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ADS1294R impedance respiration measurement

Felipe L
Prodigy 250 points
Other Parts Discussed in Thread: ADS1298R

Greetings,

Let me first congratulate you for this great IC (ADS1298R).

We are currently having some trouble with the respiration measurement. Our system is able to resolve down to a delta impedance of 3 Ohms with various levels of baseline impedance (500, 1000, 1500, 2000) Ohms, but when it comes to 1 Ohm delta impedance we come out just with noise (but the data sheet states the chip can do the job at least to 0.1 Ohm), so i guess i have some trouble with my setup.

The configuration is AVDD = 1.5V, AVSS = -1.5V, DVDD = 3.0 V. The design is based on the ADS1298R kit, but R96 and R97 have been changed to 18K to increase the injection current.

Any help or suggestion would be greatly appreciated.

Regards,

Felipe.

  • 0
    TI__Mastermind 43915 points

    Hi Felipe,

    Two areas I would look at are the RLD derivation and the caps used in the AC coupled input path. We put together a little information on the front end for respiration measurements located here -

    http://e2e.ti.com/support/data_converters/precision_data_converters/w/design_notes/ads129xr-respiration-design.aspx

    I know RLD derivation helps a lot with noise when it comes to ECG monitoring but I have not looked into it too much when it comes to respiration measurements. If you are using the RLD to bias the inputs post AC coupled path to bring the inputs within range, I imagine RLD derivation could help. I know on the EVM, we use the power supplies to bias the input and not the RLD for the respiration channel. You can give these app notes a read to see if they help at all.

    http://www.ti.com/lit/an/sbaa181/sbaa181.pdf

    http://www.ti.com/lit/an/sbaa188/sbaa188.pdf

    Regards,

    Tony Calabria