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LMX2572EVM: Complicated Spurs (Walking Spus)

Coney
Prodigy 80 points
Part Number: LMX2572EVM
Other Parts Discussed in Thread: LMX2572

Hello,

   I'm using the LMX2572 to sweep frequency from 30MHz to 6.4G and the frequency space  is  not fixed.  But the spurs is complicated and hard to remove.Walking Spurs is forbidden in my appliation.

  There is the .tcs File with TICS PRO. I hope you can provide any way to remove the spurs.

  Thanks in advance.

  LMX2572_Spurs.rar

  • 0
    TI__Expert 5370 points
    Dear Coney,

    I openned your tcs files. There are two of them showing 0.01 Hz away from 1/5 fraction and 0.4 Hz from 4/5 fraction. I have not tried this on the EVM so I am not sure of the walking spur you are reffering to. Your frequency resolution is very high. Do you really need to be 10 mHz away from 1/5 fraction? this is very close to minimum resolution of the DS for 100 MHz PFD.

    If you can reduce your frequency resolution, you may be able to get better results by also changing your FPD frequency with the MULT/divider on the reference path. For example you could consider 75 MHz PFD by doing 100/4*3. You may also look at the modulator order but I can see you already had 2nd and 3rd order for your two examples.

    Regards, Simon.
  • 0 in reply to Simon Damphousse
    Prodigy 80 points
    Dear Simon,
    Thank you for your advice and it did work well.
    In my design, the LMX2572 need generate any frequency so the frequency resolution is important.
    I hope to know in which condition the walking spurs would appear and the resson.

    Best Regards,Coney.