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ADC09QJ800: Lower limit on sample frequency

David Wende
Intellectual 620 points
Part Number: ADC09QJ800
Other Parts Discussed in Thread: ADS54J66

This part seems a perfect fit for our next project in terms of $ and performance.

Except - that we require only 210 MSPS and this device is spec'ed at 500 MSPS minimum.

Of course, we could just decimate in the FPGA, but this would mean dissipating extra thermal power that we don't really need.

Is this a hard lower limit?

Is there another similar device that could sample down to 210 MSPS?

Thanks

  • 0
    TI__Mastermind 21065 points

    Hi David,

    I am not familiar with this device myself, however I would expect this lower frequency limit for the sample clock is not actually a hard limit. If similar to our other JESD devices, as long as the serdes lanerate is above the output transceiver's minimum specified value (in this case 2.5Gbps) then I would expect the device will operate at lower sampling rates. Please note that the primary engineer covering this device is out of office for 2 weeks, so I will try to check with others on our team to see if they may know. Stay tuned.

    Regards, Chase

  • +1 in reply to Chase W
    TI__Mastermind 21065 points

    Hi David,

    It turns out this is indeed a hard lower limit on the sample frequency due to the way this device is architected.

    If you must avoid decimation in the FPGA, might I suggest to look using into the ADS54J66. This device can sample down to 250MSPS in decimation bypass mode, however, this device does supports on-chip decimation meaning you can sample at 420MSPS in a decimation by 2 mode yielding the 210MHz output data rate you are requiring. The benefit of this approach is utilizing the low pass decimation filter to assist in out of band spurious rejection as the stopband attenuation spec is near 90dB of rejection/attenuation. The downside is that a higher sample clock frequency is required but also you will find a reduction in IBW: The -1dB cutoff occurs at fs*0.216 ≅ 91MHz. If the BW reduction is too much and the sample clock is flexible, simply increase the sample rate to increase this BW. Unfortunately, we don't have any other devices comparable to ADC09QJ800 at this same price point in our portfolio. The ADS54J66 is the closest which I have been able to find. I hope this helps!

    Regards, Chase

  • 0 in reply to Chase W
    Intellectual 620 points

    Thanks for the prompt reply.

    The ADS54J66 is certainly a technical option but it's a bit pricey.

    david