On Mon, 11 Jan 2010 19:51:04 -0000, "David Looser"
wrote:

"Don Pearce" wrote in message
...
On Mon, 11 Jan 2010 18:19:50 -0000, "David Looser"
wrote:


It may have been "unheard of", but it existed all the same. Any amplifier,
with or without feedback, can exhibit slew-rate limiting if the bandwidth
is
insufficient to cope with the rate of rise or fall of the input signal.

Excessive bandwidth is the cause of the problem.

You mean excessive bandwith of the input signal I presume. That's another
way of saying insufficient bandwidth in the amplifier.


Excessive bandwidth of the signal reaching the dominant pole in the
amplifier - that is cured by reducing the bandwidth of the amplifier
prior to that point. A single pole exactly counters the rising current
that causes slew rate limiting. You cannot dictate the properties of
the incoming signal - you must make sure that the amplifier has a
bandwidth that does not exceed the maximum slew rate.

Slew rate limiting is
in fact plain ordinary limiting (sawing the tops off a sine wave) but
in the current domain when feeding a capacitor. Because of the
differentiation it looks in the voltage domain like a straight slop.

That's one mechanism, there are others, the Miller effect for example.


The Miller effect is exactly what the dominant pole does - just at a
different scale. Charging current in the Miller capacitance is what
gets limited.

Excessive bandwidth permits large fast signals that will show limiting
of this kind.

Indeed, excessive bandwidth of the incoming signal. But as Jim showed a
simple passive filter on the input to the amplifier solves it.

Reducing the bandwidth of the amplifier.

d