ADS1291: Using different AFEs for PPG and ECG aquisition

Anurag Kumar

Prodigy 70 points

Part Number: ADS1291
Other Parts Discussed in Thread: AFE4403, AFE4950, AFE4404, ADS1292

Hi,

I am wondering if it is possible to use different AFEs for ECG and PPG.

Like ADS1291 for ECG

and AFE4403 for PPG

Also how can we get synchronised data? Like ECG and PPG at the same time?

Will there be any sync issues?

Regards,

Anurag

over 3 years ago

0 Praveen Aroul over 3 years ago

TI__Mastermind 49746 points

Hello Anurag,

Thanks for your query.

Have you looked at TI's Bio-sensing AFEs where you have both ECG and PPG signal chain in the same device?

https://www.ti.com/data-converters/integrated-special-function/medical-afes/biosensing-afes/products.html#p1241=Electrocardiography%20(ECG)%20+%20Photoplethysmography%20(PPG)

We recommend AFE4950 for your application.

0 Anurag Kumar over 3 years ago in reply to Praveen Aroul

Prodigy 70 points

Hi Praveen,

I know there are combined sensors for PPG and ECG.

But, our use case needs them to be separate? So, can you please suggest me if it's possible to get both data from separate AFEs and in a synchronised manner?

Regards,

Anurag

0 Praveen Aroul over 3 years ago in reply to Anurag Kumar

TI__Mastermind 49746 points

Hi Anurag,

Yes, it is feasible to get synchronized ECG and PPG data from ADS1291 and AFE4404. I will get back it you on the synchronization scheme tomorrow.

0 Anurag Kumar over 3 years ago in reply to Praveen Aroul

Prodigy 70 points

Hi Praveen,

Sure, will be looking forwar to it.

0 TCT over 3 years ago in reply to Anurag Kumar

TI__Genius 11550 points

Hi Anurag,

Please see the document below, which describes the scheme to synchronize the ECG and PPG data from ADS1291 and AFE4404.

AFE4404 and ADS1292 Synchronization.pdf

Thanks

-TC

0 Anurag Kumar over 3 years ago in reply to TCT

Prodigy 70 points

Hi TC,

Thanks a lot for your input, it makes things much clear.

Also, I have few doubts, let me know if my understanding is correct:

Are we using CLK/2 for ADS1292, so that we can execute AFE4404 ISR early and then use flag clear to execute ADS1292 ISR. If yes, then can we also use CLK/2 for AFE4404 and vice-versa or Is it recommended to read PPG first?
What are possible ways to reduce CLK to half before feeding into ADS1292?
How GPIO1 pin should be configured?
If my Controller supports multiple SPI channels, can I use RTOS to manage them parrallely?

Regards,

Anurag

0 TCT over 3 years ago in reply to Anurag Kumar

TI__Genius 11550 points

Hi Anurag,

Please see my comments below.

The scheme is to operate AFE4404 at 4.096 MHz and 2.048 MHz clock for ADS1292 and hence the CLK/2. There is no requirement which data need to be read first. The ADC_RDY (AFE4404) and DRDYB (ADS1292) signals indicate the PPG and ECG data are ready for retrieval.
The clock divider can be implemented with a Divide-by-2 counter using a D-type Flip-Flop.
The GPIO1 signal is used to reset the START signal to the ADS1292. Keeping the GPIO1 low will reset the START signal and disable the ADS1292 data conversion and DRDY signal. You can use the GPIO1 signal as a resynchronize signal or to stop the ADS1292 ADC conversion.
I am not familiar with the implementation of the RTOS and the requirement for the parallel application. Any ISR read on the SPI bus must be completed within 2ms, as shown in the diagram.

Thanks

-TC

0 Anurag Kumar over 3 years ago in reply to TCT

Prodigy 70 points

Hi TC,

Thanks a lot for clarification.

0 TCT over 3 years ago in reply to Anurag Kumar

TI__Genius 11550 points

Hi Anurag,

Please do not hesitate to let me know if you need further assistance. Thanks.

Thanks

-TC

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ADS1291: Using different AFEs for PPG and ECG aquisition