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ADS1299EEG-FE - Question regarding external reference voltage

Alexander Zorn
Prodigy 70 points

Other Parts Discussed in Thread: ADS1299

In the user guide for the ADS1299EEG-FE, it mentions that the footprints for an external reference are provided on the board but not populated. Are there any sample schematics with part numbers / passive component values that could be provided for reference? We are trying to play with the external reference voltage so that we can optimize the A/D resolution with respect to our input signal.

Please and thank you!

Alex

  • 0
    TI__Mastermind 23235 points

    Mr Zorn -

    Please have a look at FIgure 31 in the ADS1299 datasheet and see if that provides information that helps.

  • 0 in reply to Greg Hupp
    Prodigy 110 points

    I also have the same issue.The EVM docs warn that “For high-end EEG systems, the capacitor values should be chosen such that the bandwidth is limited to less than 10 Hz so that the reference noise does not dominate system noise.”

    So... does this mean that this has been done on the EVM using the internal ref or that the user should use the External reference set up indicated in the datasheet and provided (sort of) in the EVM PCB?

    The PDK provides a schematic showing the "no installed" parts and a partlist for the EVM but the missing parts are listed with no part#s.

    Checking the datasheet Fig31 gives clues to most parts but is not an exact match for the PCB schematic Fig 62. In particular 2 additional resistors are added on the opamp input and the footprint for the 100uF cap (datasheet) that would be C39 on the EVM seems small.

    What's the difficulty in simply providing the BOM info that the PCB was laid out to???

    Jim

  • 0 in reply to Jim Boyd
    TI__Mastermind 38745 points

    Hi Jim,

    The EVM was designed to provide users with a great deal of flexibility in their development process. There was no specific reference driver in mind when the board was spun with the idea that the user could try different options with the footprints provided. Though the figure in the datasheet suggests a particular reference drive circuit, the EVM was not designed with that particular reference drive circuit in mind. I apologize for the confusion. Let us know if you need help deciding on a reference drive circuit.

    Regards,

    Brian Pisani