AD9251 DCOA/B with Interleaved Outputs

When running the AD9251 with interleaved output data multiplexed onto a single bus, the respective A channel or B channel data is output for only ½ the clock period. 

In this case, should we expect to see a rising edge on DCOA to indicate valid Channel A data and then a similar rising edge on DCOB approximately ½ a clock period later to indicate valid Channel B data?  This is not clear to us from the timing diagram shown in Figure 3 of the datasheet.

And, should the rising edge occur roughly during the midpoint of the valid data?  According to the figure, the rising edge occurs closer towards the tail end of the valid data.  Should the frequency of DCOA/B be the same as the frequency of the CLK+?

Thanks.

  • Hi-

    I moved this question about the AD9251 to the High-Speed ADCs community.  Someone here should be able to assist you.

    Regards,

    AndyR

  • Hi Doug,

    Thanks for your response.

    Would you recommend using the rising edge of DCOA/DCOB to clock in the CH-A data and the immediate corresponding falling edge of DCOA/DCOB to clock in the CH-B data?

    Regards,

    NNIS

  • 0
    •  Analog Employees 
    on Oct 9, 2012 7:34 AM over 8 years ago

    Dear NNIS,

    Regarding your first question, DCOA and DCOB are are not skewed in time from each other by default. In other words, a rising edge on DCOA will be coincident with a rising edge on DCOB in the default condition.

    These rising edges will occur at close-to-the-same time as the data edge, and not at the mid-point of valid data, in the default condition. This is an as-designed characteristic that is typically handled by the capturing FPGA or ASIC.

    And yes, the frequency of DCOA and DCOB will be the same frequency as the sample clock.

    I hope your project goes well. Please let me know if you need more information.

    Take care,

    Doug

  • 0
    •  Analog Employees 
    on Oct 9, 2012 9:01 AM over 8 years ago

    Hi NNIS,

    If you are asking if you should use a rising edge to capture one channel's data, and the following falling edge to capture the other channel's data, the answer is yes.

    If you are asking about using the rising edge to specifically capture channel A data, the answer depends on how you set up the timing in your capture environment. According to the datasheet timing diagram, the rising edge of DCO will be coincident with the end of valid ChA data. Conversely, the falling edge of DCO will be coincident with the start of valid ChA data.

    In my experience, using the rising edge of DCO to capture previously valid Channel A would be the more common scenario (positive setup time, close-to-zero hold time). But, you can choose either edge depending on the timing setup of your capture environment.

    I hope this helps. Let's continue the dialog if more information is needed.

    Thanks,

    Doug