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ADS58B18 related questions

John J Wu
Genius 3870 points
Other Parts Discussed in Thread: ADS58B18

We are looking at the ADS58B18. I need some help here: we are trying to understand the SNRBoost gain at 75MHz BW. Does this ADC even can be set for 75MHz BW?

According with the datasheet:

“Using SNRBoost, enhanced SNR can be obtained for any bandwidth (less than Nyquist or fS/2;…)”

however things get a bit confusing according with the Table 9 and 10 (page 49/69 of the ADS58D18 datasheet…)

 

  • 0
    TI__Genius 17290 points

    Hi John,

    To achieve 75 MHz of bandwidth, you must choose your corner frequencies appropriately. The corner frequencies are set by the coefficients in table 9, of which there is a limited number of options. Table 10 is just an example of how to set the corner frequencies to achieve a desired center frequency. Take the case below:

    Fs = 200 MSPS
    Fcenter = 50 MHz
    BW = 75 MHz

    Fc1 = Fcenter - BW/2 = 12.5 MHz
    Fc2 = Fcenter + BW/2 = 87.5 MHz

    Fc1 / Fs = 0.0625
    Fc2 / Fs = 0.4375

    Due to the limited coefficients, choose the closest values. So Fc1 is chosen to be 0.08 (0x9) and Fc2 is chosen to be 0.42 (0x7), as in the last row of table 10. This places the bottom of the bathtub from 16 MHz to 84 MHz.

    Regards,
    Matt Guibord