The circuit is in itself quite unstable. The key is getting just the right response taking into account the speed, position, and inertia of the object versus the strength and time lag of the coil. They describe Bode plots there. What I'm getting at is that a DSP microcontroller can do a bangup job of this, better than analog, IF you know what you're doing. A non-DSP chip may not be able to do calculations fast enough to keep it stable. Well, it's not a real fast device so it may be possible... who knows.