← RF Engineering Tools

Tool 03

System Noise Figure

Analyze cascaded gain, noise factor, equivalent noise temperature, and total receiver noise figure across RF chain stages.

Parameters

Add each RF chain stage in signal order, then enter its gain and noise figure in dB. Place lossy parts and active devices where they actually appear in the receiver chain.

StageGain [dB]NF [dB]Order

Stage Results

Stage 1

LNA

Cum. NF 1.000 dB
Gain
20.000 dB
NF
1.000 dB
Cumulative Gain
20.000 dB
Noise contrib.
1.000 dB

Stage 2

Mixer

Cum. NF 1.179 dB
Gain
-6.000 dB
NF
8.000 dB
Cumulative Gain
14.000 dB
Noise contrib.
-12.749 dB

Stage 3

IF Amp

Cum. NF 1.455 dB
Gain
30.000 dB
NF
5.000 dB
Cumulative Gain
44.000 dB
Noise contrib.
-10.651 dB

Formulas

Total Noise Factor

The Friis cascade equation sums each stage noise contribution divided by the preceding gain.

Ftotal=F1+F2−1G1+F3−1G1G2+⋯+Fn−1∏i=1n−1GiF_{total} = F_1 + \frac{F_2 - 1}{G_1} + \frac{F_3 - 1}{G_1G_2} + \cdots + \frac{F_n - 1}{\prod_{i=1}^{n-1}G_i}

Noise Figure dB Conversion

Convert the linear noise factor to noise figure in dB.

NFdB=10log⁡10(Ftotal)NF_{dB} = 10\log_{10}(F_{total})

Total Gain

Sum the dB gain of each stage to calculate total gain.

Gtotal,dB=∑i=1nGi,dBG_{total,dB} = \sum_{i=1}^{n}G_{i,dB}

Calculations are performed with linear noise factor and linear gain, then displayed in dB.