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[ads1299] signal with much nosie.

qi wang
Intellectual 480 points
Other Parts Discussed in Thread: ADS1299

Hi ,

I am using ads1299 to measure ecg signal, but it seems that there is much nosie and interference.

1) power line interference is huge

2) when people walk around me, there is huge interference

3) when stretch the cable between the electrode and the board, there is huge interference

For the bias electrode, I used JP6 to get the voltage generated by a voltage divier on the board;

For the reference 'SRB1', it is directly from the body (JP8) and then given to all the negative inputs of each channel.

Why is it like this? Thanks!

Best,

Qi

  • 0
    Intellectual 480 points

    By the way, some other hints.

    I found the voltage of for biaselectrode(from voltage divier on board) is 0V. The reason should be that the circuit is powered by AVDD(2.5) and AVSS(-2.5), so the ouput is 0.  But can this kind of bias voltage work well to deal with common mode interference?

    Also tried bias drive function (using the closed loop in the circut), but the bias voltage is still 0V.

    Dont know if it works since bias voltage is 0V?

    Thanks.

  • 0 in reply to qi wang
    TI__Mastermind 38745 points
    Hey Qi,

    Noise and interference in biopotential systems is a challenge that many applications face. It may be comforting to know that your issue is likely not unique to your setup. I would say that given your setup, they best thing would be to digitally filter the data to eliminate the interfering signals.

    In regards to the bias voltage being 0V, you must remember that voltage is a relative quantity. We measure voltages "with respect to" another voltage. The "ground" potential on a circuit is simply the designated voltage with respect to which all other board voltages will be measured. The quantity "0" just indicates that it is at the same potential as the potential which is designated as ground in this particular circuit and does not indicate that something fishy is going on. Your intuition was correct: 0V = (AVDD+AVSS)/2 in this case.

    The voltage of the bias amplifier will be centered at 0V since the amplifier's reference voltage is at mid-supply, even in the closed loop. A better tool to study the behavior of the bias output is an oscilloscope so that you can see the amplifier attempting to correct for common mode signals (if the interference is truly common mode; in some cases it may not be).

    Regards,
    Brian Pisani