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ADC12J4000: Spur at Fs/4

Part Number: ADC12J4000
Other Parts Discussed in Thread: ADC12DJ3200

Hello again!

During last experiments with adc12j4000, we encountered unexpected behavior of device.

ADC produces significant spur at Fs/4. It happens in different modes (bypass, dec x4, dec x8, etc.).

Why it is critical? We want to use built-in NCO with frequency preset at Fs/4.

After checking out different register settings, we discovered that it looks like it’s not our mistake and looked into the web and found that topic:

But actually we can’t say that topic solves out problem. Could you help us to overcome that trouble?

  • Hi Alera

    The expected value of the spur at Fs/4 and other interleave related spurs are included in the Electrical Characteristics table on page 11 of the datasheet. If the device is calibrated properly you should see spurs at levels similar to this. If you are seeing higher spur levels please let us know and we can help debug the cause.

    If you cannot tolerate any significant spur at Fs/4 you could consider the similar ADC12DJ3200 device. This is a dual/single input device. In Dual Input mode each input is sampled by 2 interleaved converters, so there is no spur at Fs/4. In Dual Input mode there are also similar DDC features available. The only limitation is the maximum sample rate will be 3200 MSPS instead of 4000 MSPS as with the ADC12J4000.

    I hope this is helpful.

    Best regards,

    Jim B