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ADS1293EVM: Measure 1 lead ecg with 2 electrodes

Rene Hermans
Prodigy 90 points
Part Number: ADS1293EVM
Other Parts Discussed in Thread: ADS1293

We have a ADS1293EVM board and looking how to configure it to measure only one lead ECG, so with only 2 electrodes.

We want to measure a proper ECG signal, so the morphology of the signal must be visible.

What is the best way to do this?

1) Use the answer as noted in: https://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/205432 

    a) why is the ac coupling necessary?, in the drawn ecg-frontend noted in paper 'analog signal chain considerations for medical applications' (from ti), there is a dc coupling?

2) Connect INA- to the GND and use this as reference on the body?

3) connect 10MOhm To GND from INA+, and connect 10MOhm to GND from INA-.

4) ? any other method.

Another question regarding the 1293EVM board:

During investigations we saw that the shield on connecter J1 of the ADS1293EVM board is not connected to the AGND as noted in the schematic. Why does the board differ from schematics, or are we doing something wrong?

Kind Regards,

Rene.

  • 0
    TI__Mastermind 38745 points

    Hello Rene,

    All of your questions are related so let me provide a single answer.

    The inputs of the ADS1293 must remain within the common-mode range of the front-end INA. This can be accomplished in 2 ways:

    • Bias the patient. This is typically done in many ECG systems using the "Right Leg" electrode. This electrode does not sense any ECG signals, it only applies a signal to the patient so make sure the patient is biased within the range of the ADC. There are also other benefits to using a "Right Leg" electrode. This can be performed on the ADS1293 by utilizing the RLD amplifier. This method has one major drawback: it requires an additional electrode.
    • AC couple the inputs. This allows only two electrodes to be used since the common-mode is determined by the biasing circuit.

    Generally you do not want to connect the RLD amplifier output to the INA- and the patient, because then the noise from the RLD amplifier will be seen by the ADC. If you apply the RLD to the patient in a separate electrode, the noise will be common to both inputs and will therefore be rejected since the inputs are differential.

    How were you able to determine the connection between AGND and the shield of the electrode? It should be connected since the schematic was used to generate the PCB.

    Brian