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ADS4149: What happens to the processing gain when spurs and distortion products are included in the bandwidth (BW)?

Danilo A.
Mastermind 27790 points
Part Number: ADS4149

Hi Team,

We would like to ask your help regarding our customer's inquiry below.

I am reviewing app note SLAA594A - June 2013 - Revised 2013. I have a question on section 3.1 (page 6) of this app note. Question: what happens to the processing gain when spurs and distortion products are included in the bandwidth (BW)? The greater the sampling rate, the more distortion is possible in-band. Do you have an app note that describes this effect?

Regards,

Danilo

  • 0
    TI__Mastermind 33340 points

    Hi Danilo,

    Not sure I completely understand your question. If spurious are located in the BW of interest, there could be degradation too. But in theory you would have an increase in SNR because you are only using just a portion of the BW.

    The greater the sampling rate, the larger the Nyquist zone, ie - larger the BW. Not sure I agree with more distortion is possible, it depends. Please elaborate and I will see what I can find.

    Regards,

    Rob

  • 0
    TI__Intellectual 1880 points

    Hi Danilo,

    Thanks for referring to my app note. The processing gain advantage is still exist even if there are spurs within the band. Let me explain using the App note example. Sampling rate of ADC is 200MSPS and Signal Bandwidth BW is 20MHz. Say SINAD is X in the full Nyquist Bandwidth (100MHz) of ADC. With the processing gain i.e. using DDC to filter out all the band except the bandwidth needed (20MHz), processing gain advantage is 7dB and overall SINAD is X + 7.  In another possibility where spurs/distortion is out of this BW, then the SINAD is again X in full Bandwidth and  after decimation/filter using DDC etc,  SINAD is still X + 7 or little higher within the band of 20MHz. In short, the Processing gain advantage exist.