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Setting problem of ADS1299 EEG-FE

Fanyi Liu
Prodigy 30 points
Other Parts Discussed in Thread: ADS1299

I'm using ADS1299 EVM.  I set all jumpers as shown. But i’m not getting a  correct signal.  Could anyone help to check this setup? Is there anything to be adjusted?

I'm using single-ended inputs. The input electrodes connect to the +pins of CH1 and CH2(pin32&36 of J6).

I'm kind of confused with the reference electrode and bias electrode. I have closed the SRB1 bit in software. Should i remove the jumper on pin1&2 of JP25 and have bias electrode connected to pin2?  And where should i have my reference eletrode connected? By connecting pin5&6 of JP25, REF & BIAS are connected together, does it mean i only need a bias electrode?


Another problem is  the 50hz-frequency interference. what shoud i do on the board to decrease this interference, or it is supposed to be like this and i have to decrease it by after processing?

THANKS.

  • 0 in reply to Fanyi Liu
    TI__Guru 63086 points

    Hi Fanyi, 

    These jumpers on JP25 provide several options for routing the BIAS and REF signals, which can also be tied together, so I understand your confusion here. I cannot pretend to be an expert in EEG, but I will explain some of the options featured on the ADS1299 EVM and hopefully you can let me know which makes the most sense for your application.

    The BIAS signal on the ADS1299 can be derived from selected channel inputs as explained in the INPUT MULTIPLEXER (Rerouting the BIAS Drive Signal) section of the datasheet. The output of the BIAS_AMP can be used to drive the patient, and it can also be fed back into the MUX and measured. This BIAS drive signal drives the patient with an inverted common-mode signal that can help reduce noise and 50/60Hz interference.

    The REF signal, as I understand, is a common electrode on the body that each measurement is referenced to. Using single-ended inputs, as you described, would mean that each signal electrode is connected to INxP, while the reference is connected to all INxN, This can be done either directly on the appropriate pins of J6 (i.e. pins 34 and 30) or through the SRB1 pin (REF_ELEC routes to SRB1 directly or buffered, using JP6, JP7, and JP8). SRB1 routes the REF signal to all INxN pins internally. It may be useful to experiment with these options for best performance as the input impedance will be different.

    JP25 [5-6] offers the ability to connect the BIAS and REF signals together. However, I do not know how common or useful this is. If you compared EEG to ECG (where BIAS = RLD and REF = LL), I do not think I have seen anyone tie the two signals together, but perhaps you know a reason for doing so. :)

    Best Regards,

  • 0
    Prodigy 50 points

    Dear Fanyi:

    For SE inputs I've configured the jumpers set as you did, but adding JP1 2-3 that is missing on your board. As the EVAL board gives only an internal reference for the BIAS_AMP (BIASREF_INT=1), you should jump JP1 2-3 to join BIASOUT with BIASIN and drive it out (RLD),  through CHx[2:0]=110 or 111.

    I hope it will work

    Regards

    Anibal

  • 0 in reply to Anibal Laquidara
    TI__Guru 63086 points

    Thanks for your input, Anibal!

    Fanyi, one thing to keep in mind when driving the BIAS signal to the patient through INxP or INxN (CHx[2:0]=110 or 111) is that the selected channel cannot be used for measurements simultaneously. Choose an unused channel to drive the patient.

    Regards,