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amplifier stability and compensation

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

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  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
  2. Mark

    Mark Guest


  3. Jim Thompson

    Jim Thompson Guest

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

    ...Jim Thompson
  4. Don Pearce

    Don Pearce Guest

    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
  5. Joel Kolstad

    Joel Kolstad Guest

    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 :) ).

  6. I read in that Joel Kolstad
    That'll be the day!
  7. 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

    Or don't trust me - observe reality for awhile - it's kinda fun, sometimes. ;-)
  8. Boy, ya got us there! A negative resistance device will oscillate ALL ON
    ITS OWN, given a suitable resonance in the neighborhood. %-}
    "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 Bear

    Pooh Bear Guest

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

  10. John Perry

    John Perry Guest

    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?

  11. Pooh Bear

    Pooh Bear Guest

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

  12. Don Pearce

    Don Pearce Guest

    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
  13. I read in 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 Pearce

    Don Pearce Guest

    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
  15. I read in 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.
  16. Pig Bladder

    Pig Bladder Guest

    Those who can, do. Those who can't do, teach. Those who can't even teach,
  17. Pig Bladder

    Pig Bladder Guest

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

    Rich Grise Guest

    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!
  20. Jim Thompson

    Jim Thompson Guest

    You are most welcome !-)

    ...Jim Thompson
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