ADS1293: ADS1293 RLD and Common MOde

Hi,

RLD is important to bias/bring the body to a common mode voltage that could reside within the Amplifier and ADC working range, i.e. not at a floating/unknown voltage/potential that could be outside the Amplifier and/or ADC working range.

And, RLD also helps to suppress the common mode noises, such as 50/60Hz and other noises/interferences from environments and other surrounding equipment as human body and cables/wires act like antenna to pick up noises/interferences.

It's not hard to create another electrode/node for RLD placement, it's not very necessary has to be at the right leg, somewhere on the right side of the body away from the RA electrode may work.

For further details/discussions, you may do some Right Leg Driver research online and take a look at other threads -

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/842529/faq-does-ti-have-an-application-note-that-covers-how-to-improve-common-mode-rejection-remove-50-60hz-noise-using-the-right-leg-drive-amplifier-rld/3115361#3115361

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1134878/ads1298ecgfe-pdk-differential-pair

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1124203/ads1198-how-to-work-with-rld

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1096030/ads1293-voltage-on-1298-or-1293

You may also take a look TI's Patient Monitoring Training Videos -

https://training.ti.com/patient-monitoring?context=1148465

https://training.ti.com/patient-monitoring

https://training.ti.com/how-measure-ecg-guide-signals-system-blocks-and-solutions?context=1128637

Hi ChienChun,

Thanks for the quick answer. After going through the videos and posts, I understand much better the system. However I havent solve my question but maybe now I can explain better what I need:

Due to the size of my device, I can only use RA, LA, LL but I dont have space to RLD. So my question is how to I set up the ADS1293 so I can measure 3 Leads without RLD, making sure that the measurements are within the range of the device.

Big thanks

Hi,

Couple approaches you can try&test. And, yes, please make sure to test and do data analysis before final decision.

1. Do not use RLD. TI never recommends.

2. Connect the RLD output to all the input electrodes or pins to achieve pseudo LEAD BIAS instead of the body bias.

3. RLD electrode/pad could just be several centimeter away from any other electrode and with very good contact, then it could help improve the results

Do you happen to have/use an evaluation kit/board(EVM)?  It's suggested to test with the EVM to collect data for data analysis.

Please take a look of the EVM user guide to see how the RLD peripheral circuit is designed.

Thanks

Big thanks for the answer.

Yes, I am using the EVM as well. But the user guide doesnt give any information how to use it without the RLD.... Is there any information I am missing?

When you say: 2. Connect the RLD output to all the input electrodes or pins to achieve pseudo LEAD BIAS instead of the body bias.

Do you mean internally or do I need to modify the hardware?

Also, w

what should I do with RLDINV? Should it be connected to RLDOUT as in the schematics and then have that connected to IN1, IN2 and IN3 as you recommended ? Big thanks

Hi,

The user guide is using the RLD, but it's just a bit confusing as it doesn't use RLDOUT pin directly, instead, as you see the output of the RLD amp inside the block diagram, it is routed/muxed by the SELRLD and goes to IN4 pin and then connect to the RL electrode on body. So, it uses RLD but not the RLDOUT pin to connect to body.

Yes, as mentioned, TI never suggests not use RLD/RL electrode, so user guide doesn't not suggest that.

2. Connect the RLD output to all the input electrodes or pins to achieve pseudo LEAD BIAS instead of the body bias.

So, if refer to the block diagram you are showing, if RLDOUT is muxed/routed to the IN4 pin, then you can either connect that IN4 pin to IN3 and/or IN2 and/or IN1.

If SELRLD does not mux/select to route the RLDOUT to IN4, then you can connect the RLDOUT pin to IN3 and/or IN2 and/or IN1. 

"what should I do with RLDINV? Should it be connected to RLDOUT as in the schematics"

Yes, for starter, please start with the reference design in the user guide.

It's suggested to start with what are default suggested in the user guide and EVM to collect data(to get nice reasonable ECG data as reference/baseline first), understand, data analysis, and then modify little-by-little, one-by-one then collect data, data analysis, compare before the next modify.

Thanks

Hi,

I will try that and see how it goes. Big thanks for the help.

Thanks.