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VREF in AD9695

Category: Hardware
Product Number: AD9695

Hi,

In our system, we have our analog front end IC board to drive the analog input of the AD9695. We want to use dc-coupled connection so the output stage of our front end circuit needs to provide the same common-mode (CM) voltage as the input CM of the AD9695, which is 1.41V as stated in the datasheet. I notice that your AD9695 provides a input/output called "VREF", and I read through the description but still have some questions.

The main question is that: Can I use this VREF as a reference 1.41V CM voltage for our output stage common-mode feedback circuit? If I understand the following picture correctly, I can control the SPI registers and export a 1.41V voltage reference through this pin? Thanks!

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  • Hi jamesjjc,

    Your query is acknowledged and will be responded by the product owner soon.

    Regards,
    Peevee

  • Hi Jamesjjc,

    Yes, an on-board common-mode voltage reference is included in the design and is available from the VREF pin.
    Using the VREF output to set the input common mode is recommended, please follow the instructions as described in the datasheet.

    The output common-mode voltage of the ADC driver is easily set with the VREF pin of the AD9695 via SPI.

    Please refer to below registers writing:

    WriteRegister(0x1908, 0x04);

    WriteRegister(0x18A6, 0x00);

    WriteRegister(0x18E6, 0x00);

     

    WriteRegister(0x18E0, 0x02);

    WriteRegister(0x18E1, 0x14);

    WriteRegister(0x18E2, 0x14);

     

    WriteRegister(0x18E3, 0x40);

    WriteRegister(0x18E3, 0x5E); buffer current setting depends on final application.

    Regards,

    Alvin

  • Hi Alvin,

    Thanks for your explanation. So is this exported VREF a 1.41V CM voltage? Because I see somewhere in the datasheet says that it's a 0.5V CM voltage.

    Thank you.

  • Hi Jamesjjc,

    Yes, the exported common-mode voltage to the VREF pin is around 1.4V by above SPI writing. The AD9695 input buffer offers flexible controls for the analog inputs, such as, buffer current, the input common mode voltage will slightly change based on the buffer current setting.

    Regards,

    Alvin

Reply
  • Hi Jamesjjc,

    Yes, the exported common-mode voltage to the VREF pin is around 1.4V by above SPI writing. The AD9695 input buffer offers flexible controls for the analog inputs, such as, buffer current, the input common mode voltage will slightly change based on the buffer current setting.

    Regards,

    Alvin

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