Help: How to Derive noise (Step) factor

Thread Starter

wjlim

Joined Apr 4, 2013
1


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.. :)
 

YokoTsuno

Joined Jan 1, 2013
43
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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