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Questions for common emitter, collector and base amplifier.

  1. Aug 28, 2015 #1

    goodphy

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    Gold Member

    Hello.

    I'm now studying transistor amplifier circuit and I have some confusion of definition of amplifier classification.

    I thought common emitter means emitter side is grounded, although there is actually some elements between emitter and ground in practice. So I thought "common" means "grounded".

    But when I looked at other configuration like common collector (See http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/npncc.html#c1) it seems collector side is not grounded side.

    How is each configuration defined? How does each configuration differ from the other?
     
  2. jcsd
  3. Aug 28, 2015 #2

    meBigGuy

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    The collector is grounded in the link you provided.

    There is an input node, and output node, and "the other node" which is considered common to both input and output.
     
  4. Aug 28, 2015 #3

    LvW

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    Goodphy - the term "grounded" means: Common reference point for input, output as well as DC supply.
    And in most cases, this ref. point is called "ground".
    More than that, you must know that the three basic configurations require only "signal ground".
    For exampole, in the the common collector configuration the collector node is "grounded" - as far as signals are concerend (zero internal resistance of the DC supply).
    There may be one exception: In common emitter configuration we very often see a resistor RE between the emitter node and ground.
    It is the purpose of RE to fix and stabilize the DC operational point. If this resistor is shorted by a capacitor we again of "signal ground" at the emitter node (classical common-emitter configuration) - however, sometimes it is not bypassed. Then, we have "common emitter with signal feedback".
     
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