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ADS1299 lead-off current calibration

Other Parts Discussed in Thread: ADS1299, AFE4300

Hello,

I'm trying to measure electrode impedances with ADS1299 lead-off detection circuit. I get decent results. In the datasheet it states that the current accuracy is +-20%. 

To get more accurate results I wonder if it is possible to calibrate the current output? Or does it really vary +- 20% each time I try measure?

  • Hey Sami,

    That number specifies accuracy across devices and channels. I do not expect the current source accuracy on one channel of one device to change significantly between tests. It will, however, shift over temperature.

    If you wanted to calibrate a current source at room temperature, you could inject the current across a resistor with a known value and measure the resulting voltage. Then divide the measured voltage by the known resistance to measure the current source magnitude for that channel.

    Realize, though, that dc lead-off method for impedance measurement is flawed in that it only provides resistance and no reactive impedance information . Even ac lead-off cannot do this since its impossible to retrieve phase information from the data output. If you are looking to make accurate measurements of impedance, you might want to look at the AFE4300.

    Regards,
    Brian Pisani