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What exactly is "adaptive biasing" for amplifiers

Discussion in 'Electronic Design' started by [email protected], Nov 19, 2012.

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  1. Guest

    Could some electronics guru shed some light
    on this ? What exactly is "adaptive biasing"
    in respect to power amplifiers ? How exactly
    does the "adaptive" term come in, that is
    adapt to changes in which parameter -- input
    signal amplitude maybe ? Any hints, suggestions
    would be helpful. Thanks in advance.
     
  2. Bill Sloman

    Bill Sloman Guest

    Beats me. In audio amplifiers, the output transistors get hotter if
    you play a lot of loud music, and if the class A/B biassing hasn't
    been set up right, the bias current flowing through the output
    transistors at zero signal can get quite a lot bigger than it is when
    the transistors are cold.
     
  3. Guest

    It's just a general term to describe a variable power amplifier bias that is input signal level dependent. It can run the gamut from audio to RF, in applications where 1) relatively large signal dynamic range must be accommodated and 2) there is some necessity to conserve amplifier loading of the DCsupplies and/or 3) adaptive biasing is required to meet linearity performance.
    No expert here, just what I surmise from a quick look at the Google search abstracts.
     
  4. miso

    miso Guest

    In the audio range, adaptive biasing is such that the Iq is very low
    unless you need the power. There are some tricks such as when a slew
    situation is detected you juice the long tail pair to attempt to recover
    faster.

    Eric Vittoz from Swiss Federal has papers and a book or two of such tricks.
     
  5. Mark

    Mark Guest


    If one of the requirements is to conserve power, why would you use a
    Class A output stage in the first place?

    Mark
     
  6. Grant

    Grant Guest

    700uA standby current is hardly low power either, but how else do you make
    an amplifier for 1V operation, if not class A?

    Not a lot of wiggle room there.

    Grant.
     
  7. miso

    miso Guest

    I think when you reach the point where a hearing aid is required,
    harmonic distortion isn't much of an issue due to reduced bandwidth. ;-)
     
  8. miso

    miso Guest

    Fortunately I know nothing about hearing aids.
     
  9. Bill Sloman

    Bill Sloman Guest

    Nanoprocessors would be quite small enough. The diameter of most atoms
    is between 200 and 400 picometres, so building a picoprocessor would
    be tricky.
     
  10. josephkk

    josephkk Guest

    At the era of the design, probably not much choice; use class D today.

    ?-)
     
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