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DAC38RF89: There is near - end spurious in DAC38RF89 output

Yunlong Zhao
Prodigy 20 points
Part Number: DAC38RF89
Other Parts Discussed in Thread: LMK04828

The DAC output is 1100MHz. There are spurious of 1M and 37.5M, respectively.

The PLL configuration of the DAC is as follows：0x31 0x0400；0x32 0x0508；0x33 0x2A24.

The DAC clock is 200MHz of differential input.The VCO frequency is 4800MHz.

I can't find the source of the spurious at the moment, I hope you can give me some inspiration.

Thanks,

Yunlong.

  • 0
    Prodigy 20 points

    The DAC clock source is LMK04828.In the previous test, I connected the clock output of LMK04828 to the spectrometer for testing, but there were no spurious of 1MHz and 37.5MHz.

    LMFSHd=82121.The spurious of 1MHz and 37.5MHz follows the DAC output frequency, but the relative position remains constant.The SPI clocks have all been turned off.Sysref has also been turned off after synchronization.After the above efforts,there are still spurious of 1M and 37.5M.

  • 0 in reply to Yunlong Zhao
    TI__Guru 66054 points

    Hi Yunlong,

    The 1MHz spur may be caused by DC-DC converters on your PCB. Please check if you have any DC-DC switching frequency around 1MHz. 

    The DAC itself does not generate the 37.5MHz spur. Please see if you can use the RF probe to probe around the board as an antenna to see if you can "sniff" any components that generates 37.5MHz spur.