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

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)

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) // 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) // Bandwidth seems to be missing ???