SLAU443 Datasheet, PDF (35/68 Pages) Texas Instruments – EEG Front-End Performance Demonstration Kit

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EEG Specific Features
The reference voltage for the on-chip right leg drive can be driven externally. The on-chip voltage is set to
mid-supply. If the application requires the common mode to be set to any other voltage, this configuration
can be accomplished by setting the appropriate bit in the Configuration 3 Register. The external BIASREF
voltage is set by resistor R1 and adjustable resistor R2.
The following procedure needs to be applied to activate the Bias drive circuitry:
Step 1. Set the inputs to Normal Electrode, refer Figure 38
To Next Chans
INT_TEST
Mux[2:0] =101
TESTP
To Next Chans
ADS1299 Mux
VINP
CHxSET[3] =1
TEMPP
0.75 x VDD
From
LOFFP
VINN
From
LOFFM
(AVDD+AVSS)
2
0.25 x VDD
TEMPM
Mux[2:0] =100
Mux[2:0] =011
MAIN
Mux[2:0] =110
Mux[2:0] =111
MAIN AND SRB1
Mux[2:0] = 010
AND BIAS_MEAS
Mux[2:0] = 001
Mux[2:0] = 001
To PGAP
(VREFP+VREFN)
2
To PGAN
BIASREF_INT=1
BIASREF_INT=0
Mux[2:0] =011
Mux[2:0] =100
Mux[2:0] =101
Mux[2:0] =010 AND
BIAS_MEAS
MAIN AND SRB1
INT_TEST
TESTM
TEST
NOTE:
MAIN = Mux[2:0] =000 OR Mux[2:0] = 111OR Mux[2:0] = 110
AC
Figure 38. Settings for Normal Electrode
Step 2. Turn on the bias drive buffer and set the internal bias drive reference; refer to Figure 39.
Figure 39. Configuring BIASREF and Bias Drive Buffer
Step 3. Select the electrodes to be chosen for the bias drive loop. In this case, the channel 1 and 2
input signals are used (as Figure 40 shows).
SLAU443 – May 2012
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EEG Front-End Performance Demonstration Kit
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