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Why the inputs of AD8236 need to be pulled to VDD and VCC in application of ECG measurement

Hi everyone,

Now I made a circuit to measure ECG based on the AD8236. I followed the example in the AD8236 manual as shown below.

But when I test with electrodes connected to the human body, I found the output of AD8236 remained 2.5v. I cannot see the ECG waveform at the output of AD8236. When I removed the pull resistors at the inputs of AD8236, I can see the ECG signal at the output of AD8236 by the oscilloscope. Does that normal? Did I make any mistakes? Appreciate your help.

  • Hi,

    Let me get back to you on this. In the meantime, could you elaborate the electrodes that you're using? My initial suspicion would be that the electrodes that you're using has some sort of capacitance. This capacitance together with the 953k at the inputs forms a high-pass filter that could attenuate the signal of the electrodes. You could try lowering the values of the two 953k resistors and see if that helps.

    A brief description about the input frequency range, and the electrodes specification would be helpful.