Datasheet

12
®
INA121
INA121
R
G
/2
R
G
= 5.6kΩ
V
O
LA
RL
RA
10kΩ
Ref
NOTE: Due to the INA121’s current-feedback
topology, V
G
is approximately 0.7V less than
the common-mode input voltage. This DC offset
in this guard potential is satisfactory for many
guarding applications.
Low bias current
allows use with high
electrode impedances.
G = 10
2.8kΩ
V
G
V
G
2.8kΩ
1/2
OPA2131
390kΩ
390kΩ
1/2
OPA2131
FIGURE 12. Multiplexed-Input Data Acquisition System.
FIGURE 13. Shield Driver Circuit.
INA121
V
IN
–
V
IN
+
OPA130
511Ω
22.1kΩ
22.1kΩ
Ref
V
O
For G = 100
R
G
= 511Ω // 2(22.1kΩ)
effective R
G
= 505Ω
100Ω
NOTE: Driving the shield minimizes CMR degradation
due to unequally distributed capacitance on the input
line. The shield is driven at approximately 1V below
the common-mode input voltage.
FIGURE 14. ECG Amplifier With Right-Leg Drive.
INA121
V
IN
+
–
V
IN
+
–
Channel 8
Channel 1
MPC800
MUX
ADS7816
+5V
V
REF
+In
–In
12 Bits Out
Serial
R
G
Ref