ADS1299: Difference in BIAS configuration of OpenBCI and ADS1299 schematic

Swapniil Kanwar

Part Number: ADS1299

This is in continuation of the question asked in thread, as it is a similar doubt, Thread: https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/424183/ads1299-bias-setting

I understand that in some of boards BIAS_INV is left open for Daisy-chaining purpose. But suppose I do NOT want daisy chaining, the board has BIAS_INV left open so no BIAS feedback loop is formed to reduce the common mode rejection. As per the OpenBCI schematic, the circuit looks as follows:

I did a raw experiment by shorting the electrode In8P with bias electrode in above diagram, putting In8N to 0V (gnd), and with a jumper-> connecting Bias_inv pin to the other side of 1Meg resistor attached at BIASOUT so as to form the loop. But I see no change in the values of ADC on shorting or by attaching any other value of resistor.

over 3 years ago

0 Praveen Aroul over 3 years ago

TI__Mastermind 49786 points

Hello Swapnil,

Due to the Thanksgiving holidays in the US, our response is delayed. We shall get back to you by next week.

0 TCT over 3 years ago in reply to Praveen Aroul

TI__Genius 11550 points

Hi Swapniil,

For daisy-chain application, the BIASINV pin will serve as the summing junction of the bias amplifier. The bias amp can be configured as Figure 38 in the datasheet for normal operation if the daisy chain is not used.

Please see the app note (see link below) on the RLD for the ECG application, which explains some of the RLD drive concepts for the ECG application. The BIAS amplifier concept is the same for the EEG application.

Does TI have an application note that covers how to improve common-mode rejection (remove 50/60Hz noise) using the right-leg drive amplifier (RLD)?

How do I calculate the DC gain of the RLD or BIAS amplifier?

Thanks

-TC

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ADS1299: Difference in BIAS configuration of OpenBCI and ADS1299 schematic