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Are there any filters on the ADS1298 eval board that are specifically for ECG?

Dave Babalu
Prodigy 105 points
Other Parts Discussed in Thread: ADS1298

Hi,

Are there any filters on the ADS1298 eval board that are designed to remove frequencies unnecessary for ECG so that only ECG-related frequencies are shown at the output? I mean, I know things like EMI are filtered out, but are other biopotential frequencies filtered out?

I guess another way to ask this question is what is the range of frequencies that can be easily accessed by this board? 

Thanks!

-David

  • 0
    TI__Mastermind 38745 points
    Hey David,

    From my understanding, biopotential signals are, for the most part, quite bandlimited. The ADS1298 is a device optimized for biopotential measurement, but it is important to understand all of the steps that change or could perhaps limit the bandwidth of the EVM board as a system. Let's think about it from input to output.

    First, the board inputs feature two stage RC low-pass filters. A quick calculation will show that the -3dB point for all of those filters is formed at 146.6 kHz, which is very wide bandwidth. The device itself features an integrated PGA that serves the dual purpose of providing a front end gain stage before conversion and band limiting input signals as a means of anit-aliasing. You can find the frequency specifications for the different gain settings in table 16 on page 56 of the datasheet.

    The delta sigma architecture uses oversampling as a means to improve accuracy and remove converter noise. The result is a digital filter response that is described starting at the bottom of page 50 of the datasheet but continues on to page 51. This filter's response depends directly on the device data rate that is configured in the registers for the device. In general, the filter has a zero (infinite attenuation) at the data rate and has a response of about -10 dB at f_DR/2 which is your effective Nyquist frequency. The device can convert data at up to 32 kSPS, though, so that will likely not be a limiting factor for any biopotential signals.

    In addition to the frequency response corresponding to the chip itself, the EVM software provides some tools to further process your results. On the ECG Display Tab, you will find options to pass raw data through either/any of the following filters: 50/60 Hz notch filter, low-pass filter, high-pass filter. Hopefully this explanation helps. Let us know if you have any more questions.

    Regards,
    Brian Pisani