Datasheet

R
1
R
2
R
3
R
4
10 k:
V
IN
V
OUT
+
-
V
+
V
-
+
-
V
+
V
-
= 1 +
R
2
R
1
R
4
R
3
+
V
OUT
+
-
-
R
A
C
F
V
IN
= KI
+
-
IR RADIATION
INTENSITY, I
THERMOPILE
R
B
V
OUT
R
A
K(R
A +
R
B
)
I =
LMP7711
SNOSAP4F –SEPTEMBER 2005–REVISED MAY 2013 www.ti.com
Figure 61. Thermopile Sensor Interface
PRECISION RECTIFIER
Rectifiers are electrical circuits used for converting AC signals to DC signals. Figure 62 shows a full-wave
precision rectifier. Each operational amplifier used in this circuit has a diode on its output. This means for the
diodes to conduct, the output of the amplifier needs to be positive with respect to ground. If V
IN
is in its positive
half cycle then only the output of the bottom amplifier will be positive. As a result, the diode on the output of the
bottom amplifier will conduct and the signal will show at the output of the circuit. If V
IN
is in its negative half cycle
then the output of the top amplifier will be positive, resulting in the diode on the output of the top amplifier
conducting and, delivering the signal on the amplifier's output to the circuits output.
For R
2
/ R
1
≥ 2, the resistor values can be found by using the equation shown in Figure 62. If R
2
/ R
1
= 1, then R
3
should be left open, no resistor needed, and R
4
should simply be shorted.
Figure 62. Precision Rectifier
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