SLAU443 Datasheet, PDF (33/68 Pages) Texas Instruments – EEG Front-End Performance Demonstration Kit

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EEG Specific Features
Figure 36. Dedicated Reference and Bias Electrode
Reference : The reference electrode (REF_ELEC) input is used to drive the negative inputs of the
channel through SRB1 pin on ADS1299 device. The reference electrode is connected to the negative
inputs of all the channels. This leads to increased leakage current on the reference electrode since current
of all the channels gets added. The EVM provides an option to buffer the reference electrode to reduce
the leakage. The disadvantage of the buffered approach is the additional noise of the buffer amplifier. The
table below shows the jumper settings for the two options.
Table 9. Dedicated Reference Drive Options through
REF_ELEC
JP7
JP8
Un Buffered
Don’t care
1-2
Buffered
1-2
2-3
Bias : There is an option to provide the bias to a fixed electrode either through BIAS_ELEC or through
BIAS_DRV. BIAS_ELEC option needs an external amplifier U11 to buffer the mid supply. For the
BIAS_DRV option the buffer is built inside the ADS1299 chip. The BIAS_DRV option also helps in
improving common mode rejection by implementing a feedback loop. The details on selecting the inputs
for bias drive are discussed in Section 5.5.3 and Section 7.1.3.
SLAU443 – May 2012
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EEG Front-End Performance Demonstration Kit
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