ADS1299: Single - Ended Measurement

Part Number: ADS1299

Hello,

I have a customer that is asking if they can make a single-ended measurement of electrode impedance when SRB1/ SRB2 is connected internally within chip to the positive/ negative and electrode is connected to GND/ bias voltage. Would this work?

Thanks,

John

  • Hi John,

    Thanks for the post.

    The DC or AC leadoff circuitry should still be working the same with the internal SRB1 and SRB2 connection. They can verify it by turning on the DC leadoff circuitry and measuring the intended electrode's leadoff current.

    Thanks

    -TC

  • Hi TC,

    Sorry for the delay, I finally heard back from my customer. Their response in blue:

    The ADS1299, in default, measuring the voltage per channel differentially (IN1N-IN1P). While performing a lead off test - we flow current (6uA) only through the negative port (IN1N) where there is the real EEG electrode that is connected and perform a reading. The question is: What is the right way to configure the ADS1299 so that the measurement will be in single-ended mode, only for IN1N? Do we need to use BIAS or SRB for single-ended measurements?

    Thanks, 

    John 

  • Hi John,

    Thanks for the support.

    From my understanding, the referential montage EEG application is a single-ended mode measurement where all the negative input of the PGA is connected internally through SRB1 or shorted externally (See datasheet Figure 73). The DC leadoff for the reference electrode is done through the BIAS_OUT electrode or any low impedance return path. 

    Thanks

    -TC

  • Hi TC,

    Thanks again for the quick response. I sent your response back to the customer and will close / respond when I hear back.

    John