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ADS1298: Question about 0.05Hz high-pass filter for ADS1298

William Frost.
Prodigy 20 points
Part Number: ADS1298

Hi,

We are currently redesigning a resting ECG to use ADS1298. Since ADS1298 is a DC coupled frontend, we must implement a 0.05Hz -3dB highpass filter by software. Doing so by using an FIR filter will require too much memory and computational power for a small MCU like MKL16Z32VLH4 or similar. High-pass IIR filters are very tempting to use for their lower memory usage and computational power requirements. However, they have the non-linear phase response downside.

I have implemented the attached filter in C and it works exactly as expected. 

I have a few questions about this.

Is it fine to use this kind of filters (like the one shown in the attached images) for resting ECG?

What features of the ECG signal might be affected by these non-linearities on the phase?.

Can you recommend some alternative solution for a 0.05Hz high-pass filter?

I have read about compensating the IIR phase response by using an all-pass filter in cascade, but so far I have not found a way to design such a filter.

I will appreciate any comments, suggestions, links, that might help me with this problem.

Thank you very much in advance,

William

  • 0
    TI__Guru 59726 points
    Hi William,

    Thank you for your post and welcome to our forum!

    The non-linear response should not affect the ECG signal at those low frequencies. It would be more of a concern if this non-linearity occurred within the ECG signal bandwidth of interest. In that case, the signal content would become rather distorted.

    Keep in mind that even simple R-C high-pass filters have a non-linear phase response as well. This input structure is used frequently in AC-coupled ECG applications that do not use a driven right-leg electrode to bias the patient.

    Best Regards,
  • 0 in reply to Ryan Andrews
    Prodigy 20 points
    Hi Ryan,

    Thank you very much for your fast reply. I was not usre wether the S-T segment slope would be affected in some way by this filter. I will keep this IIR filter and move on to the implementation of the software pacemaker detection.

    Best regards,
    William