Settings For Normal Electrode; Configuring Biasref And Bias Drive Buffer - Texas Instruments ADS1299EEG-FE User Manual

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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
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CHxSET[3] = 1
VINP
VINN
(AVDD+AVSS)
TEST
AC
Step 2. Turn on the bias drive buffer and set the internal bias drive reference; refer to
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
SLAU443 – May 2012
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INT_TEST
Mux[2:0] =101
Mux[2:0] =100
TEMPP
Mux[2:0] =011
0.75 x VDD
From
LOFFP
MAIN
Mux[2:0] =110
Mux[2:0] =111
MAIN AND SRB1
From
LOFFM
BIASREF_INT=1
2
BIASREF_INT=0
Mux[2:0] =011
0.25 x VDD
Mux[2:0] = 100
TEMPM
Mux[2:0] =101
INT_TEST
NOTE:
MAIN = Mux[2:0] =000 OR Mux[2:0] = 111 OR
Figure 38. Settings for Normal Electrode
Figure 39. Configuring BIASREF and Bias Drive Buffer
Figure 40
Copyright © 2012, Texas Instruments Incorporated
Figure 38
TESTP
ADS1299 Mux
Mux[2:0] = 010
Mux[2:0] = 001
AND BIAS_MEAS
Mux[2:0] = 001
Mux[2:0] =010 AND
BIAS_MEAS
TESTM
Mux[2:0] = 110
shows).
EEG Front-End Performance Demonstration Kit
EEG Specific Features
To Next Chans
To PGAP
(VREFP+VREFN)
2
To PGAN
MAIN AND SRB1
Figure 39.
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