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.
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 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,
