Help: How to Derive noise (Step) factor

Discussion in 'Wireless & RF Design' started by wjlim, Apr 4, 2013.

  1. wjlim

    Thread Starter New Member

    Apr 4, 2013
    1
    0
    [​IMG]

    Noise factor
    F = (Pnoise(out)/gain)/Pnoise(Rg)
    F = V(inoise)*V(inoise) / (4*K*T*Rg)
    F = V(inoise)*V(inoise)/(4*K*300.15*50)


    This gain definition is only for noise analysis
    gain=V(out)/V(in0)

    how does F = (Pnoise(out)/gain)/Pnoise(Rg) tansform into F = V(inoise)*V(inoise) / (4*K*T*Rg)

    please help me. thanks.. :)
     
  2. YokoTsuno

    Member

    Jan 1, 2013
    41
    9
    No idea. To me it seems that this is flawed. The 1st equation is correct. Thereafter it appears that Pnoise(out) has been substituted by Pnoise(in)*gain. This is only the case when the amplifier does not add any noise.

    1) F = (Pnoise(out)/gain)/Pnoise(Rg)
    2) F = (Pnoise(in)*gain)/gain)/Pnoise(Rg) //:confused: Flawed substitution ???
    3) F = Pnoise(in)/Pnoise(Rg)

    - When loads are matched: P = U^2/4R
    - Thermal noise from source: Pn = k*T*BW

    4) F = Unoise*Unoise/4Rg/Pnoise(Rg)
    5) F = Unoise*Unoise/(4*Rg*k*T*BW) //:confused: Bandwidth seems to be missing ???
     
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