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ADS1298 for EEG measurement.

Ahnsei Shon
Prodigy 215 points
Other Parts Discussed in Thread: ADS1298, INA118, INA333, INA128

Is there futher information(Application note for EEG like Circuit ) to use ADS1298 for EEG measurement?

I now that EEG signal is smaller than ECG approximately 20times.

So, I think another gain amplifier is need at the front end.

Does ADS1298 work exactly without another amplifier to detect EEG signal?

 

  • 0
    TI__Guru**** 180931 points

    Hi Ahnsei,

    The ADS1298 is a little noisy to be used directly with EEG, as you noted, you would have to gain up the input via a pre-amplifier stage.  We are working on a solution to this but in the meantime, please feel free to review this app note: http://focus.ti.com/lit/an/sbaa160a/sbaa160a.pdf

     

  • 0 in reply to Tom Hendrick
    Prodigy 215 points

    Thank you for your advice.

     

    I have another question for using ADS1298 about EEG measurement.

     

    In this case what I have to do with WCT(pin64), paceout(pin17,18) and etc  which is not related with EEG measurement pins. 

     

    Should I have to connect those pins with AGND, DGND, or OPEN which one is recommended from you?

     

  • 0 in reply to Ahnsei Shon
    TI__Guru**** 180931 points

    Hi Ahnsei,

    The WCT (pin 64) is an output - that one you can leave open along with the two pace_out pins.  Leaving analog or digital output pins open is generally fine.  Any unused inputs sould be terminated though.  You could put resistors to GND or hard tie them.

  • 0 in reply to Tom Hendrick
    Prodigy 215 points

    AS you know, I'm trying to make EEG circuit with ADS1298.
    There is no recommended and adequatable circuit for this.
    I am modifing your ECG demokit circuit(ADS1298ECG-FE).
    I know AGND and DGND should be separated.
    But in your circuit, it is connected together.
    I qurious about how to treat AGND and DGND.
    Separate or Connect together?

    ----------------------------------------------------------
    Always, I appreciate your advices.
    Thank you.

  • 0 in reply to Ahnsei Shon
    Prodigy 40 points

    Hello Shon,

    I need to make an EEG too and I was thinking about making it using the ADS1298. I think it could be a could idea to modify the demokit ADS1298ECG. Could pass me direct contact yours, in order to divide ideas easier?

  • 0 in reply to Ahnsei Shon
    TI__Guru**** 180931 points

    Hi Ahnsei,

    Actually our board has a segmented ground layer.  I also just noticed that there is an error in the users guide - Figure 65 is the ground layer, and Figure 64 is the power.  At some point in the board, the AGND and DGND need to reference each other.  On the EVM, the power comes into J4 and the analog/digital grounds are on pins 5 and 6.  Pin 5 is DGND and ties back to AGND via R89.  The lines  you see in the ground layer are void of copper and help to ensure the noiser 'agnd' return currents around the BGA are kept away for the analog input signals.  So - essentially the grounds are seperated in the PCB, but still referenced together back at the power supply.

  • 0 in reply to ravissonsf
    Prodigy 215 points

    If you want to contact me, use following e-mail address. ahnsei@gmail.com

    Thank you.conn

  • 0 in reply to Tom Hendrick
    Prodigy 45 points

    Hello Tom, I have read the app note about Analog Front-End Design for ECG Systems Using Delta-Sigma ADCs. It is helpful. Thanks.

    For EEG use of ADS1298, do you have some advice how to design the preamplifier with single 3.3V supply?

    Some example application schematics woult be great help. Thank you in advance.

    Regards

    Adam Wolf

    adam.wolf (at) ee.oulu.fi

  • 0 in reply to Adam Wolf
    Prodigy 45 points

    ... Actually I don't know how to correctly connect the RLD (right leg drive) if the input signal is preamplified. I suppose there shoud be another amplifier with gain reciprocial to the preamplifier or a divider (?).

  • 0 in reply to Adam Wolf
    Prodigy 45 points

    Ok. I have found the answer here (page 11 below):

    http://focus.ti.com/lit/ds/symlink/ina118.pdf

    A.

  • 0 in reply to Adam Wolf
    TI__Guru**** 180931 points

    Hi Adam,

    Sorry for the slow response, yes, the INA118 is a good option.  You might want to take a look at the INA128 and INA333 as well.

