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DAC38RF87: Interpolation and Composite Magnitude Response

Kei Kuwahara
Expert 7680 points
Part Number: DAC38RF87

Tool/software:

Hello team,

I am confused about the interpolation of high speed DAC.

On the datasheet, there are several Magnitude Respose for each interpolation factors.

The lower interpolation rate (6x vs 24x) seems to have wider flat band response.

I thought higher the interpolation result wider flat band for output because more over sampling.
Why does lower interpolation factor result wider band?

Best Regards,
Kei Kuwahara

  • 0
    TI__Guru* 78584 points

    Hi Kei,

    You may refer to the following app note:

    https://www.ti.com/lit/an/slaa523a/slaa523a.pdf

    The final DAC rate remain the same for all interpolation stages. With higher interpolation ratio, the interface rate (interface between FPGA and DAC) can be reduced. Therefore, the interface rate with lower interpolation has wider bandwidth, and interface rate with higher interpolation has lower bandwidth. You want the minimum amount of interface rate needed for your application to reduce interface constraints. 

    -Kang

  • 0 in reply to Kang Hsia
    TI__Expert 7680 points

    Hello Kang-san,

    Thank you for the explaination.

    I have a new question poped up.

    The flat band of this FIR response is only up to 0.075 (f/FDAC)
    My customer would like to output 1GHz sine wave with 4GSPS of FDAC, but this is 0.25 (f/FDAC) I suppose.
    I am afraid it will be outside of flat band of SINC filter, and 1GHz output will be attenuated to -100dB.

    Can DAC38RF87 output 1GHz sine wave without much attenuation?

    Best Regards,
    Kei Kuwahara

  • 0 in reply to Kei Kuwahara
    TI__Guru* 78584 points

    Hello Kei-san,

    There is a difference between RF range and RF bandwidth. For example, the above interpolation ratio with 4GSPS DAC will support about 300MHz of bandwidth (interface bandwidth between customers digital ASIC to our DAC). The customer may use our NCO and complex multiplier to shift the 300MHz of bandwidth to 1GHz location (RF range)

    The 300MHz is the RF bandwidth, while the RF range is 1GHz. The 1GHz RF range is extended by the NCO

    The above information can be referenced in the app note above.

    -Kang