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ADAS1000 measurements without right leg drive problem

Question asked by Zrelieskim on Jul 21, 2014
Latest reply on Jul 23, 2014 by Padraic

Hi,

 

I have a problem concerning ECG front end ADAS1000. We have been evaluating this chip for quite some time now. Everything seems to be working fine except for one very annoying feature. We have been using an ECG simulator to verify the results.

ecg_good.pnggood ecg signal

 

The problem occurs when not using a right leg drive, to push back the common mode to the body. After extensive testing we have come to the conclusion that it is not neccesarily right leg drive problem since pushing the main potential to any fixed voltage seem to fix the problem. When not using this fixed potential the ecg signal seems to float away and starts oscillating around 50Hz and its harmonic. The oscillations are so bad that the ECG signal is lost completely.

 

ecg_bad.pngafter letting go rld

 

After connecting back the right leg drive signal (or ground or Vref or supply) the signal immediately goes back to normal ecg waveform.

 

The development board we are using is very similar to the official development board.

 

We have tested the same functionality on the Texas Instrument ADS1294 and there everything seem to be working fine.

 

So my question is as follows. Can the ADAS1000 be used without connecting the right leg drive signal and only use the differential inputs such as RA, LA and LL.

 

Thank you for your time.

 

P.S: the images are not from the ecg simulator to get more real results.

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