ADS1299EEGFE-PDK: Single ended channels with feedback bias drive and reference electrode

Hi Karam,

SRB1 connects to all inverting (N) channels, whereas SRB2 can be individually connected to each inverting (N) channel. Since you have SRB1 connected to all channels, you should be fine without using SRB2. Alternatively, you could disable the SRB1 connection and connect SRB2 for channels 1,2,3, & 5. 

The bias driver bits are used to control the bias amplifier, there are several block diagrams in the datasheet, such as figure 33, that show how the voltage is routed. 

Additionally please see the BIOFAQ for more information. In ECG, the BIAS is known as RLD (right leg drive): https://e2e.ti.com/support/data-converters/f/73/p/772058/2855202

Hello, Alex

Thanks for your reply, the SRB bits are very clear now.

i will connect AIN0 and that will be my reference electrode correct?

and JP8 has a jumper across 1-2

Further, yes, i understand the DRL principle but in the datasheet there is a BIAS_ELEC and a BIAS_DRV, if i choose the BIAS_DRV option which is a signal generated by the ADS1299 chip. The below image suggests to set the internal bias drive reference but in figure 39, BIASREF signal source is shown to be fed externally?.

And per the datasheet if the configuration is Bias drive loop then the input channels will be biased and i will not need the JP25 pins anymore correct?

Hello, Alex

Thanks for your reply, the SRB bits are very clear now.

i will connect AIN0 and that will be my reference electrode correct?

and JP8 has a jumper across 1-2

Further, yes, i understand the DRL principle but in the datasheet there is a BIAS_ELEC and a BIAS_DRV, if i choose the BIAS_DRV option which is a signal generated by the ADS1299 chip. The below image suggests to set the internal bias drive reference but in figure 39, BIASREF signal source is shown to be fed externally?.

And per the datasheet if the configuration is Bias drive loop then the input channels will be biased and i will not need the JP25 pins anymore correct?

Hello, after putting a jumper between pin 5-6 on JP25 and setting the SRB1 bit to route all negative input of the channels i need to connect my reference electrode to SRB1 as you mentioned, is that AIN0 on the datasheet and the board ?

Hi Karam,

That is actually AIN1, you can see it on pg 51 of the user's guide to the left, and it routes to all of the positive channels, whereas SRB1 routes to all negative channels. You can use this for your reference, but then you will want to route all of the other electrodes to the negative channels for 1,2,3 & 5 instead of the positive. 

In terms of schematic, would recommend connecting your BIAS electrode to BIAS_DRV, not BIAS_ELEC. Please see page 50 of the user's guide for reference. 

Hello Alex,

I have been straight debugging for 2 days, i know this should be simpler due to the extensive support and well-explained datasheet you and TI provide respectively,

However, i haven't been able to get the desired result yet.

I want to configure 4 single ended channel with a reference electrode and a bias drive/electrode without using any external circuitry just the board and the electrodes, if it is possible could you elaborate how ?

and i am sure this could be very helpful for other people looking through the posts.

i really appreciate the effort

many thanks

Karam Jaber E.E

Hi Karam,

Let's try starting small from the BIOFAQ: https://e2e.ti.com/support/data-converters/f/73/p/775288/2868597#2868597

Can you make it through all of the steps including reading from a known signal source? 

Dear alex,

Yes. everything on the board works fine, all i need from you is some steps to setup  ANY configuration appropriate for EEG acquisition.

i have read the datasheet so many times i know it by page.

i have read the BIOFAQ over and over and still no luck.

i tried different combinations for the different pins, different electrodes, different jumper settings.

and i just checked the board right now and waiting for your reply asap.

I have formally contacted TI personnel to help me, however they said they are not familiar with the product and they re-directed me to someone else which kept on happening until now. Which means there was no help over the phone lines.

thanks for your understanding

Hello,

I have attached pictures to make it very clear that everything on the board is indeed working,

i have a function generator generating a sin wave at  hz 9 hz 22 hz connected to passive electrodes and the electrodes output to ADS1299EEG board  and with the appropriate attenuation from a multi-stage voltage division between two resistors removing the DC-offset with a capacitor.

Please refer to my previous reply, what i need is simple steps to set up my electrode connections for appropriate EEG signal acquisition