amplifier stability and compensation

pspice?

Mark

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

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

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

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.

Pearce Consulting

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. ;-)

I read in sci.electronics.design that Joel Kolstad wrote (in ) about 'amplifier stability and compensation', on Fri, 6 May 2005:

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

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

Likewise. Even worse it's clear he has no real world experience. That's typical academia for you.

Graham

True.

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

Graham

That isn't tricky at all. The signal builds until the amplifier hits the rails and there is no more gain.

I don't agree. There is nothing intuitively bad about positive 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.

Pearce Consulting

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

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

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.

Pearce Consulting

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)

I read in sci.electronics.design that Don Pearce wrote (in ) about 'amplifier stability and compensation', on Sat, 7 May 2005:

It MAY limit on output voltage but in general the limiting can be due to any one of several possible non-linearities.

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

I read in sci.electronics.design that Don Pearce wrote (in ) about 'amplifier stability and compensation', on Sat, 7 May 2005:

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.

You are most welcome !-)

...Jim Thompson

That's great rich, I'm fairly ok with the lesson plan, but i'm short on practical aids and examples. I could just scrible up a few circuits on pspice but i'd love to get a look at how other people have attempted it and then take what i like about their views, and ideas of my own, and meet somewhere in the middle.

For the lesson i'm going to stick to a simple style; Introduce Explain Demonstrate Get the students to imitate Get the students to practice

Would anybody do anything differently?