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ADS8866: About the ADS8866 Vref/2 causing noise

Anthony
Prodigy 150 points
Part Number: ADS8866
Other Parts Discussed in Thread: MSP430FR5994

Tool/software:

Hello, TI expert,


I have a project for a special application of sound collection (200Hz ~ 5 kHz); the specification of sound collection is 50 kSPS, ADC 16 - bit. Currently, MSP430FR5994 with a 16 MHz clock and ADS8866 can meet my needs, but I encountered a problem. I set the DC Offset to Vref/2 voltage value, but the sound obtained has a lot of noise. I attached the circuit diagram, please give me some advice, Thank you.

  • 0
    TI__Expert 8625 points

    Hi Anthony,

    Thanks for your post. Do you mean you added 1.25V of DC offset to your "ADInput" signal? What is the full range of your input voltage now? Could you share a screenshot of an oscilloscope capture of your input voltage and describe the noise at the output of the ADC?

    Best regards,

    Samiha

  • 0 in reply to Samiha Sharif
    Prodigy 150 points

    Hi Samiha,


    You are right. ADInput has added DC offset 1.25V and it is completed at the red frame of OPA. Now I have adjusted Vref to 3V and DC offset to 1.5V. The results obtained by oscilloscope do not seem to exceed the critical voltage. There is still a lot of room. Noise is still generated. Attached is the wav file.

     


    The manual mentions that a Buffer needs to be added after the Voltage Reference for use with the ADC REF. This is what I have seen so far.


    Best regards,

    Anthony.

     

  • 0 in reply to Anthony
    TI__Expert 8625 points

    Hi Anthony, 

    Good catch. It is likely that the REF33xx is introducing noise. In the datasheet, we recommend using the REF33xx with an additional buffer circuit:

    Alternatively, you could use the REF60xx, which has much lower noise than the REF33xx, so does not really require an additional reference buffer stage:

    The datasheet application section and device EVM schematic can act as good resources for component selection and schematic design.

    Best regards,

    Samiha