50Hz Noise in AD8233.

Hi,

we have designed a ECG monitoring product which uses AD8233 and AD7091R as a front-end. Our design is 0.034Hz to 159.9 Hz with a gain of 200 and 0.765 Q-factor. Everything works fine with few problems.

1) When the device is worn by a human and if he is touching a 50HZ supply line, the 50HZ noise is being picked up by the device. Is there a way to avoid this?

2) There is a small noise in the ECG. The contact is prepared well before the electrodes are placed. And a wet contact is maintained between body and the electrodes. Attachment shows the Noise. How to remove this randomly occurring noise?

3) When the person wearing the device breaths heavily the baseline keeps wandering. Any suggestion to remove the baseline wandering?

Attached signals are captured at Vout of AD8233 using Analog discovery kit, on a live human.

Thank you,

Bharath

attachments.zip
  • 0
    •  Analog Employees 
    on May 23, 2017 8:24 AM

    Hi,

    1) It is quite common to implement a 50Hz or 60Hz rejection filter (a notch filter) to remove the mains coupled interferences that may end up coupled when the interference is high (or the coupling is high as when the person is touching a 50Hz supply line).  Making the device battery powered or isolating it from the mains will help minimize the interference, matching the impedance of the two differential paths (IN+ and IN-) will also help minimize the potential Common mode to Differential mode conversion, although it is hard to control how well matched the contact impedances are. Using tight tolerance pullup resistors (if you are using pullup resistors for lead on/off detection) will help. Using threaded wires in a shielded cable also help minimize this. RLD (that I believe you are already using) also helps.

    2) It is hard to appreciate any noise without the raw data. It may also be 50/60Hz interference. Or it could be caused by some other portions of the system (mcu waking, some switching going on, RF link transmitting data, rectified RF interference...)

    3) It is also quite common in ECG solutions to implement a base line wander removal algorithm/filter. Low frequency content associated with respiration and subtle slow movements end up coupling due to the high pass filter which is set so low at 0.034Hz. Setting it up higher at 0.5Hz will get rid of the respiration artifacts but will distort the ECG slightly, specially in the ST segment interval.

     

    Rgds

     Roberto

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:48 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin