power of sinusoid signal

Discussion in 'General Electronics Chat' started by screen1988, Jun 20, 2013.

  1. screen1988

    Thread Starter Member

    Mar 7, 2013
    310
    3
    I am reading an article about ADC. This part is confusing.
    If the analog input is a sinusoid with amplitude Vref/2 (peak-to-peak Vref), its total power is equal to Vref/ 8.
    [​IMG]
    P = U^2/R = (Vref/2√2)^2 /R = Vref/(8R)
    Why is R omitted here? I mean that why R = 1.
     
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  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I'm assuming it's because SNR is the ratio of two powers.
    Psig=Vsig^2/R
    Pnoise=Vnoise^2/R
    Psig/Pnoise=((Vsig^2)/R)/((Vnoise^2)/R)
    Psig/Pnoise=Vsig^2/Vnoise^2

    The R cancels out, so it is irrelevant.
     
    screen1988 likes this.
  3. screen1988

    Thread Starter Member

    Mar 7, 2013
    310
    3
    Thanks, that makes sense!
    I want to ask one more question.
    SNRp means "peak signal to noise ratio". Why we need to include "p" here?
    Because this is a ratio between two signals, the ratio doesn't depend on if is peak or root mean square?
     
    Last edited: Jun 20, 2013
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