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ADC3444: Acceptable intermediate frequencies

XIN LI
Prodigy 180 points
Part Number: ADC3444
Other Parts Discussed in Thread: ADC3443

Hello, 

My team has chosen ADC3444 for IF sampling application for a 25kHz BW signal. We will use it for 1-wire LVDS configuration, i.e. 80MSPS max. I would like to know if this Quad-Channel ADC can accept the following IF signals: 10.7MHz, 16.9MHz, 21.4MHz and 45MHz. Which sample rate I need to choose in this ADC for the mentioned frequencies ? 
Thanks in advances for your help,
XL
  • 0
    TI__Genius 12780 points

    Hi XL,

    The ADC3444 will be able to sample all of the IF signals that you have listed.If you sample at 80 MSPS, the 45 MHz IF will "fold" back to 35 MHz since it would be in 2nd Nyquist zone, so I think that will probably be ok in terms of frequency planning.

    Best Regards,

    Dan

  • 0 in reply to dBrock
    Prodigy 180 points

    Hi Dan,

    Thanks for your help.

    I'm wondering if I would have problems when I use 45MHz intermediate freuqnecy. My question is, if I use 45MHz, the signal will fold into the 1st Nyquist zone, but I could do overs-ampling any more because 35MHz x 2 = 70MHz < 80MHz, just twice the Nyquist rate. This respect theory of Shannon but it will not improve the resolution and the SNR compared to oversampling (N for oversampling factor, thus SNR increased by sqrt (N)). Do I need to reduce the IF frequency to improve the performance ? Am I wrong or I'm missing something ?

    Thanks in advances,

    Best regards,

    XL

  • 0 in reply to XIN LI
    TI__Genius 12780 points

    Hi XL,

    I believe you are correct, but, as the input frequency increases, the SNR degradation will be dominated by the phase noise/jitter of the sampling clock and aperture jitter of the ADC. If you look at the difference in performance between 10 MHz and 70 MHz, there is only about 0.1 dB difference in SNR

    Also, if you look at the ADC3443 AC performance specifications (80 MSPS), it also has a difference of about 0.1 dB between 10 MHz and 70 MHz.

    My suggestion is that you do not need to modify these frequencies if you are concerned with performance.

    Best Regards,

    Dan

  • 0 in reply to dBrock
    Prodigy 180 points

    Hi Dan,

    Thank you so much for resolving my issue.

    Have a good day,

    Best regards,

    XL