How to sim the phase noise of VCO with /2 circuit???

[gggould]

Hi all,

I am designing a 2GHz VCO with /2 circuit.
Now I can use spectre to simulate the phase noise at 2GHz VCO output.
But can anyone tell me what is the correct setting to simulate the phase noise at the /2 circuit, which should be 1GHz ???
How about if I replace the /2 circuit with a *2 circuit??

Thanks very much,

gggould

 

[hanm]

Is there any difficulties?

 

[VSWR]

Theoretically the SSB phase noise level will DECREASE by 20*logN through a frequency divider. In your case the phase noise performance of your 2 GHz VCO will DECREASE by 20*log2 = 6 dB. But only down to the noise floor level of the /2 device itself. Usually at -140 dBc/Hz or so, consult the data sheet of your /2 divider.

If you instead put a frequency doubler after your VCO, the SSB phase noise level will INCREASE by 20*log2 = 6 dB.

It's very important to understand these mechanisms BEFORE putting it all into the computer...