Power Gain question

Discussion in 'General Electronics Chat' started by RFeng, Jul 4, 2012.

  1. RFeng

    Thread Starter New Member

    May 30, 2012
    27
    0
    Hi,

    I'd like to measure the Power Gain of the following PA.
    Am I doing it correctly in the following way?
    Please notice that I measure vin AFTER RS (not Before RS).

    Pin_avg = avg (iin * vin)
    Pout_avg = avg (iout * vout)

    Gain = 10*log(Pout_avg / Pin_avg)

    Should I measure vin before RS? (i.e. measure the voltage source's voltage).

    Thanks!

    [​IMG]
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,795
    Yes, it looks like you are doing it correctly.

    No, you do not want to measure V_in prior to R_S because the power gain is the ratio of the power delivered by the amplifier to the power consumed by it. The power being dumped in R_S by the source is being consumed by the source, not the amplifier. Besides, it is possibly a modelled output resistance and does not reflect any true power consumed at all - the true power consumed by the amplifier could be a lot different, either higher or lower. The point being, that your amplifier doesn't care about those details, because it only sees the voltage applied to its input.
     
    RFeng likes this.
  3. RFeng

    Thread Starter New Member

    May 30, 2012
    27
    0
    Hi
    I thank you very much my friend!
     
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