VCO: Eliminating spurs in the psd plot

[AdvaRes]

Hi all,

1- The psd plot of a VCO output (simulated) shows two kinds of spurs.
Spurs appears:
Aroud the carrier frequency fc
At the frequency 2fc, 3fc ...etc

What are the causes of these spurs and How to eliminate each kind ?

2- The carrier frequency of the VCO is 4G the figure bellow shows the obtained psd and the wanted psd plot.
Actually another simulation showed that when fc=4.3G the spurs appears only at 2fc, 3fc etc...
Do you know why ?
All your comments are welcomed !

Thanks in advance.

 

[saro_k_82]

I hope the transient looks like sine and not so distorted as seen in this plot. Can you show your transient and the way you get your psd plot.