Chip ID

[Haible Juergen]

	>>...but does NOT exhibit the dreaded "phase reversal" when the
	>common mode input range is exceeded (when the input is
overdriven)....
	>
	>But it does oscillate at high frequency when the input voltage gets
near
	>one of the rails if you use it as a voltage follower. Never seen
that
	>before!

I didn't follow the thread, so I don't know about which chip you're writing.

I found a similar thing on a "high end audio type" opamp from AD. (forgot
the
part number). Could hardly believe it. As long as you did not overdrive it,
all's fine. But when you drive it almost to the rails, it starts
oscillating,
and it sounds *awful*. 
This behaviour has its benefits, however, when you're building OTA filters
with an opamp buffer in noninverting configuration. These tend to latch up
on heavy overdrive (negative feedback becoming positive feedback, the
filter cap making sure it cannot be thrown out of the latchup with an input
signal ...), and the oscillation prevent this.
Now I wonder why it is so increadibly hard to build JFET input opamps that
have a decent overdrive behaviour. There are only a few that have no
phase reversal - I wonder if these all work with oscillation instead, or
if there are really "tame" ones ?

JH.