Phase noise in vco, mixer and amplifier

[drcham]

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.

 

[albbg]

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.

 

[drcham]

lets take this system as example.

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.

 

[cnm]

lets take this system as example.

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.

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

 

[drcham]

cmm I thought that NF=SNRi/SNRo So SNRo=SNRi/NF
Well.. my mistake. it is noise factor.