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ADS8688 EVM Test Problem

Shaquille Chen
Intellectual 1770 points

Other Parts Discussed in Thread: ADS8688

Hi all,

As the picture, my test for ADS8688 could not get good performance as datasheet.

Where's the possibility problem ?

I had tried external 5V dc supply with similar result.

Input signal: +- 5.12V sine wave

Input frequency: 1k Hz

  • TI__Mastermind 47365 points

    Hi Shaquille,

    Please use -0.5dBFS input signal for test and spectral analysis. This should be the reason. If still have the problem, please let us know your test setup, including your front-end components and signal source. Thanks.

    Best regards

    Dale

  • in reply to Dale Li
    TI__Mastermind 47365 points

    From: Chen, Shaquille

    Sent: Tuesday, December 08, 2015 8:50 AM

    To: Li, Dale

    Subject: RE: ADS8688 EVM Test Problem

    Hi Dale,

    Thanks for your reply.

    Could you take following picture for example?

    From my understanding, I choose input range= ±2.5 x VREF, Vin- 0.5 dBFS is equal to (±2.5 x VREF) x 0.5.

    That’s mean I can use ± 5.12 sine wave as input signal.

    It’s that correct?

    I have another question.

    What is the full amplitude and input amplitude I can get from datasheet. Is the same as Vin-0.5dBFS for input amplitude ?

    This two parameter will effect ENOB.

    ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

    From: Li, Dale
    Sent: Wednesday, December 09, 2015 12:19 AM
    To: Chen, Shaquille
    Subject: RE: ADS8688 EVM Test Problem

     

    Hi Shaquille,

    - 0.5 dBFS does not mean half of input range, the unit is dBFS. For ADS8688, you input range is ±2.5 x VREF = ±10.24V, according to the equation:       dBFS value = 20*log(voltage/dBFS_voltage), your sinusoidal wave signal for -0.5dBFS should be ±9.667Vpp. Please use this signal and test again.

    For your second question, this is a correction factor if the input signal is not the full-scale input signal, “input amplitude” is the amplitude of your real input signal. “Fullscale amplitude” is the full scale amplitude of ADC.

      

    Best regards

    Dale Li

    ----------------------------------------------------------------------------------------------------------------------------------------------------------------

    From: Chen, Shaquille
    Sent: Wednesday, December 09, 2015 5:23 PM
    To: Li, Dale
    Subject: ADS8688 EVM Test Problem Update

    Hi Dale,

     This is the updated of my measurement.

     It looks like better but not good enough.

    The attachment is my setup of measurement.

     Machine: Agilent Signal Generator 33220A

    Input signal amp: 9.667 Vpk

    Input signal frequency: 1k Hz

     

     Please feel free to let me know if there is any advice. Thanks.

    Best regards,

    -------------------------------------------------

    Shaquille

    ----------------------------------------------------------------------------------------------------------------------------------------------------------------

    From: Li, Dale
    Sent: Wednesday, December 09, 2015 7:01 PM
    To: Chen, Shaquille
    Subject: RE: ADS8688 EVM Test Problem Update

     

    Hi Shaquille,

    Absolutely you can not get good performance test result because the quality of your signal source is much worse than ADS8688, for example, Harmonic distortion:

    33220A:     -70dB

    ADS8688:   -102dB

    You need a pure high quality signal source.

    Best regards

    Dale Li