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chopper amplifier, feedback feasible?

Discussion in 'Electronic Design' started by Roger Bourne, Apr 5, 2007.

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  1. Roger Bourne

    Roger Bourne Guest

    Hello all,

    I want to implement a chopper amplifier (differential input, single
    output) into a follower topology. Since a chopper amplifier works by
    square wave modulating the input (chopping, originally by a mechanical
    switch), amplifying the resultant AC signal,
    and then synchronously detecting the amplified signal.... (copied this
    bit from another post), is a follower topology (minus input shorted
    with output) feasible with a chopper amplifier, or will the feedback
    destroy basic chopper amplifier principle?

    In other words, can a chopper amplifier be operated only in "open-
    loop" mode (no feedback), or can the chopper amplifier replace op-amps
    in typical op-amp topologies, meaning that it can handle feedback.

    I am using the chopper amplifier to remove a signal's flicker noise.
    This is why I am employing the chopper amplifier in a follower
    topology.

    Any help will be appreciated.


    Regards,
    -Roger
     
  2. I'm not sure if you have got the concept straight. Besides, I can't see how
    any kind of amplifier can help you "remove" any kind of noise from a signal.
    If all you want is an amp with very low 1/f noise, maybe a chopper
    stabilized opamp is what you need.

    robert
     
  3. Roger Bourne

    Roger Bourne Guest


    I just read some more on chopper amps (....prompted by your
    comment :)). I get it now, chopper amps remove/attenuate the 1/f
    noise contribution of the amp only. Hmmm..... I guess I will have to
    find a way to introduce the the chopper amp in the feedback loop that
    is responsible for producing the very-noisy 1/f signal. That should
    not be too difficult (i hope) since the noisy signal stems from an op-
    amp in follower configuration. That brings me back to my original
    question, can chopper amps function with feedback ?


    -Roger
     
  4. On 5 Apr 2007 08:04:31 -0700,
    Without knowing any more about the kind of signal being processed, this
    brings me back to my original suggestion: Read up on chopper-stabilized
    opamps (very different from chopper amps which have gone out of fashion
    decades ago). Possibly you can just replace your noisy opamp follower
    by dropping in a chopper stabilized one and be done.

    When doing research on this, you can also look for "zero drift" opamps
    which is another name for the same thing. LT have a few cute app notes
    on their site (www.linear.com).

    robert
     
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