ADS1298ECGFE-PDK: How to calibrate ADS1298ECGFE-PDK/ ADS1298

Part Number: ADS1298ECGFE-PDK
Other Parts Discussed in Thread: ADS1298, ADS1298R

Hi,

We are using  ADS1298ECGFE-PDK to acquire ECG data. We are observing a 11mV offset in the recorded data of all the channel.

We tied the Channel 3P and Channel 3N of ADS1298ECGFE-PDK  to ground and recorded the values. We could observe a 11mv offset in the Channel 3 of ADS1298(since ADS1298 measures differential voltage i.e Channel 3P- Channel3N).

1.Is this a normal behaviour ?

2.How should we compensate for the offset in all the channels ?

3.Will a normal offset correction on the ADS1298 channel work ?

4. How should we calibrate the channels where RLD is used as the reference ? (since RLD is also generated by the ADS1298)

5. How should we calibrate the channels where WCT is used as the reference ? (Since WCT is derived from channel 3P,channel 3N and channel 2P).

6.Please guide us through the process of calibrating the ADS1298 for (Lead I,II, V1-V2-V3-V4-V5-V6 ECG system )

We are in plan for using the same calibration approach for our custom Board with ADS1298

We used ADS1298xECG-FE software from TI for visualising  the data from ADS1298ECGFE-PDK. 

  • Hi,

    For questions 1, 2 and 3, unless your signal source(e.g. ECG simulator) created some offset; otherwise, please refer to ADS1298R user guide page 31 -

    "

    NOTE: For display that shows 6 leads combined, the ECG signals have any DC offset removed and
    a different offset added to the signal to display the signals as shown. To see the raw ECG
    data, you can select the individual signals as described below in the Zoom feature (box 4).
    2 - ECG Separation Feature
    The ECG separation control toggles the vertical distance between the input plots. This capability is
    useful when ECG signals are large and require more separation to avoid overlap, or to collapse the
    range between signals when the ECG signals are small.

    "

    Would you please clarify what you mean by "Calibration"?  or Do you actually mean "Configuration"?

    There are several registers and values customer need to configure to achieve each function/feature of the ADS1298.

    ADS1298 the IC, itself doesn't require any calibration, but the final product itself might need.

    For questions 4,5 and 6,  It's suggested that customer do it step by step, e.g. try to achieve question 4 first.

    Please refer to datasheet 9.3.1.7.6 Right Leg Drive (RLD) DC Bias Circuit and Figure 43 to decide how many RLDxP and RLDxN switches user want to close to send the differential input to the Non-inverting input of the RLD Amp; there is not a definite nor exact way for this. Customer will need to test, observe and analyze the results/outputs with respect to different configurations before making the final decisions.

    Similar procedures and concepts apply to the questions 5, please refer to datasheet 9.3.1.7.3 Wilson Central Terminal (WCT) and Chest Leads and do similar test, observe and analyze the results/outputs with respect to different configurations before making the final decisions.

    Highly suggest to note down/record the relevant registers settings before doing each experiment and note down every change made, so that the results can be tracked back to the corresponding registers and parameters settings.

    "We are in plan for using the same calibration approach for our custom Board with ADS1298"

    Yes, it could be a good starting point/seed/reference, but note, depends on the final product's design, and/of electrodes, etc, there might still be some configuration/calibration required through tests and analysis.

    Thanks

  • Hi ,

    Thanks for the reply.

    We are constantly observing 11mV offset when we pull ADS1298 Channel P and Channel N both to ground.

    Since the ADS1298 is use for measuring Bio potential ~ ECG which of 1-2mV in range . we are quite not sure how to eliminate it.

    Any help in this regard of calibrating the ADS1298 Measurement system will of great help.

    By calibration we mean to eliminate the offset of 11mV measured in ads1298 PDK

  • Hi,

    May I ask are you still using the ADS1298EVM and the GUI?

    When you say "We are constantly observing 11mV offset when we pull ADS1298 Channel P and Channel N both to ground.",

    May I ask which channel?  Could you try one channel for now?

    Would you please take and provide a picture or a drawing how you did above and a screenshot to show where you see the 11mV offset? did you see the offset in the ECG Display tab? or the Scope tab?

    As mentioned in the user guide -

    "For display that shows 6 leads combined, the ECG signals have any DC offset removed and a different offset added to the signal to display the signals as shown."

    Please see if you could follow the EVM user guide page 29 -

    4 ADS1x98ECG-FE Input Signals

    NOTE: Before evaluating specific ECG functions, it is recommended that the user acquire data with inputs shorted internally. This configuration ensures that the board is operating properly.

    4.1 Input Short Testing

    By default, the EVM powers up with the individual channels to an internal short with a data rate of 500SPS and a PGA gain of 6. Once the Acquire button is pressed, the Scope Analysis should reflect inputreferred VPP values less than 5µVPP

    4.2 Internal Test Signals Input

    Configuration Register 2 controls the signal amplitude and frequency of an internally-generated square wave test signal. The primary purpose of this test signal is to verify the functionality of the front-end MUX, the PGA, and the ADC. The test signals may be viewed on the ECG Display tab, as Figure 31 shows. Detailed instructions for using the ECG Display tab are provided in Section 3.5.4.

    Could you use the EVM GUI's Channel Registers tab, under Channel Input to set/configure such one channel to internal short? 001 = Input shorted (for offset or noise measurements).

    And also try internal test signals - 101 = Test signal

    Thanks,

  • Hi,
    Since I did not hear back from you, I believe my suggestions answered your questions.
    I will close this post and if you have any pending questions, feel free to post them here or open a new thread.
    Thanks and have a great day!