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ads1293 ECG data readings

Nazrul Khan
Prodigy 230 points
Other Parts Discussed in Thread: ADS1293

Hello,

After configuring the ADS1293, I am reading the ECG data for the channels. All the received data represent 0 volt. Then I started to read the ERROR_STATUS/ERROR_RANGE1/ERROR_RANGE2   registers to see what is happening. Among other bits, DIF_HIGH_CH1/DIF_HIGH_CH2 are set. That means, INA output is out of range. According to the manual, the SDM will no longer sample the output of the INA, but instead will sample 0V. I believe, exactly that is what is happening. My question is, what is the remedy? How to overcome this problem? Any thoughts, please. Regards.

Nazrul

  • 0
    TI__Mastermind 49946 points
    Hi Nazrul,

    I am moving your post from Medical Forum to Precision Data Converters Forum where the ADS1293 device is supported.
  • 0 in reply to Praveen Aroul
    TI__Genius 16890 points
    Hi Nazrul,

    Check to make sure that your input is not too large. The maximum differential input is 400mV. Also make sure that you are within the input common mode range of the amplifier (0.95V < input < VDD-0.95V). If you have the RLD properly setup and are using it correctly the input common mode will be ok.

    Mike
  • 0 in reply to Michael Stout
    Prodigy 230 points
    Hello Mike,
    Thanks for the reply. My problem is the inputs. Seems, they are too high. By oscilloscope, I was measuring the voltage levels at the input. Even, without connecting the electrodes, the voltage level in those input lines are at 1.0 volt DC. Is it normal? Is that a common mode voltage? Also, with the electrodes connected, the ac swing is superimposed on that 1 volt dc. The ac swing peak to peak voltage is also about 1 volt. Are these voltage figures are normal at all? Your thoughts please. Regards.
    Nazrul
  • 0 in reply to Nazrul Khan
    TI__Genius 16890 points

    Hello Nazrul,

    There is no telling where the input can be at if the common mode is not used or not set up properly.  This is caused by leakage current in the input circuitry.  

    To set the common mode you use the RLD.  See figure 84 in the datasheet. 

    The 1V input is too large.  The max allowed in 400mV.  When you are using electrodes on a person the signal is very small, in the single digit mV range.  This small signal will be superimposed on the common mode set by the RLD.  The 1V swing is probably caused by bad grounding of the scope probe.

    Mike