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DAC3484: DAC3484 Output Spur Issue

HENRY JUNG
Expert 2030 points
Part Number: DAC3484

Dears.

cutomer use DAC3484.
The setting values of the DAC are as follows.
DAC CLK : 138.24Mhz
Interpolation : x4

When the internal PLL is set, a spur occurs on the output.

We changed it to External because it is thought that spur occurs due to the influence of internal PLL.

External mode is set and output waveform is as follows.
register value Review.
What are NCO settings and solutions?

Register Value


x"00" x"F498",
x"01" x"040E",
x"02" x"F05A",
x"04" x"B7C0",
x"05" x"3F78",
x"24" x"0000",
x"0c" x"0500",
x"0d" x"0500",
x"10" x"3000",
x"20" x"4801",
x"00" x"F298",
x"15" x"2800",
x"1f" x"4446",
x"1f" x"4442",
x"0f" x"0400",
x"03" x"C000",
x"03" x"F000",
x"18" x"246f",
x"19" x"0804",
x"1a" x"7c10",
x"00" x"F498",
x"24" x"0000",
x"25" x"7A78",
x"26" x"B6B6",
x"2d" x"0004",
x"2e" x"0000",
x"20" x"4801",
x"00" x"F29C",
x"15" x"3000",
x"1f" x"888A",
x"1f" x"8888",
x"0d" x"05A6"

Thank you.

  • 0
    TI__Expert 4880 points

    Hey Henry,

    There could be a few things wrong here. I tried mimicking your setup as best as i could and i do not see output spurs nearly as high as yours. I cant tell what your RF output power is but it looks like it is possible that you are overdriving the spectrum analyzer with such a low reference level. On my end, even when i over saturated the spectrum analyzer i still didnt get spurs quite as high.

     I dont really have clear enough information from you to fully determine what the problem is. But once you provide the following paramters i will send you a config file that should help get you going.

    What is the desired.

    Dac clock frequency?

    Interpolation?

    NCO frequency?

    Baseband input frequency?

    RF output power?

    Yusuf