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ADS1292ECG-FE: ECG signal quality : user guide VS reality

jackofhearts
Prodigy 40 points
Part Number: ADS1292ECG-FE
Other Parts Discussed in Thread: ADS1292

Hi,

I am working on a ADS1292ECG-FE and I am trying to increase the quality of the ECG measurements. The measuring chain is as follows :

The resistors and capacitors have been choosen with high tolerance to minimize electrodes mismatch. I am using the RLD electrode.

I am working on a laptop with Windows XP, it is running on battery and it is far from the 50 Hz, so there should not be any problem regarding the 50 Hz noise.

I am using wet electrodes.

Here are my raw measurements :

Is it normal to get this level of ECG quality ? I find it to be bad, but I do not know if it is the supposed behavior. In the user guide of the ADS1292ECG-FE, the ECG which are displayed (pages 21, 23 and 25) are really good, and it seems like there is no filtering applied. 

I know I will certainly have to filter the signals to get better results but I was expecting the raw data to be better, simple low-pass filter still do not give great results, as you can see here :

Thank you for your support.

  • 0
    TI__Genius 11550 points

    Hi,

    Thank you for your post!

    In ECG applications, there are multiple ways power-line noise can inject into the system. It is still possible for power-line noise to couple into the system through the patient's body (ambient lighting), the ECG cables, and the board's surface, even for battery-powered ECG applications. It sounds like you are already using the RLD circuitry and good component tolerance for the input filtering to improve the CMRR performance and hence the power-line noise performance.

    The ECG plots shown in the ADS1292ECG-FE User's Guide are tested with a battery-powered ECG patient simulator either with or without any white noise injection.   

    From your raw measurements plot, the noise is about 50 uVpp before digital filtering. You can verify your system noise by shorting the input and measure the output noise performance. Table 1-8 in the ADS1292 datasheet show the expected noise performance for different device conditions (Output Data Rate, PGA Gain, Analog Supply, and Reference voltage). You can use them to compare to your tests.  

    Thanks.

    -TC