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ADS1292R: Data converters forum

Part Number: ADS1292R

Dear TI experts:

Hi, I'm designing an wearable sensor for ECG detection.

I want to measure 2-electrode ECG and respiration without a third electrode.

I connected RLDOUT after the input ac-coupling capacitors with resistors to cancel common-mode voltage.

And, I placed RC filter on the channel input to reject common-mode voltage and high-frequency noise. 

1. I'm not sure this RLD buffer can cancel the common-mode voltage on both ECG and respiration channels.

2. I want to know how to decide the values of R3 and R4 resistors.

3. Are R2 and R6 necessary to protect patient? There is already R1 and R5. 

Here is my schematic:

If you have additional recommendations, please notice me.

Best regards,

  • Hello Yunsik,

    Thank you for your post.

    I recommend taking a look at the ADS1292RECG-FE User Guide and the Respiration section of the ADS1292R data sheet. A couple key differences I notice in your schematic include:

    1. The IN1P and IN1N inputs are not biased to a known DC voltage. After C15 and C26, a resistor divider can be used to establish a mid-supply common-mode. We recommend choosing values that that set the high-pass filter cutoff to > 50 Hz or 60 Hz. For example, 470pF series caps and resistor divider circuit with 10M per resistor.
    2. The 51k resistors should only be included in the ECG signal path and can cause a problem for respiration measurements. In Figure 56, an R-C low-pass filter should be used in the signal path to IN2P and IN2N only (not shown in the figure).
    3. R3 and R4 can be reduced to about 10M and C16 and C22 can be reduced to 0.1 uF. The high-pass filter cutoff is typically around 0.1Hz.

    Schematic Redrawn:


  • Hi, Ryan,

    I revised the circuit according to your recommendations.

    Here is my schematic:

    1. Because this device is battery operated, I don't care about 60 Hz noise. So, I set the high-pass filter cutoff to 10 Hz.

    2. In the datasheet, the low-pass filter already exist in front of the ADC. Is it necessary to put RC filter in the signal path to IN2P and IN2N? 

    3. In AC coupled applications, is the patient protect resistor really required? I want to save passive components.

    4. How to choose capacitance of C18 between 47 nF and 4.7 nF?

    Best regards,