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Original question:

ADS1299 Evaluation Module Setup

ADS1299: ADS1299 Evaluation Module Setup

Javier Ortiz
Prodigy 40 points
Part Number: ADS1299

Hello,

My question is about Reference electrode and Bias electrode connections and ADS1299 EVM setup to measure single ended Channels with single 5 V AVVD.

Previously I want to remark some stements from TI documents.

From the SBAS499A document (ADS1299 datasheet)
Figure 21. Methods of Driving the ADS1299: Single-Ended or Differentialsigle.
It is said that"When the input is single-ended, the INN input is held at the common-mode voltage, preferably at midsupply"
in the block-scheme the VCM is connected to INxN pins (internally connected to inverted input of the low noise PGAx) .

In the SLAU443B document: EEG Front-End Performance Demonstration Kit User's guide
7.1 Reference Signal and Patient Bias Signal:
"The EVM has two signals (BIAS_ELEC, REF_ELEC) available at the connector JP25 that correspond to these two electrodes".
"The reference signal is used as the reference for the single-ended EEG measurements. The patient bias signal is used
for biasing the patient to set the common mode of the EEG signals (typically mid supply)".

Now the questions:

I want to use a earlobe (or any other electrode) as reference electrode and measure eight channels in single-ended mode

I connect this reference electrode REF_ELEC connector pin.

Should I connect jumpers 5-6 in JP25 to connect BIAS_ELEC (VCM=Internal MidSupply voltage) to REF_ELEC and
also jumpers 1-2 in JP8 to link REF_ELEC to SRB1 pin and internally to all INxN just as it is draw in single-ended scheme?

Or, Have I also the option to connect just jumpers 1-2 in JP8 without connecting jumpers 1-6 in JP25? Means: REF_ELEC link to SRB1.

What is the difference between both configurations?

Would not it be necessary to drive the VCM in INxN channels?

Case I use the Patient Bias Drive (BIASOUT linked to BIAS_ELEC and BIAS ELECTRODE), Is there any impact in the above reference electrode configuration?

Thank You

Javier

 

  • 0
    TI__Mastermind 47625 points
    Hello Javier,

    Thanks for your post!

    Connecting JP25 to pins 5-6 and JP8 to 1-2 will connect BIAS_ELEC to REF_ELEC and then to SRB1 which will connect to all of the negative inputs.

    This is fine if you would like to use BIAS_ELEC to measure your single ended signal against.

    As you pointed out with your second approach, only connecting JP8 1-2 would leave your REF_ELEC and therefor your negative inputs floating which would not be ideal. However, you could connect your earlobe reference electrode to pin 6 of JP25 and drive REF_ELEC and therefor your negative inputs with the reference voltage.