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ADS1299EEGFE-PDK: Re: Common mode noise rejection from measurements.

Sushant Rajbhar
Prodigy 90 points
Part Number: ADS1299EEGFE-PDK
Other Parts Discussed in Thread: ADS1299

Hello Team,

 I am doing the testing on ADS1299 EVM board with the following settings:

Type of supply: Unipolar

Type of signal measurement: single ended

Settings as follows:

Jumper settings as follow:
JP7: No jumper
JP25:1-2: No jumper, 2-3: No jumper 4-5: Jumper connected
J6: No Jumper

GUI settings are as follows:

 

We have used a separate board for the amplification of the input signal.

The differential signal from an EEG simulator is converted to single ended and then amplified by a factor of 100.

The board has a protection circuit, OP-AMP and instrumentation amplifier to do the necessary task.

The GND reference of the EEG simulator is connected to ref voltage (2.5V) on the EVK so as to provide a mid supply to the signal to be measured.

The ADS1299 EVK is powered ON through  a battery.

The EEG simulator is also powered ON through battery supply.

Moreover, during the measurements, the laptop on which the ADS front end is installed runs on battery supply.

The issue we are facing is:

When we try to measure the voltages, there is a common mode noise of 50Hz. I am unable to figure out from where the same is appreaing.

The cables used for connections is a shielded cable which eliminates the possibility of radiated noise.

The possibility of conducted noise is also very low since none of the devices are run on the mains supply.

Attached is the xls where we have recorded the data.

Can you please help us to get rid of this noise?

Also any further steps to improve the accuracy and noise performance would be appreciated.

Best Regards,

Sushant50Hz noise.xlsx

  • 0
    Prodigy 90 points

    In support for the reduction in common mode noise, please find the attached screenshots

    I have placed the following jumpers.

    J6 (35-36)

    JP25 (3-4) and (5-6)

    This will short the ADC input with the ref and bias.

    The SRB1 is closed in the application and the readings are taken for 500SPS, 5000Samples/channel keeping the gain 1.

    I could observe a noise of around 13uV during measurement.

    Possibly this noise must be interfering with the 10uV signal that is being given.

    How do I reduce this noise?

    I have mounted the extra decoupling capacitors on the ADS EVK.

    Kindly help me knowing whether the above signal must be overwriting the required signal or is there any other source of common mode noise that needs to be reduced?

    Best Regards,

    Sushant Rajbhar

  • 0 in reply to Sushant Rajbhar
    TI__Genius 11550 points

    Hi Sushant,

    Thank you for your post! We'll back to you this week.

    Thanks.

    -TC

  • 0 in reply to TCT
    Prodigy 90 points

    Hello TC,

     We have figured out the noise source.

    Seems that even if we not connect AC mains to the testing setup, the 50Hz noise from the nearby mains is coupled with the signal.

    This is not reduced even if I use the notch filter.

    Any suggestions to reduce the 50Hz noise?

    Sushant 

  • 0 in reply to Sushant Rajbhar
    TI__Genius 11550 points

    Hi Sushant,

    The ECG system commonly employed the use of the RLD scheme to improve the common-mode rejection and reduce the power line noise coupling into the system. I have attached the link below for the application note which show the detail of the implementation. 

    Improving Common-Mode Rejection Using the Right-Leg Drive Amplifier

    Thanks.

    -TC