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ADS1299-4: Pace Detection in Hardware

Alwyn DSouza
Intellectual 360 points
Part Number: ADS1299-4
Other Parts Discussed in Thread: ADS1299, ADS1298

I'm intending to use the ADS1299 for ECG application due of its better noise ratings.

Since is chip is more suited for EEG applications there are no ECG specific hardware features in it like WCT, Pace detection as expected.

However for hardware pace detection I found the document "Hardware Pace using Slope Detection". It shows a a ckt as under:

The standards though required pace detection to be measured on each Lead, so from the looks of it this circuit would be needed on all channels.

I have seen similar block diagram in the ADS1298 datasheet where both the pace buffers are fed from even and odd channels. To do this external to the ADS1299 would need quite a bit of circuitry.

Am I inferring this correctly?

Also I see that after reading another post regarding pace detection a user had written that the pace amplitude being detected was very low, so there is probably scope for improvement in the above circuit.

Of course to get over all this one can use the ADS1298 and it has internal pace buffers but I would like to use the ADS1299, and implement the WCT and Pace detection in external hardware.

I'd like to hear from the experts here if there is any better way of doing this, especially from the point of reducing the chip count.

  • 0
    TI__Guru 66316 points

    Hello Alwyn,

    Yes, you would require some additional circuitry to implement the hardware pace detection circuit above with the ADS1299. Primarily, you will need some amplifiers to convert the differential input signal into a single-ended signal. You will have to connect the DIFF-to-SE stage before the PGA inputs (i.e. outside the ADS1299 device), which may require additional gain. This is different from how the ADS1298 implements this feature because the differential input is first gained by the PGA, then converted to single-ended before it is output on one of the two PACE_OUT pins.

    The WCT amplifiers would need to be added as well, one for each of the three primary electrodes. 

    So, while this all can certainly be done discretely, and there are some experts who have done it well, my suggestion would be to first decided whether the improvement in ADC noise performance is really worth it to give up the ADS1298 features.

    Best regards,