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