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ADS1299

Hayden
Prodigy 20 points
Other Parts Discussed in Thread: ADS1299

Hi There,


We have a few questions regarding ADS1299.

1> What is a role of Bias Amplifier?

Does it simply adds up or amplify or calculate the average of the value for each channel?

2>  Figure47 of the Data sheet, 1Mohm is between BIASOUT and BIASINV. How to be calculated and applied 1Mohm?

Thanks.

From_Hayden.LIM

  • 0
    TI__Mastermind 18285 points

    Hayden,

    I am moving your post to the correct forum. 

  • 0 in reply to Amy Schnoor
    TI__Guru 63196 points

    Hi Hayden,

    Thanks for your questions!

    The Bias amplifier is the ADS1299 is used to set the DC operating point of the patient relative to the system supplies. The selected channel outputs used to derive the BIASOUT voltage pass through a resistor averaging network and feed into the inverting input of the bias amplifier. The non-inverting input is held at mid-supply.

    The 1M ohm in the feedback path is in parallel with 1.5nF to give you a 106Hz cutoff, which is just wide enough to pass through 50Hz/60Hz noise. We drive the patient with an inverted common-mode to improve CMRR.

    Hope this helps!

    Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 70 points

    Hey Ryan,

    I'd like to bring the following forum thread to your attention: http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/268235.aspx?pi310983=1

    The contribution of community member Vojin Ilic is particularly noteworthy, as it seems to greatly improve CMRR as compared to the documented design that you describe above.

    In short: Instead of feeding back the RC filtered BIAS_OUT signal to BIAS_INV, the RC filtered BIAS_OUT signal is fed directly into the bias electrode. BIAS_INV stays unconnected in this design.

    I'd appreciate any comment from you as to why this apparently superior design with respect to CMRR is not adopted by Texas Instruments in the "official" ADS1299 documentation.

    Regards, RS

     

  • 0 in reply to Ryan Andrews
    Prodigy 10 points
    Hi,

    I have some problems with the driving of the CMRR. I would like to use tha ADS1299 as an EMG and thus hav to connect a RLD electrode.
    For the moment I connect this to the BIAS_OUT pin without anything extra. But it doesn't seem to function.

    For the moment I have not resistance and capacitance between BIAS_OUT and BIAS_INV because they didn't seem needed. Is this wrong?
    I'm using the internal BIAS_REF signal.

    Am i forgetting a connection or a setting in my code?

    Thank you very much