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Phase noise in vco, mixer and amplifier

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drcham

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Hello! I've plotted VCO spectrum in rad^2/Hz. Now i have to apply amplifier noise and mixer noise. I have NF(db) and Gain(dBm) from datasheets. How can i apply it ? Can just summarize as VCO+ampNF-Gain etc. ?
I am really lost with all these parametrs... any help will be very appreciated.
 

You have to apply the Friis formula for noise to calculate the overall noise figure of your system (amplifier + mixer + everithing else). Once you have calculated it just sum VCO phase noise + total noise figure.

If first stage (closer to VCO): noise figure = NF1, Gain = G1
second stage: noise figure = NF2, Gain = G2
third stage: noise figure = NF3, Gain = G3

FRIIS --> total noise figure = NF1 + (NF2 - 1)/G1 + (NF3 - 1)/(G1*G2) .. and so on. both NF and Gain have to be, here, in linear units and not in dB

Gain is the power gain and not the voltage gain.
 
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    drcham

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lets take this system as example.
100_1289377933.jpg

albbg Thanks. i've read about FRIIS formula in the wiki. It is just what i need.
Now, when i have overall noise figure for all units after VCO. How can i apply it VCO phase noise ? I can't find VCO NF in the datasheet.
 

drcham said:
lets take this system as example.
100_1289377933.jpg

albbg Thanks. i've read about FRIIS formula in the wiki. It is just what i need.
Now, when i have overall noise figure for all units after VCO. How can i apply it VCO phase noise ? I can't find VCO NF in the datasheet.
Click to expand...

Vco is one port device; NF is for two port components. So it does not apply.

---------- Post added at 16:19 ---------- Previous post was at 16:02 ----------

NF=(s/n)in-(s/n)out, all in dB. So s/n at output=(s/n)in-NF,
PN=noise-signal, dBc/hz
So you can figure it out, PN out=PN in+NF
 
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cmm I thought that NF=SNRi/SNRo So SNRo=SNRi/NF
Well.. my mistake. it is noise factor.
 
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