Calculadora de Figura de Ruído em Cascata
Calcule a figura de ruído total de estágios em cascata usando a fórmula de Friis.
Total Noise Figure
1.62 dB
Total Noise Figure vs Stage 1 Noise Figure
Formula
## Friis Noise Formula for Cascaded Stages The overall noise figure of a chain is dominated by the first stage, especially if it has high gain. ### Formula **F_total = F_1 + (F_2 - 1)/G_1 + (F_3 - 1)/(G_1 x G_2)** All values in linear (not dB). Convert: F = 10^(NF_dB/10), G = 10^(Gain_dB/10). **NF_total(dB) = 10 x log10(F_total)** This is why low-noise amplifiers (LNAs) are placed at the front of receiver chains.
Exemplo Resolvido
Three-stage receiver: LNA (1.5 dB NF, 20 dB gain), mixer (6 dB NF, 10 dB gain), IF amp (10 dB NF).
- 01F1 = 10^(1.5/10) = 1.413, G1 = 10^(20/10) = 100
- 02F2 = 10^(6/10) = 3.981, G2 = 10^(10/10) = 10
- 03F3 = 10^(10/10) = 10
- 04F_total = 1.413 + (3.981-1)/100 + (10-1)/(100 x 10) = 1.413 + 0.030 + 0.009 = 1.452
- 05NF_total = 10 x log10(1.452) = 1.62 dB
Perguntas Frequentes
Why does the first stage matter most?
The noise contributions of later stages are divided by the gain of all preceding stages. High first-stage gain makes later stages negligible.
What is a good noise figure for an LNA?
For sensitive receivers, LNA noise figures below 1 dB are common. Consumer Wi-Fi receivers may have 3-5 dB.
What is noise temperature?
An equivalent way to express noise. T_eq = 290 x (F - 1) Kelvin, where F is the linear noise factor.
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