spurs out in ADRF6720

my DAC spectrum looks like in DACspectrum picture,                                          
Question: Why ADRF6720 output spectrum looks like in MODspectrum picture?

    •  Analog Employees 
    on Oct 9, 2019 2:05 PM over 1 year ago

    Hello,

    It looks there are 60MHz +/- N* 8KHz spurs on DAC output and Frf +/- N*16KHz spurs on ADRF6720 output spectrum. It looks spurs on ADRF6720 output are related to spur on input(DAC output) Can you check Baseband inputs to ADR6720 and LO output of ADRF6720 on pin 33 and 34?

    - check baseband inputs(I+, I-, Q+, Q-) on ADRF6720 with a oscilloscope : make sure they should be 0.5V DC biased for ADRF6720

                                                                                          : check phase relationship (180 degree between +  and - on I and Q)

                                                                                                                                     (90 degree between I and Q)

    - check LO output (pin 33 and pin34) 

    If it is possible, it would be good to check ADRF6720 output with a clean baseband inputs.

    Thanks

    Tony

  • I checked baseband input and its responds datasheet (bias 0.5V DC, 180 degree between +  and - on I and Q , and 90 degree between I and Q channel) .
    You were wrong LO output on pin 18 and 19.
    And I checked LO output  , it looks good , spurs small.

    •  Analog Employees 
    on Oct 9, 2019 6:14 PM over 1 year ago in reply to svyatikua

    Hello,

    RFout on ADRF6720 is mixed product between LO and BB. So if LO output is  good, then you may need to focus on BB. 

    I would suggest to feed clean baseband inputs to  ADRF6720 and check how it works. And let me get your register settings with Reference Frequency, PFD Frequency, LO Frequency information.

    Thanks

    Tony

  • About clean baseband inputs I will try little later,
    but why this spectrum incorrctly transferred on 2.3 GHz /cfs-file/__key/communityserver-discussions-components-files/114/DACspectrum.jpg ?


    All registers:
    Address
    16#00#,      16#01#,     16#02#,      16#03#,      16#04#,
    16#10#,      16#20#,     16#21#,      16#22#,      16#30#,
    16#31#,      16#32#,     16#33#,      16#40#,      16#42#,
    16#43#,      16#45#,     16#49#

    Values:
    16#0000#,  16#F67F#, 16#004A#, 16#AC33#, 16#F600#
    16#F67F#,  16#0C26#, 16#000B#, 16#2A01#, 16#0000#,
    16#1101#,  16#09E2#, 16#0787#, 16#0010#, 16#000E#,
    16#0000#,  16#0000#, 16#16B0#


  • i plugged in a clean signal from another working DAC and everything is exactly the same but connecting my DAC to another ADRF6720 with the same settings and the spectrum looks better