LMX2594EVM: How to remove the spur @f1=1900.067MHZ, f2=1900.2MHZ

Dear Sing,

could you please send the details of your setting. reference freq used, output divder, fraction etc. I provided you with 1900.67 setting but not 1900.067.Thank you for sending the information.

Regards, Simon.

Hi Simon,

My frequency of interest is f=1900.067MHZ.

I tried my own values. PFA values below and let me know how to remove spur in output.

Hi Sing,

In both cases, suggest use div/6 so as to use a higher VCO frequency. This will push the spurs frequencies away from the carrier. Then, use a smaller loop bandwidth to further reduce the spurs amplitude. A quick trial could be simply setting the charge pump current to, say 3mA.

Hi,

Thank you for your reply.Still I am seeing the spur in the output. Can you Please give any other solution ?

FYI please find the attache image...

Hi Noel Fung,
Could please elaborate the relationship between the divider and spurs. So that I can make use of this relationship and I will try different register combinations to achieve the spur optimized phase noise.

Hi Sing,

The spurs are mainly came from crosstalk between (1)fpd and VCO (2) fpd and Nfrac (3)OSCin and VCO (4)OSCin and fout.
We can use the Pre-R divider and MULT to change the fpd, as a result, (1) and (2) will go away.
if you can use a different OSCin frequency, for example, 48MHz. Then you won't have spurs at both of your interested frequencies f1 and f2.