Texas Instruments ADS1299, Руководство пользователя

Страница: 35 / 68

BIASIN
To PGAP
VINN
VINP
From
LOFFP
TESTP
TEMPM
ADS1299 Mux
Mux[2:0] = 001
0.75 x VDD
Mux[2:0] =011
Mux[2:0] =100
0.25 x VDD
Mux[2:0] =101
TESTM
Mux[2:0] =101
Mux[2:0] =110
Mux[2:0] =111
Mux[2:0] = 001
To PGAN
Mux[2:0] =010 AND
BIAS_MEAS
From
LOFFM
Mux[2:0] =011
Mux[2:0] =100
TEMPP
INT_TEST
(VREFP+VREFN)
2
Mux[2:0] = 010
AND BIAS_MEAS
SRB1 SRB2
To Next Chans
INT_TEST
CHxSET[3] =1
MAIN AND SRB1
To Next Chans
MAIN AND SRB1
MAIN
BIASREF_INT=0
BIAS
REF
(AVDD+AVSS)
2
BIASREF_INT=1
AC
TEST
NOTE:
MAIN = Mux[2:0] =000 OR Mux[2:0] = 111OR Mux[2:0] = 110
www.ti.com
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
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).
35 SLAU443 – May 2012 EEG Front-End Performance Demonstration Kit
Submit Documentation Feedback
Copyright © 2012, Texas Instruments Incorporated