Datasheet

+
V
OUT
+
-
-
R
A
C
F
V
IN
= KI
+
-
IR RADIATION
INTENSITY, I
V
OUT
R
A
K(R
A
+ R
B
)
I =
IR SENSOR
R
B
OP AMP
OPEN LOOP
GAIN
NOISE GAIN WITH NO C
F
NOISE GAIN WITH C
F
f
Z
f
P
A
0
f
Z
=
1
2S
R
F
C
IN
f
P
=
A
0
2S
R
F
(C
IN
+C
F
)
GAIN
FREQUENCY
LM6211
www.ti.com SNOSAH2C –FEBRUARY 2006–REVISED MARCH 2013
Figure 50. Method for C
F
selection
SENSOR INTERFACES
The low input bias current and low input referred noise of the LM6211 make it ideal for sensor interfaces. These
circuits are required to sense voltages of the order of a few μV, and currents amounting to less than a nA, and
hence the op amp needs to have low voltage noise and low input bias current. Typical applications include infra-
red (IR) thermometry, thermocouple amplifiers and pH electrode buffers. Figure 51 is an example of a typical
circuit used for measuring IR radiation intensity, often used for estimating the temperature of an object from a
distance. The IR sensor generates a voltage proportional to I, which is the intensity of the IR radiation falling on
it. As shown in Figure 51, K is the constant of proportionality relating the voltage across the IR sensor (V
IN
) to the
radiation intensity, I. The resistances R
A
and R
B
are selected to provide a high gain to amplify this voltage, while
C
F
is added to filter out the high frequency noise.
Figure 51. IR Radiation Sensor
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