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ADS1292R: Design ECG and respiration sensor without RLD

kim yun sik
Prodigy 20 points
Part Number: ADS1292R

Dear TI experts:

Hi, I'm designing a 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.

Here is my schematic:

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

2. In the datasheet, the low-pass filter already exists 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,

  • 0
    TI__Guru 66296 points

    Hello Kim,

    Thank you for your post and welcome to our forum!

    1. Although your device is battery operated, power line noise at 50 Hz or 60 Hz can still couple onto the patient, the cables, or the circuit board itself. Therefore, it's still helpful to reject this noise as much as possible. In the respiration signal path, the low-frequency respiration waveform is modulated by the square wave carrier to higher frequencies. There is no reason to reduce the high-pass filter cutoff to 10 Hz, so I recommend increasing it to > 60 Hz.
    2. It is typical to add an additional low-pass antialiasing filter in the signal path. The cutoff frequency used will vary, but it typically around 10kHz.
    3. Patient protection is not a topic we can assist with. There are specific protection requirements for different medical equipment classes, some which require more protection than others.
    4. Use a 47-nF cap on Channel 1 (C18) for respiration measurements.

    Best regards,