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ADS7057EVM-PDK: External source for Single to Differential

user5802412
Intellectual 300 points

Part Number: ADS7057EVM-PDK
Other Parts Discussed in Thread: THS4551, ADS7057

Hello, 

I've bought an ADS7057EVM-PDK and download the user guide but there is one thing confuse me.

That is, ADS7057EVM-PDK use the THS4551 as fully differential amplifier so when trying to use spectral analyse tool, it seems need to give a differential signal source to J1 ( 0 ~ 3.3  ) & J2 ( 0~3.3 but have phase delay about 180 degree ).

However, why table 6 show on user guide said that we need single-ended source ?

Thank you for any suggestion and help.

BR

Wen

  • 0
    TI__Guru 51270 points
    Hello,

    This is a misprint/typo in the user's guide. It should state Differential in both the text and Table 6. You could use a Single-ended source by grounding one of the inputs for each channel (jumper J6 and J9), but you will likely see reduced AC measurements.

    Regards,
    Keith N.
    Precision ADC Applications
  • 0 in reply to Keith Nicholas
    Intellectual 300 points

    Hello Keith,

    Thank you for your suggestion.

    More question about this test environment. 

    1.Could you share what kind of Single - ended source would you recommend or TI use ?  I've tried some source and till now get the best ENOB was 12.28 bits.

    2.For 1MHz sin wave's analyze, whether it is limited by the max sample rate ( 2.5MSPS ) ?

    Thank you for help.

    BR

    Wen

  • 0 in reply to user5802412
    TI__Guru 51270 points

    Hello Wen,

    We do all of our testing using a high-end low distortion source, such as the Audio Precision 27xx series for audio band frequencies.  Unless the ADC's direct input is single ended, we always test with differential to get best performance.

    We do have a tool that we developed for TI Precision Labs training, the Precision Signal Injector (PSI).  This is a simple board that generates a clean sine wave at 2kHz and can support both single ended and differential outputs.  The typical performance of this tool is good enough to use with the ADS7057, if 2kHz is the only frequency that you need to use.  (It also supports other frequencies up to 20kHz, but the performance drops.)

    The ADS7057 is specified with input frequencies up to 1MHz when sampling at 2.5Msps; these specifications are shown in the datasheet.

    I did notice in your screenshot above that your sample rate for the captured data is only 181.82ksps.  This is due to your low SLCK frequency of 4MHz; this needs to be set to 60MHz to support the full data rate.

    Regards,
    Keith N.