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RTOS/ADS1298: Lead off AC Mode Behavior

jameel magzal
Intellectual 810 points
Part Number: ADS1298

Tool/software: TI-RTOS

Hi,

We are using the ADS1298 lead off detection, using AC mode. we did this by writing to the lead off control register value 0xE1 and value 0xFF for both LOFF_SENSP and LOFF_SENSN, when we do this and monitor the input we see ~200 uv sine wave with no resistors attached to the input, is this a normal behavior? if so, how do I extract the real amplitude after adding resistance? as i observed when adding ~30 kohms, the amplitude falls inside the initial 200uv.

Regards,

Jameel 

  • 0
    TI__Guru 66186 points

    Hello Jameel,

    Thank you for your post!

    We will need to see a connection diagram showing where the 30k resistor is connected in your circuit. Can you please provide a schematic and the complete list of register settings?

    One detail that caught my attention is that you're using the smallest magnitude current source (6 nA). This will be the peak current of the AC lead-off excitation waveform. 6 nA x 30k = 180 uVp. This signal may be too small relative to the noise that you see in your circuit without the external resistor. Try using a larger resistor or current setting.

    We've recently released an article that discusses impedance measurements using the ADS1298 lead-off circuitry. Perhaps you'll find some of the information useful!

    How to accurately measure electrode impedance for lead-off detection in ECG systems

    Best regards,