Hello,
I am having difficulty in setting an external VREF to the ADS129x (ADS1292). When I connect an external VREF of 240 mV (my signal is in the range of 0.1mV-1 mV, so trying to get a large gain by using a low VREF value), with unit gain, the ECG signal constantly drifts and gets stuck at certain arbitrary values every few seconds (the values are much lower than the 2^24 and arbitrary). The signal re-appears after few seconds.
With the above set-up, if I choose to user the internal voltage reference (say the setting for 2.4V), I get the same issue.
The external VREF is generated using an Opamp (OPA350). If this OPAMP is removed, the above system works well in getting ECG using the internal reference. Also, the acquisition is good if a voltage generator (desktop) is connected to VREFP to generate the 240 mV instead of the OPAMP.
Couple of questions:
-- Is it possible to use the internal voltage reference, if the VREFP is connected to 240mV and VREFN is GND ? In this case, what is the voltage reference range of the ADC ? (is it 2.4 V - 240mV ?). If so, why I get this drift and stuck up ?
-- Even if my VREF generated by the OPAMP is noisy, I am not sure why this pattern of drift-stuck-up-and recovery of ECG signal happens. Any ideas ?
I have baseline, notch filters etc in software and the drift-stuck-up seems unrelated to other noise sources.
thanks !