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Load-pull limitations in PA design?

Discussion in 'Electronic Basics' started by billcalley, May 17, 2007.

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  1. billcalley

    billcalley Guest

    Hi All,

    I will be tasked with finding the proper Zin and Zout for a 1W RF
    power transistor's maximum Pout, gain, and PAE on a Maury load-pull
    station, but something has just occurred to me: won't any results
    coming from such a PA load-pull tuning method be relatively
    inaccurate? The reason why I say this is that the final (non-linear)
    PA circuit, when eventually placed in the RF transmitter itself, will
    be seeing a bandpass filter and/or an antenna, both of which mean that
    the PA will no longer be seeing the very wideband 50 ohm termination
    it saw in the load-pull tuning station. This means that the non-
    linear's PA harmonics will be strongly reflecting back off of the
    filter's and/or antenna's stopbands and back into the PA's output,
    affecting its PAE, stability, gain, etc. Aren't I correct about
    this? And if so, how do I address this problem??

    Thanks for any help!

  2. In ANY design, the nicely manicured specs, achieved on bench should be
    derated about 50% once you produce more than one unit on production line.
    Happens in all designs.
    And it is NOT a problem, this IS reality.


  3. joseph2k

    joseph2k Guest

    personally i am much opposed to using non-linear amplifiers without truly
    compelling requirements to the otherwise. efficiency is more dependant on
    circuit topology to the point that is is unreasonable to be non-linear.
  4. Joerg

    Joerg Guest

    Power amplifier are pretty much all non-linear, except for classic
    single-sideband or TV power amps. But even there tricks such as pulse
    modulation had made some inroads. However, in this age of spread
    spectrum comms and digital TV (if and when it really comes...) their
    days may be numbered.

    Just think about it: The big final power amp of an AM transmitter
    usually has an efficiency well north of 80%. That wouldn't be possible
    if this was a linear amp. These days it's basically a very fast switch
    with it's supply voltage modulated via a PWM stage.
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