amplifier stability and compensation

Discussion in 'Electronic Design' started by [email protected], May 5, 2005.

1. Guest

Hi guys, I've a project on amplifier stability and compensation. I'm
about half way through it now, anyboody got any info or anything
interesting. It's a fairly simple project, what i have to do is complie

notes that will be used to teach 3rd year electronics students about
amplifier stability.

The next stage is where i create four one-hour lab session to
demonstrate how to;

calculate the loop-gain,
show how the loop gain varies with frequency,
show how a amplifier becomes unstable,
demonstrate how to stabilise it.

I haven't completely decided on these labs so if anybody thinks they'd
do it differently please let me know.

I've already decided that i'm going to use simple op-amp circuits in
these labs. What i need to do is create these circuits. Does anyboddy
have any examples / suggestions/ ideas on what circuits would suit the
labs?

pspice?

Mark

3. Jim ThompsonGuest

I would have responded, but "dr_stephen_quinn" is clueless... trying
to "teach" material he knows nothing about :-(

...Jim Thompson

4. Don PearceGuest

One thing I would suggest is that you start with an oscillator - how
it works, and what conditions you need to achieve to ensure
oscillation. That way, when you move on to amplifier stability, your
students will understand what you are trying to avoid, and why.

d

Pearce Consulting
http://www.pearce.uk.com

The tricky part is always, "But if the loop gain starts out as being greater
than one, what causes it to drop to one once oscillations build? And how much
bigger than one should it be anyway?" If you are going to go this route, I'd
probably be tempted to use HP's old audio oscillator that uses the light bulb
as the negative resistance device!
I think it's intuitively clear to most students that "bad things happen" just
from looking at the math when you hit zero phase or gain margin, even if it
may not end up being an oscillator (and there times when a badly compensated
op-amp just swings to a rail and sits there rather than oscillating ).

---Joel

6. John WoodgateGuest

^^^^^^^^^^
That'll be the day!

7. Rich The Newsgroup WackoGuest

Trust me - there ain't nothing intuitive about it, when you're working
with equations. Unless you're talking about the "intuition" that says,
"That's an asymptote" or "that's a cusp" or that sort of thing.

And trust me, arithmetic students don't have the experience with real
world components for any of their behavior or attitudes to be called
"intuitive".

Or don't trust me - observe reality for awhile - it's kinda fun, sometimes. ;-)

8. Rich The Newsgroup WackoGuest

Boy, ya got us there! A negative resistance device will oscillate ALL ON
ITS OWN, given a suitable resonance in the neighborhood. %-}
--
Cheers!
Rich
------
"There was a young man of Calcutta,
Who tried to write "****" on a shutter.
When he got to c-u,
A pious Hindoo
Knocked him ass-over-head in the gutter."

9. Pooh BearGuest

Likewise. Even worse it's clear he has no real world experience. That's

Graham

10. John PerryGuest

On the other hand, he's actually asking us for guidance. How many
academics do you know whose noses aren't too high in the air to notice
us who've burnt our fingers with soldering irons?

jp

11. Pooh BearGuest

I have absolutely NO idea how the ones on my degree course ever got to teach
*anything*.

Graham

12. Don PearceGuest

That isn't tricky at all. The signal builds until the amplifier hits
the rails and there is no more gain.
feedback - indeed the term is used in the media these days to mean a
good thing. That stuff gets ingrained at a cultural level and can be
hard to shift.

d

Pearce Consulting
http://www.pearce.uk.com

13. John WoodgateGuest

I read in sci.electronics.design that Don Pearce <>
It MAY limit on output voltage but in general the limiting can be due to
any one of several possible non-linearities.

14. Don PearceGuest

Not in an amplifier it isn't. One hopes that there are no other
non-linearities short of limiting. In an RF oscillator, of course, the
limiting action tends to be rather softer.

d

Pearce Consulting
http://www.pearce.uk.com

15. John WoodgateGuest

I read in sci.electronics.design that Don Pearce <>
There are well-designed amplifiers and simple one- or two-transistor
amplifier 'designed' by students. Limiting on base-emitter non-linearity
or one-sided limiting at the collector are common phenomena.

Those who can, do. Those who can't do, teach. Those who can't even teach,

And, of course, when reality hits the rails, nobody knows how to deal with
it.

18. Guest

Ok, to clarify;
I know the amplifier stability criterion, all i'd like to see is
what labs you think would be useful in teaching the subject.
The project concerns the METHOD of instruction of this topic, so
any links to university sites or completed projects would be spiffing.

Thanks to those who had a positive input.
(F.Y.I. that's not you Jim)

19. Rich GriseGuest

Method of instruction? Ask leading questions, and let them use all of
the references they can carry.

Start at the beginning, and answer ALL questions - encourage interruptions.

Tell them what you intend to accomplish in the session, and let them
participate in achieving that goal.

Other than that, I don't really know how to teach. Be firm, but fair
and consistent.

Yeah, that pretty much sums it up from my perspective.

Break a Leg!
Rich

20. Jim ThompsonGuest

You are most welcome !-)

...Jim Thompson