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LMX2594EVM: many spurs beyond frequency sweep range

Part Number: LMX2594EVM

Dear,

 One customer used LMX 2594EVM for frequency sweep, the bandwidth is 200Mhz, sweep range is 7.6G ~7.8Ghz, but there are many spurs less then 7.6Ghz and more than 7.8GHz. What is the reason? 

The last image is the frequency which has been divider by 6,  while the above two images are not divider, sweep time is 100ms.

 The frequency point is no problem, and the PLL lock indication has all right, when the sweep frequency mode, the PLL lock LED is darkness. I am not sure if it hasn't lock when frequency sweep.

Best regards

Kailyn 

  • Hi Kailyn,

    couple of issues:

    1. fpd = fosc, you don't need to x2 and then R=2

    2. 5MHz threshold is too small. Suggest make it 50MHz

    3. min. VCO calibration time is too small. suggest make it at least 30µs.

    4. RST in Ramp0 should be  = 0.