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ADS1292R: Respiration rate is highly sensitive to body motion and why current consumption is different when sensor is on-body and off-body, which respiration rate mode is enable

Hoang Nhu
Prodigy 20 points
Part Number: ADS1292R

Tool/software:

Hi ,


We are designing/testing our wearable ECG/HR/RR sensor patch using TI ADS1292R , and we found that respiration rate (RR) is highly motion sensitive : normally RR is in the 12-20 bpm range (breathes per minute). . But this (left-side) chest-worn sensor patch can give RR reading that immediately jumps from this normal range to 30-40 bpm if we move our arms briefly, suddenly.


Note that HR Heart rate reading doesn’t have this motion sensitivity issue (HR is quite stable, and isn’t affected much by motion). Is ADS1292R RR design prone to this type of (large variation ) issue due to motion sensitivity ? Is there a fix for this and/or any app note that discusses filtering/averaging technique to reduce the effect of motion on RR ?

A 2nd question also related to RR is the following :
- When RR mode is disabled, current consumption by the chip is not affected by whether the sensor patch is off body or chest-worn.

- When RR measurement mode is enabled (this is configured via a register bit in the ADS1292R chip ) , then current drawn by the chip is quite a bit lower (by 400uA) if the sensor patch is worn on the chest (on-body) via 2 electrodes & adhesives (to make contact with the skin on the chest ) VS when the sensor patch is not on the chest (off body): 

1408uA (when off-body) vs 983uA (on-body)

Are you aware of such Current-Consumption behavior of the ADS1292R as a function of whether RR is ON/OFF & electrodes off-body/on-body? Is it a known characteristic of RR design in ADS1292R ? Or it is a pcb board or setting error in our design ??

  • 0
    TI__Guru 62196 points

    Hello Hoang,

    Thank you for your post.

    Respiration can certainly be affected by motion artifacts due to the nature of measuring such minute changes in thoracic impedance. The solutions generally boil down to minimizing skin-electrode contact impedance and software algorithms with carefully designed bandpass filters to smooth out motion artifacts. Unfortunately, this is not something we have enough expertise in to offer much guidance.

    I have not observed such correlation between floating electrode inputs and current consumption of the ADS1292R. This could be caused by introducing a high-impedance (i.e. open-circuit) in the path of either the respiration modulation signal (RESP_MODP/N), the input lead-off current sources (internal pull-up/down resistors or current sources), or the RLD amplifier output driving towards the supply rail.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 20 points

    Thank you for your input on this matter. Although it doesn't directly address our current challenge, I appreciate your insights and the time you've taken to respond.