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Interpretation of ADS42JB69 ENOB/SNR

Peter DeVore
Prodigy 40 points
Other Parts Discussed in Thread: ADS42JB69

Hello TI,

On page 4 of the ADS42JB69 datasheet, the chip gets 12.1 ENOB at 2.5 Vpp full scale, and the SNR improves from 74.7 dBFS at 170 MHz to 75.6 dBFS at 70 MHz. If I have a broadband signal from 0 to 125 MHz, is it possible to filter out the frequencies above the Nyquist bandwidth (i.e. 125 to 900 MHz, as the highest sampling rate is 250 MSps) to improve this value? If not, then if I have a 0 to 125 MHz band limited signal at the input, will chip yield at least 74.7 dBFS SNR?

Peter

  • 0
    TI__Genius 9695 points

    Hi Peter,

    The SNR in datasheet only considers the noise power within the Nyquist bandwidth so filtering the noise above Nyquist will not affect this value. At 170MHz, the SNR is calculated using the aliased signal at 80MHz (see figure 7 on pg 13 of datasheet)

    Also SNR of 74.7dBFS is the typical value, most parts will show this SNR, and not the guaranteed minimum SNR.

    Thanks,

    Eben.