Bias Pinout

Is the bias upper pin connected to the BIAS_INV and the bias lower pin connected to BIAS_DRV or the other way?
https://github.com/OpenBCI/V3_Hardware_Design_Files/blob/master/OpenBCI Cyton Designs/OBCI_V3_32bit-Schematic.jpg

Comments

  • wjcroftwjcroft Mount Shasta, CA

    No. Both Bias pins are the final 'Bias' / Ground connection.

  • So there is no difference between the upper and lower Bias pins?

  • wjcroftwjcroft Mount Shasta, CA

    Correct.

  • In Bias_DRV there's a something called RS IM, what is RS IM?
    I see how Bias_DRV connects to the BIAS pins on the cyton, but I don't see Bias_Inv used anywhere, is it necessary?

  • wjcroftwjcroft Mount Shasta, CA

    @bci_sigcraft, I merged your new thread into this existing one.

  • wjcroftwjcroft Mount Shasta, CA

    Please consult the TI ADS1299 for external Bias circuitry recommendations.

    On the schematic, BIAS_DRV goes through an RC network, I assume for RF filtering purposes. The two components are R5, a 1 meg resistor, and C16, a 1 nanofarad cap.

    If you actually look at the TI data sheet, you can see that BIAS_INV connects all the ADS1299 chips as a BIAS_INV bus. So that all chips cooperate in estimating the common mode noise and derived inverse injection anti-mains voltage.

    Other RC pre-filter components are connected on each channel input pin.

    https://openbci.com/forum/index.php?p=/discussion/154/front-end-filtering-esd-cmrr-rfi

  • Hi,
    I don't mean in the Bias_INV in the ADS, I mean in the Cyton Schematic I don't see it being connected to anything. Does the Cyton not use Bias_INV?

  • wjcroftwjcroft Mount Shasta, CA

    Compare the Cyton and Daisy schematics. BIAS_INV on both boards are connected, and connected to both ADS1299s.

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