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AD9375 DAC Output spur

Category: Software

I am using AD9375 interfaced with Xilinx Mpsoc +XCZU11EG. 

In DAC output, (DDS and NCO)I getting spurs around my Output frequency ( where delta is around 25kHz and 50kHz) which is degrading my SFDR . RBW - 100Hz, 

My sampling rate is 245.76MSPS and device  clock is 122.88MHz and single shot  SYSREF -> 0.96MHz

I have checked my clock output, i got exact frequency what i need which is attached below without spurs.

Then i checked all my Regulators OUTPUT.  In 25KHz , i am getting around -80dBm. (too Less)

 Kindly let me know why this is 25kHz ( Delta Tone) is there near to the output frequency

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  • even if i change my tone close to LO(1MHz, 5Mhz) or far away (around 40Mhz), I am seeing the similar spur

    Are the spurs also shifting accordingly, i.e, when the tone is shifted by 5MHz, the spurs are also shifted by 5MHz? Or the spurs are still at 25KHz offset from LO?

    Can you try with external LO?  Also, check the power supply of your custom board. Make sure that is clean and jitter free. 

  • That 25kHz is close to my LO+MSG not to my LO. If i change my LO 

    Like LO = 4500MHz and Message = 10MHz . I can observe the spur at (4510Mhz -25kHz) and (4510+25kHz). 

    LO=4600MHz and Message = 10MHz. I can observe the spur at (4610-25kHz) and (4610-25kHz)

    I don't have any choice to provide external LO.

    Even i have checked ADRV9371 EVM, from 0to 100kHz, Noise floor is around -80dBm.

    Few rails have maximum peak.

    Same, Noise floor we are acheiving in Custom Board. But we have peaks at 25kHz and 50kHz(Less than -80dBm). Thats the only limit

    Could you let me know the API function for configuring LOOP filters of Synthesizers of RX, TX and ORX

  • Even if i reduce the tone, spurs are reducing but little (around 1dB). not more than that.

    How much power was reduced in dBFS?. Can you reduce by -6dBFS and check.

    You can use the API setRfPllLoopFilter(),  to set the PLL loop bandwidth.