Hi Everybody,
I'm currently using 3 channels of the ADS1294 in combination with a 5-lead cable. All three channels are referenced to LL, this is, the negative channel inputs are connected with left leg electrode. The positive inputs of channel 1, 2 and 3 are connected to RA, LA and Cx. I've also a pace detection circuit which is connected to TESTN_PACE_OUT2 and feed with ch1 (RA).
I tried to realise a right leg loose detection with continuously monitors the state of the right leg electrode. Therefore, I added the square wave signal from GPIO3 to the right leg drive signal (with a 100k resistor in series, to avoid excessive patient currents). The signal should pass the input filters of all channels as soon as the RL electrode is connected to the patient. In order not to reduce CMRR by putting a detection circuit in front of the ASIC, I decided to use the TESTP_PACE_OUT1 (connected with LA electrode at ch2) as a source for the detection circuit.
This works pretty well as long as only RL, LL, LA and RA are used. As soon as I connect Cx, the voltage at the TESTP_PACE_OUT1 output does not drop if I remove RL electrode. I did a few tests and found out that not the cable or the layout is the problem. Then I deciced to use TESTN_PACE_OUT2 for both, pace and RL detection and it got much better, but still not satisfying.
Is there any dependence between the two pace outputs? Can you recommend any register setting which may help? Any other recommendations?
Thanks in advance!
Best regards,
Michael