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
10k
100k 1M 10M
FREQUENCY (Hz)
60
70
80
90
100
110
120
GAIN (dB)
C
IN
= 50 pF
C
F
= 4.5 pF
+
-
+
-
797B
797A
C
IN
= 50 pF
47 k:
4.5 pF
1 k:
0.1 PF
10 k:
+
-
V
OUT
I
IN
V
OUT
I
IN
= 470,000
A
TI
=
LMV796, LMV797
SNOSAU9D MARCH 2006REVISED MARCH 2013
www.ti.com
Figure 57. 1.5 MHz Transimpedance Amplifier with A
TI
= 470000
Figure 58. 1.5 MHz Transimpedance Amplifier Frequency Response
SENSOR INTERFACES
The low input bias current and low input referred noise of the LMV796 and LMV797 make them 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 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 59 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 59, 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 59. IR Radiation Sensor
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