I have an OPA690 that works fine during normal operation, but weird things happen when it saturates.
After hitting the negative power rail (-5V), the amplifier produces a damped sine response (sine * negative exponential). It is a very small signal (mV) that takes lots of averaging to be able to see. It also takes a very long time to fade (milliseconds). The amplifier is setup to have a bandwidth of a few hundred MHz, so it is surprising to see something last milliseconds.
I can't provide much more information. I am just wondering if anyone has heard of something like this before.
I will delete this question if it is too vague and I do not get any responses.