Ac coupled Amplifier question

Discussion in 'Homework Help' started by Panterulez, Apr 8, 2009.

  1. Panterulez

    Thread Starter New Member

    Mar 25, 2009
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    [​IMG]

    According to my notes, it is stated the CC amplifier, an emitter-follower gives low output resistance and buffers the high gain stage from the relatively load resistance. I just don't seem to understand what this exactly means ? Can anyone enlighten me
     
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,283
    326
    The load is 250 Ω. If it had been connected to the collector of the C-E amplifier (through C5), then the effective collector load resistance would have been 4700 Ω in parallel with 250 Ω, and the gain of the C-E stage would have been drastically reduced.

    The emitter follower has a low output resistance to drive the low resistance load, and a high input impedance to avoid loading the C-E stage.
     
  3. jasperthecat

    Member

    Mar 26, 2009
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    0
    You could look at the theory here

    http://www.allaboutcircuits.com/vol_3/chpt_4/index.html

    or Wikipedia to better understand the various transistor configurations of

    Common Emitter, Common Base & Common collector.

    A little cheat sheet on BJT configurations helps

    CE Zin =medium Zout =medium Gain >>1

    CC Zin = Hi Zout = Lo Gain <1

    CB Zin = Lo Zout = Medium Gain >>1

    Hope this helps
     
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