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DAC3482: DAC3482 output signal spectrum have sideband

Part Number: DAC3482
Other Parts Discussed in Thread: TPS54227, TLV62565, DAC3484

Hi team,

My customer is using our DAC3482 in a signal generator project. We measured the spectrum of the output signal and found there are side band signals around.

Test condition: 

1. input clk=500MHz, PLL=2 so DACCLK=1GHz

2. Datarate=500Msps, interpolation=2 so sample rate=1Gsps.

3. NCO is shutdown

When we set the output signal frequency to 10MHz, the spectrum is as below: The central frequency(maker 1)=10MHz, -20.169dBm. The side band signal (maker 3/maker 2) is=10.008MHz, -72.958dBm / 10.017MHz, -77.146dBm

When we set the output signal frequency to 20MHz, the spectrum is as below:  The side band signal is=20.008MHz, -68.069dBm / 20.017MHz, -72.019dBm

So can you help analyze why the side band signal will show up and how to get rid of it? Thanks.

Best regards,


  • Hi Wayne,

    These type of double sideband modulation are typically due to the following:

    1. power supply switching frequency coupling

    2. OSTR clock frequency coupling.

    The coupling frequency is at 80KHz and 160kHz. This is very typical of the power supply switching frequency. Please check if the customer's system have any DC/DC switching supplies operating at such frequency, and add additional filtering to the DAC supply rails

    The OSTR source can be turned off when not used. They can try to disable OSTR signal and recheck the spectrum.

    Please also check other sources that can create the 80kHz and 160kHz spur.


  • Wayne,

    I am closing this thread for now. You can always reply back to re-open this issue.


  • Hi Kang,

    Thanks for your advice. I checked below points based on your instruction:

    1. DAC3482 power supply:

    The DAC3482 power supply filter schematic is as below. VP3V3 is provided by TPS54227 and VP1V25 is provided by TLV62565. What's more, in the previous thread picture, the frequency of the sideband  is 10.008MHz and 10.017MHz which means the coupling frequency is 8kHz and 17kHz instead of 80KHz and 160kHz. So 8kHz and 17kHz is far away from DCDC switching frequency and I thought customer already have enough filter parts on the power rail. So I thought the sideband is not related to power supply issue.

    2. About the OSTR, customer didn't use this signal, can you please help check which register is used to disable the OSTR signal? I didn't find it in our datasheet.

    3. We suspect the side band is related to DAC3482 PLL, so we measured the spectrum in below configuration:

    500MHz clk input—>DAC3482 PLL bypass—>500MHz DAC clk

    500Msps datarate—>interpolation=1—>500Msps sample rate

    Under this configuration, the spectrum is as below, the sideband is gone. So can you help check if the sideband is related to PLL? How to adjust the PLL setting to avoid the sideband?


    Best regards,


  • Wayne,

    the DAC3484 itself does not generate these tones at 8kHz and 16kHz. It is fully characterize to not do so. If it does, we will have big problems.

    The 8kHz and 16kHz could be due to multiple DC/DC supplies have modulating itself. For instance, if one DC/DC supply is at 100Mhz, and another at 100.008kHz, then you can have 8kHz modulating on top of the DAC output. 

    The 8kHz is too hard to be filtered out through convention LC filters. It has to be mitigated through layout. 

  • closing the post for now until further inquiries.