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VCO phase noise three questions

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mouzid

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VCO phase noise

Please pardon my ignorance.

I have three questions:

1- When we say that a VCO is better for the same frequency offset ?
Consider a VCO whith a phase noise of -85.5 dBc/Hz @10KHz and the second having a phase noise of -100.2 dBc @10KHz Which is better

2- When we say that a VCO is better for same the phase noise ?
Consider VCO1 phase noise is -85 dBc @1KHz and VCO2 -85dBc @1Mhz.
Which one is better.

3- The joined figure is a phase noise plot of a VCO (2.5Ghz-4.5Ghz)
the figure shows a phase noise of -63 dBc/Hz@1 Mhz offset. Is it a good VCO ?
 

Re: VCO phase noise

Is my question too stupid or too difficult for you ?
 

Re: VCO phase noise

Hi mouzid,

1/ dBc is the noise gain compared to the frequency carryier
I hope some friends give you more detail coz i'm not an expert in that field.
 

    M

    mouzid

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Re: VCO phase noise

1. Obviously the lower the phase noise the better it is. -100dBc/Hz is better.
2. Close-in phase noise will be high due to contributions from the flicker noise and up-converted flicker and thermal noise. So -85dBc/Hz at 1KHz is better. -85dBc/Hz at 1MHz will have higher noise at 1KHz.
3. It depends on your application and the amount of power you spend in the VCO.
 

    M

    mouzid

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VCO phase noise

It seems that your VCO is a ring oscillator, not a LC-VCO. I would say the phase noise is abit bad, unless you burn very little power.
 

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