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Hello! I need to implement a 3 channel ECG meter that uses 3 electrodes. Is it possible to do this with ADS1293? I tested the circuit with 4 electrodes, on ADS1293EVM, and it works good! But when I disconnect RL electrod ECG is very noisy. I also don`t find any information about 3 electrodes schematic in datasheet.
Also I'm found some links and test this solution (When RLDOUT connect to all channels through resistors 10M), but it doesnt work to.
ADS1292R starting questions - Data converters forum - Data converters - TI E2E support forums
ADS1293: Can I use the ADS1293 for a 3 channel EMG - Data converters forum - Data converters - TI E2E...
Hello Maksim,
Welcome to our forum and thank you for your post.
It sounds like you are using the three primary electrodes (RA, LA, and LL) for ECG measurement with a fourth electrode (RLD) for biasing the body. The quick answer to your question is that, by removing RLD, your input signals do not have a defined common-mode voltage.
Remember that the body's electrical signals are floating with respect to the ECG measurement system. Without establishing the common-mode voltage, the input signals can exist outside the usable range of the amplifiers inside the ADS1293. This can give poor results. Also, the RLD helps to reject the common-mode noise (i.e. power line noise) on the electrode inputs. Without RLD, you will need to AC-couple the electrode inputs.
Please review some of our overview material on ECG applications contained in this video training series:
Best Regards,
Hello Ryan,
I watched these videos, but did not find the answer to my question. Maybe there is a ready-made schematic solution that I could check.
Hello Maxim and Maksim,
You may use any of our ADS129x devices without the RLD electrode. The only change needed is the inputs must be AC-coupled instead of DC-coupled.
One way to do this is to use a resistor divider after the DC blocking capacitor in series with each electrode:
Another way is to use a single pull-up resistor to the output of the RLD amplifier:
Best Regards,