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ADS1299 in single-ended mode

Zhong Yincheng
Prodigy 50 points

Dear all,

  I have buy an EEG Front-End Performance Demonstration Kit and want to use it in an EEG system.  I use the evaluation software developed by TI to control the Demonstration Kit. I want to use it in an single-ended mode.

I have configured the jumper as the user guide described.

And I set the SRB1 to closed.

I connect the reference electrode to the JP25-4 which should be bias_elec.

And I collect the signal, but the 50HZ noise is very big which is above 3mv.

But when I set the SRB1 to open which will make it work in a differential-ended mode. And connect the reference electrode to the IN1N. And the 50HZ noise is about 10uv the signal is very good.

My question is where am I wrong ? Why it can't work in a single-ended mode, but can work in a differential mode?

Thanks,

Yincheng

  • 0
    TI__Mastermind 38745 points
    Yincheng,

    Do you also connect the reference electrode to JP25 pin 6 in addition to pin 4? If not the SRB input will be floating.

    Brian
  • 0 in reply to Brian Pisani
    Prodigy 50 points

    Thank you for your reply.

    I have connect it. And when I test the Noise with Common Reference on Negative Inputs as the user manual describe. it is about 1uv. 

    Our electrode line is about 30 cm long without shield. Could this be the reason why the noise is big in single-ended mode? But it work well in differential mode.

    Yincheng

  • 0 in reply to Zhong Yincheng
    TI__Mastermind 38745 points
    Hey Yincheng,

    To be clear, the 1 uV noise performance is when you connect the electrodes in differential mode? Or is that in single ended mode with the connection I proposed in my last post?

    Brian
  • 0 in reply to Brian Pisani
    Prodigy 50 points

    It is in the single ended mode to measure the system noise. As it described in user manual page 46, section 8.3. I think this can prove the single-ended mode is working. 

    And then I connect the JP25-4 and IN1P to the electrodes on people, noise is very big. JP25 5-6 is connected.

    Then I set the SRB1 to open, and connect the  IN1P and IN1N to the same electrodes on people. noise is very small.

    Yincheng 

  • 0 in reply to Zhong Yincheng
    TI__Mastermind 38745 points
    Hey Yincheng,

    The EVM is not supposed to be connected to human patients since it is not cleared by any regulatory agencies. It is to be used only in a laboratory environment with a simulator. In general, utility frequency interference does tend to couple quite a bit on to electrodes in biopotential measurement systems. A lot of developers will use a notch digital filter to eliminate that frequency. However, even that seems quite large. When you measure the noise, are you shorting the electrode inputs on the board?

    Brian