ADS1198ECGFE-PDK: Elimination of 50Hz noise

Prodigy 30 points

Replies: 4

Views: 71

Part Number: ADS1198ECGFE-PDK

Hi,

I recently purchased the ADS1198ECG-FE EVM for prototyping.

Although the board has RLD, ELEC SHIELD, I couldn't find clear instructions on how to eliminate the noise from 50Hz mains. This is greatly affecting the prototyping process.

In our current setup, we are using 5 electrodes where one of them connected to the AGND of the board as a gnd and the rest are used as channel inputs.

I appreciate your assistance on this,

Thanks

4 Replies

  • Hi Saba,

    Instead of having 1 electrode connected to AGND, connect this electrode to RLD. This will drive the inverted noise onto the body, canceling the 50Hz main noise. 

    Please see the BIOFAQ link in my signature below. There are several links that will help including a document explaining the theory behind common-mode rejection using RLD. 

    Best regards,

    Alex Smith
    Applications Engineer | Precision Delta-Sigma Converters

    Check out our helpful resources: BIO-FAQ: Common Questions for TI's ADS129x Family of Bio-Potential ADCs

    TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

  • In reply to Alexander Smith:

    Hi Alex,

    Thank you for your response.

    I went through the documents you sent earlier. However I am still not sure how to implement RLD in the EVM. I tried the following:

    1. Used the DB-15 EKG connector recommended for the EVM and attached RA, LA , LL along with RL so that I can observe Ch2, Ch3.

    2. Verified that the Channel Input is set to the Normal Electrode mode for Ch2, Ch3 

    3.Enabled the RLD Buffer (RLD Buffer Power = Enable) and the internal RLD reference (RLDREF Signal Source) in In CONFIG3 control register 

    4.Selected the electrodes for the RLD loop from the Right Leg Drive Derivation Control Registers controls
    (LOFF and RLD tab) - RLDP2, RLDP3, RLDN2, RLDN3  

    And still I am getting the 50Hz noise as you can see from the FFT attached.

    AM I missing something?

  • In reply to Saba Eas:

    Hi Saba,

    You can set normal electrode for all channels, enabling the RLD buffer and RLD reference is correct. 

    For your connections,

    Ch2 = RA - LL, Ch3 = RA - LA?

    I would like to confirm that you no longer have the 5th electrode connected to AGND? This essentially takes the noise that couples onto the body from the lights and directly injects it into the circuit GND.

    Let's confirm that the RLD is working. When you measure across R38, do you see a voltage near mid-supply? 

    If you set the RLD voltage to mid-supply instead of deriving from the input electrodes do you see mid-supply? 

    Best regards,

    Alex Smith
    Applications Engineer | Precision Delta-Sigma Converters

    Check out our helpful resources: BIO-FAQ: Common Questions for TI's ADS129x Family of Bio-Potential ADCs

    TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

  • In reply to Alexander Smith:

    Hi Alex,

    For my connections Ch2 = LA-RA and Ch3 = LL-RA according to the lead derivation.

    You are correct. I am using LA, RA ,LL and RL only. 

    I noticed that in the schematic of EVM (page 53 of ADS1198ECG-FE Datasheet) for some reason the bandwidth of the RLD loop was set to 46Hz. I haven't replaced the components yet. Do you believe increasing the bandwidth would solve this issue?

    I will test the mid-supply once I am at the office. 

    Thanks,

    Saba