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ADS131A04EVM: Attenuation after digital conversion

Part Number: ADS131A04EVM
Other Parts Discussed in Thread: ADS131A04

Hi team,

My customer was testing ADS131A04 on the EVM then he found the amplitude was a little bit lower than the analog input signal. I think it's caused by sinc filter, if so, is the attenuation level normal in this case? If you have any idea anything else please let me know.

  • Input: 2.3Vpp (0.1Vmin - 2.3Vmax, 1.2Voffset), 60Hz
  • Measured voltage on GUI: 2.254V
  • fIN/fDATA = 60/8000 = 0.0075

Regards,
Kazuto

  • Hello Tatsumi-san,

    Thank you for your post. If the data rate is configured for 8 kSPS, the digital filter attenuation at 60 Hz would be negligible. Perhaps just as a sanity check, can you ask the customer to measure the period between DRDYn falling edges and confirm the data rate is configured correctly?

    I would also suggest to measure the input voltage at the ADC input pins (after the signal chain components) on both the AINxP and AINxN pins. Is this signal measured differentially or single-ended? 

    Please share the raw data values and a schematic illustrating how the signal is measured.

    Regards,

    Ryan

  • Hi Ryan,

    It's single ended offset signal, AINxN is connected to AVSS. Before the sanity check I heard the customer got more precise data as 2.996V by using 2.442V internal reference instead of external 2.5V (REF2050).

    However I think it's too large to change from 2.254 -> 2.996 with just 0.058V different reference in 23bit resolution. What do you think?

    Additionally, is an external reference used automatically when it's connected regardless of INT_REFEN register?

    Regards,
    Kazuto

  • Hello Tatsumi-san,

    I am not understanding what are the expected input voltage and output results. Can you please clarify the input signal? What is the amplitude and frequency?

    Originally, you said this was the customer's input signal:

    • Input: 2.3Vpp (0.1Vmin - 2.3Vmax, 1.2Voffset), 60Hz -> note: if the signal ranges from 0.1V to 2.3V, that is 2.2Vpp (not 2.3Vpp)
    • Measured voltage on GUI: 2.254V -> 2.254 Vpp?
    • fIN/fDATA = 60/8000 = 0.0075

    By default, the ADS131A04 expects an external reference voltage (INT_REFEN = 0b). If the customer applies an external reference voltage to the REFP pin when INT_REFEN  = 1b, there will be some contention between the internal and external reference voltage circuits. Please avoid this to prevent IC damage.

    The VREF(V) data field in the GUI must match the reference voltage that is being used, regardless of internal or external source. Ask the customer to please check that the VREF(V) value is correct when they collect data.

    Best regards,

    Ryan

  • Hi Ryan,

    Thanks for your answer. I understood about switching reference source. The difference between displayed voltage (2.254V) and input voltage is caused by inappropriate value on VREF(V). 

    For the input signal amplitude, you are correct. This maybe just a mistake.

    Currently the issue was solved and I should close this thread. Thank you for your support!

    Regards,
    Kazuto

  • Hi Tatsumi-san - thank you for letting us know this resolved their issue! I'm glad it was a simple solution.

    Regards,

    Ryan