  • 0 in reply to Tom Hendrick
    Prodigy 20 points

    So, the ads1298 doesn't work for EEG? Datasheet

    Datasheet said in the overview part  that ads1298 can be used for EMG, is that truth? Or have too noise for measure EMG signals?

    Thanks.

  • 0 in reply to Mariano Catalini
    TI__Expert 3260 points

    Hi Mariano,

    The datasheet (tables 1-4, 3 in particular) states that the noise floor could be as high as 483µV. This, of course, depends on data rate, gain settings of the PGA, and Analog supply & Reference voltages. So, for signals below this, a prestage amplifier is needed. As you may already know, typical EMG signals are in the µV range (in some cases, the maximum is 5mV). The ADS1298 is not designed to work directly with EEG/EMG amplitudes, but is designed to process the signals.

    So, the simple answer is yes, the part can be used for these signals, assuming a prestage amplifier is used to raise the signal above the noise floor. Once done, the chip is perfectly adequate for EEG/EMG signal processing.

    Best Regards,

    Michael

  • 0 in reply to Michael W
    Prodigy 20 points

    Michael thanks for the answer.

    I'm working in a project that i have to acquire EMG/EEG/ECG, and ADS1298 is a good device for do that.

    I think is very important the information that you give me appears in datasheet.

  • 0 in reply to Tom Hendrick
    Prodigy 50 points

    Hi Tom,

    Is there any  Evaluation board for these Amplifiers ( INA118,INA128, INA333) ?

    I too have a requirement to design an EEG board.   Would prefer to use low noise front end  boards if it is already  available   from TI or any third party ?

    regards,

    Anil K S.

    AneHAs Technovations, India.

  • 0 in reply to Tom Hendrick
    Prodigy 50 points

    Hi Tom,

    Has TI completed  the development of the solution what you mentioned here  ( Pre Amplifier Stage for  ADS1298 for EEG Applications ) ?

    regards,

    Anil K S

    AneHAs Technovations, India

  • 0 in reply to Anil k S
    TI__Guru**** 180931 points

    Hi all -

    The EEG signal levels are smaller and ideally a gain stage ahead of the ADS1298 would be used to boost the signal levels, at the moment I don't have any specific option or add on board that would show you the best results - each system is going to be a little different so having a one size fits all won't really be possible.  That being said, I am willing to investigate producing an INA/PGA add on card that would perhaps plug into the existing ADS1298 ECG-FE board.  Lets say the shunt jumpers from JP30 thru JP37 were comepletely removed and you had the ability to mount a pre-amp stage right onto those headers.  What would you want to see?  What gain option(s)?  Is power a concern to you?

  • 0 in reply to Tom Hendrick
    Prodigy 45 points

    Hi, can you give me an advise, how to handle with RDL pins of AD1298 if I use a signal preamplifier? I have done the patient right left drive signal in the preamplifier stage. Is it posible to use it for Lead-Off Detection feature of the AD1298? Can you please describe, how to connect it correctly?

    My actual schematic for EEG front-end is here:

    http://canku.mawadani.cz/eeg.pdf

    Thank you in advance!

    Regards.

    Adam Wolf.

  • 0 in reply to Anil k S
    Prodigy 20 points

    How does one do patient protection in an isolated EEG amplifier if it is DC connected?  The auxiliary current is limited to 50uA in single fault condition.  What if the fault is a short  between the supply volts and one input of the amplifier chip? Can a chip fail like this?

  • 0 in reply to DE Maynard
    TI__Guru**** 180931 points

    Hi DE,

    Welcome to the E2E forum!  Normally there would be series resistors to limit the current in the case of an amplifier input shorting to the rails.  Some EEG/ECG cable vendors actually embed series resistors in the actual cable as well to limit the amount of current that can flow in the leads.  Please consider starting a new thread by using the 'New Post' option if you have additional questions.

  • 0 in reply to Tom Hendrick
    Prodigy 20 points

    Sorry. That won't work.  If I have to limit current between two electrodes to less than  50uA, with an amplifier  short to one terminal of a +-2.5 volt supply, the resistor size would be >25k in each lead.  This would generate too  much noise.  The amplifier would not be good for looking  at low amplitude EEG.  OK I will start a new thread if I want to take this further.

  • 0 in reply to Tom Hendrick
    Prodigy 25 points

    Hello sir,

        I am a new user of this platform.Even am working on same concept using ads1298 but not for all 20 leads in EEG but only with respect to few leads according to my usage.Can you please refer me with some suggestions so that i will get maximum benefit.

    Thanks.