common collector colpitts oscillator?

Discussion in 'General Electronics Chat' started by newman123, Jan 9, 2007.

  1. newman123

    Thread Starter New Member

    Nov 23, 2006
    4
    0
    Hi everyone. I have some questions about the CC colpitts oscillator.
    Most books say the CC oscillator is very rare to use, and the cc
    configuration is usually used for impeadance matching(high in- low out)
    or buffer amplifier.But I find that some uhf PNP transistor is designed for CC oscillator.(and the datasheet emphasizes the the term "for common collector")
    What is the purpose to use common collector configuration rather the
    common emitter configuration?
    Anyone knows the basic diagram for CC colpitts oscillator?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Common collector transistors have gains of less than unity. Oscillators have to have gains graeter than unity in order to oscillate. So a common collector colpitts oscillator seems more trouble than it is worth.

    Got a number for that UHF PNP transistor?
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
  4. bartona

    New Member

    Jun 29, 2010
    1
    0
    Microchip has a very good application note on oscillators: AN826
    Crystal Oscillator Basics and Crystal Selection​
    for rfPIC
    TM and PICmicro
    ® Devices
     
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