This helps with a capacitive load. While it seems like a paradox, the reasoning is that the deliberately planted capacitor has a higher capacitance which swamps the small capacitance of the load, thereby creating a dominant pole at a lower frequency. Try a capacitor from the output of the op-amp to ground, of 0.1uF to 1uF.
Since you're using the + input for negative feedback, there is a big opportunity in this circuit to add Miller compensation in the form of a more local negative feedback loop: a capacitor connected from the op-amp's output to the - input, instead of to ground.

Your output stage is common-source, and so it has gain! The op-amp already has gobs of open-loop gain, and you're adding more into the loop. Consider an output stage that doesn't add any more gain: see Andy Aka's answer.

Assuming that the problem is the capacitive load (gate of the MOSFET) some ideas are:

In audio amplifiers, the classic approach for defending against capacitive loads is the inclusion of an output inductor, often in series with a resistor. Just an idea to keep in mind: don't forget inductors as a way of isolating from capacitances.
Ever notice how the data sheets of linear voltage regulators always recommend a bypass capacitor on the output? This helps with a capacitive load. While it seems like a paradox, the reasoning is that the deliberately planted capacitor has a higher capacitance which swamps the small capacitance of the load, thereby creating a dominant pole at a lower frequency. Try a capacitor from the output of the op-amp to ground, of 0.1uF to 1uF.

Assuming that the problem is the capacitive load (gate of the MOSFET) some ideas are:

In audio amplifiers, the classic approach for defending against capacitive loads is the inclusion of an output inductor, often in series with a resistor. Just an idea to keep in mind: don't forget inductors as a way of isolating from capacitances.
Ever notice how the data sheets of linear voltage regulators always recommend a bypass capacitor on the output? This helps with a capacitive load. While it seems like a paradox, the reasoning is that the deliberately planted capacitor has a higher capacitance which swamps the small capacitance of the load, thereby creating a dominant pole at a lower frequency. Try a capacitor from the output of the op-amp to ground, of 0.1uF to 1uF.
Since you're using the + input for negative feedback, there is a big opportunity in this circuit to add Miller compensation in the form of a more local negative feedback loop: a capacitor connected from the op-amp's output to the - input, instead of to ground.

Your output stage is common-source, and so it has gain! The op-amp already has gobs of open-loop gain, and you're adding more into the loop. Consider an output stage that doesn't add any more gain: see Andy Aka's answer.

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created May 16, 2013 at 20:37

Assuming that the problem is the capacitive load (gate of the MOSFET) some ideas are:

In audio amplifiers, the classic approach for defending against capacitive loads is the inclusion of an output inductor, often in series with a resistor. Just an idea to keep in mind: don't forget inductors as a way of isolating from capacitances.
Ever notice how the data sheets of linear voltage regulators always recommend a bypass capacitor on the output? This helps with a capacitive load. While it seems like a paradox, the reasoning is that the deliberately planted capacitor has a higher capacitance which swamps the small capacitance of the load, thereby creating a dominant pole at a lower frequency. Try a capacitor from the output of the op-amp to ground, of 0.1uF to 1uF.