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ADC selection

Yoonsun Kim
Expert 1850 points
Other Parts Discussed in Thread: ADS42JB69, LMH6882, LMH6521

Hello,

I am in trouble for selection ADC.

The signal range to my board is 0 ~ - 90dBm, thus I think ADC's specification should be 16-bit resolution and over 90dB SINAD.

However I cannot find any ADC which SINAD is over 90dB among the high speed ADCs.

Can you let me know the order priority of parameters?

 What parameter should be considered first?

  • 0
    Expert 2585 points

    Hi,

    Could you clarify  the inputs.

    1) What speed (sample rate) you need from ADC. And do you really need 16-bit resolution

    2) What type of the input (differential, single ended) do you need?

    3) What is voltage input range for your application?

  • 0 in reply to Oleksiy Pazyuk
    TI__Genius 17320 points

    Hi,

    The bandwidth of your signal will be a key parameter. If you have a narrow band signal, then over sampling can improve the in-band SNR performance by distributing the quantization and thermal noise over the entire Nyquist zone. It is then assumed that digital filtering would be used to eliminate noise outside of your band of interest and frequency planning would be used to avoid spurious signals within your band.

    Let's consider the ADS42JB69. It's SNR performance at 170 MHz is 73.3 dBFS, meaning the total noise is -73.3 dBFS. This noise is spread over the whole Nyquist zone (125 MHz assuming 250 Msps is used), so we can define the noise floor as:

    NF = -73.3 dBFS - 10log(125MHz) = -154.3 dBFS / Hz

    The full scale input of the ADS42JB69 is 10 dBm (2 Vpp @ 50Ω), so you would be operating from -10 dBFS to -100 dBFS. You can then define your in-band SNR as:

    SNR = Psig - (-154.3 + 10log(BW))

    Where Psig is your signal power, and BW is your signal bandwidth. If you want a minimum in-band SNR of 6 dBc then the maximum signal BW that will achieve this is 67.6 kHz. For wider bandwidths you will need an amplifier in front of the ADC to achieve sufficient performance. For such a wide input range a DVGA would likely be the best choice. For low frequency applications the LMH6882 is a good choice. For higher frequency applications the LMH6521 is a good choice.

    Regards,
    Matt Guibord